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Pololu - Pololu 3pi Robot User`s Guide

1. EE m Build O Message a Find in Files 4 Breakpoints and Tracepoints AVR Studio build window compiling the example project Connect your programmer to your computer and to the ISP port of your 3pi and turn on the 3pi s power by pressing the button labeled POWER If you are using the Pololu Orangutan Programmer the green status LED close to the USB connector should be on while the other two LEDs should be off indicating that the programmer is ready Warning Do not attempt to program your 3pi if its batteries are drained or uncharged make sure you charge any new rechargeable batteries fully before you first use them Losing power during programming could permanently disable your 3pi Note Your programmer must be installed correctly before you use it If you are using the Orangutan USB programmer please see its user s guide http www pololu com does 0J36 for installation instructions Pololu 3pi robot with an Orangutan USB programmer connected to its ISP port 6 Programming Your 3pi Page 21 of 56 Pololu 3pi Robot User s Guide Select Tools gt Program AVR gt Connect to connect to the programmer For the Orangutan Programmer the default options of STK500 or AVRISP and Auto should be fine so click Connect and the AVRISP programming window should appear You will use AVRISP to load test hex into the flash memory of your 3pi To do this click in the Flash se
2. 0xC1 M1 forward 1 0 Sets motor M1 turning forward with a speed of 0 off up to 127 full speed 0xC2 M1 backward 1 0 Sets motor M1 turning backward with a speed of 0 off up to 127 full reverse OxC5 M2 forward 1 0 Sets motor M2 turning forward with a speed of 0 off up to 127 full speed OxC6 M2 backward 1 0 Sets motor M2 turning backward with a speed of 0 off up to 127 full reverse Source code include lt pololu 3pi h gt A A HF A 3pi serial slave An example serial slave program for the Pololu 3pi Robot See the following pages for more information http www pololu com docs 0d21 http www pololu com docs 0J20 http www poolu com PID constants unsigned int pid enabled 0 unsigned char max_speed 255 unsigned char p_num 0 unsigned char p den 0 unsigned char d_num 0 unsigned char d den 0 unsigned int last_proportional 0 unsigned int sensors 5 This routine will be called repeatedly to keep the PID algorithm running void pid check if pid enabled return Do nothing if the denominator of any constant is zero if p_ den 0 d den 0 set_motors 0 0 return Read the line position with serial interrupts running in the background serial set mode SERIAL AUTOMATIC unsigned int position read line sensors IR _EMITTERS ON serial set_mode SERIAL CHECK The proportional term should be 0 when we
3. 40k pdf 5 How Your 3pi Works Page 17 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 6 Programming Your 3pi To do more with your 3pi than explore the demo program you will need to program it which requires an external AVR ISP programmer such as our Orangutan USB programmer http www pololu com catalog product 740 Your first step should be to set up your programmer by following its installation instructions If you are using the Orangutan USB programmer please see its user s guide http www pololu com docs 0J6 Next you will need software that can compile your programs and transfer them to your 3pi via your programmer We recommend you download two software packages for this 1 WinAVR http winavr sourceforge net a free open source suite of development tools for the AVR family of microcontrollers including the GNU GCC compiler for C C 2 AVR Studio http www atmel com avrstudio Atmel s free integrated development environment IDE that natively works with WinAVR s free GCC C C compiler AVR Studio includes AVR ISP software that will let you upload your programs to the 3pi Note You can also program your 3pi using the Arduino IDE and an external ICSP programmer such as our Orangutan USB programmer For instructions on this approach please see our guide Programming Orangutans and the 3pi Robot from the Arduino Environment http www pololu com docs 0J17 The rest of this guide
4. Pololu 3pi Robot User s Guide music buffer i read next byte if check data byte music buffer i return add the end of string character 0 music buffer i 0 play music buffer Clears the LCD void do clear clear Displays data to the screen void do print unsigned char string length read next byte if check data byte string length return unsigned char i for i 0 i lt string length i unsigned char character character read_next_byte if check_data_byte character return Before printing to the LCD we need to go to AUTOMATIC mode Otherwise we might miss characters during the lengthy LCD routines serial_set_mode SERIAL AUTOMATIC print_character character serial set_mode SERIAL CHECK Goes to the x y coordinates on the lcd specified by the two data bytes void do lcd goto _xy unsigned char x read_next_byte if check data byte x return unsigned char y read_next_byte if check _data_byte y return led_goto_xy x y Runs through an automatic calibration sequence void auto calibrate time_reset set_motors 60 60 while get_ms lt 250 calibrate line sensors IR_EMITTERS ON set_motors 60 60 while get_ms lt 750 calibrate line sensors IR_ EMITTERS ON set_motors 60 60 while get_ms lt 1000 calibrate line sensors IR EMITTERS ON set_motors 0 0
5. send_calibrated_sensor values 1 break case char 0xBO send _trimpot break case char 0xB1 send battery millivolts break case char 0xB3 do_play 2001 2009 Pololu Corporation 10 Expansion Information Page 49 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation break case char 0xB4 calibrate line sensors IR EMITTERS ON send calibrated sensor values 1 break case char 0xB5 line sensors reset calibration break case char 0xB6 send_ line position break case char 0xB7 do_clear break case char 0xB8 do_print break case char 0xB9 do_lcd_goto_xy break case char 0xBA auto_calibrate break case char 0xBB set pid break case char 0xBC stop pid break case char 0xCl ml _forward break case char 0xC2 ml _backward break case char 0xC5 m2_forward break case char 0xC6 m2_backward break default clear print Bad cmd lcd goto _xy 0 1 print_hex_byte command play o7116crc continue bad command 10 b Serial master program A serial master program used to control the serial slave program is included with the Pololu AVR Library see Section 6 a in libpololu avr examples 3pi serial master The program is designed to run on an LV 168 or 3pi as a demonstration of what is possible but you will probably want to adapt it for your own
6. serial send blocking c 1 Turns on PID according to the supplied PID constants O 2001 2009 Pololu Corporation 10 Expansion Information Page 48 of 56 Pololu 3pi Robot User s Guide void set _pid unsigned char constants 5 unsigned char i for i 0 i lt 5 i constants i read next byte if check data byte constants i return make the max speed 2x of the first one so that it can reach 255 max speed constants 0 127 255 constants 0 2 set the other parameters directly p_num constants 1 p_den constants 2 d_num constants 3 d_den constants 4 enable pid pid_enabled 1 Turns off PID void stop pid set_motors 0 0 pid_enabled 0 AAA AAA AAA AAA TTI TTT TATA ATT TATA ATT AAA AA AAA AAA AAA AAA int main pololu_3pi_init 2000 play mode PLAY CHECK clear print Slave start receiving data at 115 2 kbaud serial set _baud rate 115200 serial set_mode SERIAL CHECK serial receive ring buffer 100 while 1 wait for a command char command read next byte The list of commands is below add your own simply by choosing a command byte and introducing another case statement switch command case char 0x00 slient error probable master resetting break case char 0x81 send signature break case char 0x86 send_raw_sensor values break case char 0x87
7. FIRST MAIN LOOP BODY when we find the goal we use break to get out of this Now enter an infinite loop we can re run the maze as many times as we want to while 1 Beep to show that we finished the maze Wait for the user to press a button INES ES for i 0 i lt path_length i SECOND MAIN LOOP BODY Follow the last segment up to the finish follow _segment Now we should be at the finish Restart the loop The first main loop needs to drive down a segment of the course decide how to turn and record the turn in the path variable To pass the correct arguments to select_turn we need to carefully examine the intersection as we cross it Note that there is a special exception for finding the end of the maze The following code works pretty well at least at the slow speeds that we re using FIRST MAIN LOOP BODY follow _segment Drive straight a bit This helps us in case we entered the intersection at an angle 8 Example Project 2 Maze Solving Page 33 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Note that we are slowing down this prevents the robot from tipping forward too much set_motors 50 50 delay ms 50 These variables record whether the robot has seen a line to the left straight ahead and right whil examining the current intersection unsigned char found _left 0 unsigned char found straight 0
8. PB1 PB4 and PB5 PB2 PD2 PBO and PD4 PB1 PB4 PB5 and PD7 PCS through jumper ADC7 through jumper ADC6 through jumper PB3 PB4 PB5 PC6 PDO and PD1 inaccessable to user inaccessable to user jumper connects user potentiometer to pin ADC7 user connection pads for the 3 jumpered I Os motor 2 connection pads for optional expansion Arduino Pin digital pins 0 1 19 analog inputs 5 7 digital pins 5 and 6 digital pins 3 and 11 digital pins 14 18 digital pin 1 digital pin 7 digital inputs 9 12 and 13 digital pin 10 digital pins 2 8 and 4 digital pins 9 12 13 and 7 digital pin 19 analog input 7 analog input 6 digital pins 11 12 and 13 reset digital pins 0 and 1 9 Pin Assignment Tables Page 40 of 56 Pololu 3pi Robot User s Guide Pin Assignment Table Sorted by Pin ATmegal68 Pin PDO PD1 PD2 PD3 PD4 PDS PD6 PD7 PBO PB1 PB2 PB3 PB4 PBS PCO PCI PC2 PC3 PC4 PCS ADC6 ADC7 reset 3pi Function free digital I O free digital I O LCD control line RS M2 control line LCD control line E M1 control line M1 control line LCD data line DB7 LCD control line R W LCD data line DB4 buzzer M2 control line LCD data line DB5 LCD data line DB6 QTR RC reflectance sensor QTR RC reflectance sensor QTR RC reflectance sensor QTR RC reflectance sensor QTR RC reflectance sensor analog in
9. for example by calibrating a 90 turn based on the amount of time that it takes Third at 9 25 V all five of the IR LEDs can be powered in series so that they consume the lowest possible amount of power Note that you can switch the LEDs on and off to save even more power One other interesting thing about this power system is that instead of gradually running out of power like most robots the 3pi will operate at maximum performance until it suddenly shuts off This can take you by surprise so you might want your 3pi to monitor its battery voltage A simple circuit for monitoring battery voltage is built in to the 3pi Three resistors shown in VBAT the circuit at right comprise a voltage divider that outputs a voltage equal to two thirds of the it 38 battery voltage which will always be safely below the main microcontroller s maximum analog R30 Sa E input voltage of 5 V For example at a battery voltage of 4 8 V the battery voltage monitor port GER ADC6 will be at a level of 3 2 V Using 10 bit analog to digital conversion where 5 V is read as a value of 1023 3 2 V is read as a value of 655 To convert it back to the actual battery voltage multiply this number by 5000mVx3 2 and divide by 1023 This is handled conveniently by the read battery millivolts function provided in the Pololu AVR Library see Section 6 a for more information which averages ten samples and returns the battery voltage in m
10. orangutan h de lib OrangutanAnalog h J bin _ OrangutanBuzzer h J doc _ OrangutanDelay h Bi ib LJ OrangutanLCD h Bb ib _ OrangutanLEDs h gt a L OrangutanMotors h di mfile OrangutanPushbuttons h de pn L Pololu3pi h B sample L PololuQTRSensors h p share E pushbuttons h J source E gtr h utils The Pololu AVR Library header files installed correctly 6 b Compiling a Simple Program A very simple demo program for the 3pi is available in the folder examples atmega168 simple test 3pi using a few basic commands from the Pololu AVR Library Here is a copy of the source code include lt pololu 3pi h gt int main i print Hello play L16 ceg gt c while 1 6 Programming Your 3pi Page 19 of 56 Pololu 3pi Robot User s Guide red led 0 green_led 1 delay ms 100 5 red _led 1 green_led 0 delay ms 100 5 return 0 O 2001 2009 Pololu Corporation Navigate to the simple test 3pi folder double click on the file test aps and the project should open automatically in AVR Studio showing the C file AVR Studio C Users paul Desktop libpololu avr examples simple test 3pi test c o E 2 File Project Build Edit View Tools Debug Window Help ax DBM ds ts ABBEY AA MABAKE ED TE Trace Disabled ARALAR Se AVR GCC Sd x include lt pololu 3pi h gt n a default int main 2 3 Source Files E
11. speedl speed2 while 1 10 c Available I O on the 3pi s ATmegal68 The easiest way to expand your 3pi s capabilities is probably to turn your 3pi into a smart base that is controlled by the microcontroller of your choosing as described in Section 10 a This allows you to connect your additional electronics to your secondary microcontroller and only requires you to make connections to pins PDO and PD1 on the 3pi These two pins are completely unused digital I O lines that connect to the ATmegal68 s UART module when that module is enabled You can freely use PDO and PD1 for general purpose digital I O or you can use them for serial communication with another microcontroller a serially controlled device or a computer note that you will need to convert the signal to RS 232 levels or USB to communicate with a computer In addition to PDO and PD1 the 3pi robot has a limited number of I O lines that can be used as inputs for additional sensors or to control additional electronics such as LEDs or servos These I O lines can be accessed through the pads at the center of the 3pi between the two motors labeled PDO PD1 ADC6 ADC7 and PCS If you are using an expansion kit these lines are brought up to the expansion PCB Pins PC5 ADC6 and ADC7 are all connected to 3pi hardware via removable shorting blocks By removing the shorting block you can use these pins for your own electronics Pin PCS can be used as either a digital I O or a
12. 80 80 delay ms 400 break case S Don t do anything break The first line of the file like any C file that you will be writing for the 3pi contains an include command that gives you access to the functions in the Pololu AVR Library Within turn we then use the library functions delay_ms and set_motors to perform left turns right turns and U turns Straight turns are also handled by this function though they don t require us to take any action The motor speeds and the timings for the turns are parameters that needed to be adjusted for the 3pi as you work on making your maze solver faster these are some of the numbers that you might need to adjust To access this function from other C files we need a header file which is called turn n The header file just contains a single line void turn char dir This line declares the turn function without actually including a copy of its code To access the declaration each C file that needs to call turn adds the following line tinclude turn h Note the double quotes being used instead of angle brackets This signifies to the C compiler that the header file is in the project directory rather than being a system header file like 3pi h Always remember to put the code for your functions in the C file instead of the header file If you do it the other way you will be making a separate copies of the code in each file that includes the header The file fo
13. Getting Started with Your 3pi Robot Page 6 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation e 4 AAA batteries Any AAA cells will work but we recommend NiMH batteries which are rechargeable and can be purchased from Pololu http www pololu com catalog product 1002 or at a local store If you use rechargeable batteries you will also need a battery charger Battery chargers designed to connect to external series battery packs may be used with the 3pi s battery charger port AVR ISP programmer with 6 pin connector The 3pi features an ATmegal68 microcontroller which requires an external programmer such as the Pololu Orangutan USB programmer http www pololu com catalog product 740 or Atmel s AVRISP series The 3pi has a standard 6 pin programming connector so your programmer will need to have a 6 pin ISP cable http www pololu com catalog product 972 for connecting to the target device You will also need whatever cable your programmer requires to connect to a computer Our Orangutan USB programmer requires a USB cable http www pololu com catalog product 130 that is not included with the programmer alone but is included as part of the 3pi programmer combo deal http www pololu com catalog product 747 A desktop or laptop computer You will need a personal computer for developing your code and loading it onto the 3pi The 3pi can be programmed on Windows Mac and Linux operating systems but Pololu suppor
14. Information Page 51 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation set the motor speeds void slave set _motors int speedl int speed2 char message 4 0xCl speedl 0xC5 speed2 if speedl lt 0 0xC2 ml backward speedl message 0 message 1 if speed2 lt 0 OxC6 m2 backward speed2 message 2 message 3 serial send blocking message 4 do calibration void slave calibrate serial _send AxB4 1 int tmp_buffer 5 read 10 characters but we won t use them serial_receive_blocking char tmp_buffer 10 100 reset calibration void slave reset calibration serial send blocking xB5 1 calibrate waits for a 1 byte response to indicate completion void slave _ auto calibrate int tmp buffer 1 serial send blocking AxBA 1 serial_receive blocking char tmp buffer 1 10000 sets up the pid constants on the 3pi for line following void slave set pid char max speed char p_num char p den char d_ num char d den char string 6 xBB string 1 max_speed string 2 p_num string 3 p_den string 4 d_num string 5 d den serial_send blocking string 6 stops the pid line following void slave_stop_pid serial send blocking xBC 1 clear the slave LCD void slave clear serial send blocking AxB7 1 5 print to the slave LCD void slave print char string serial
15. Reads all five IR sensors using calibrated values and estimates the position of a black line under the robot The value which is sent back as a two byte integer is 0 when the line is under sensor PCO or farther to the left 1000 when the line is directly under sensor PC1 up to 4000 when it is under sensor PC4 or farther to the right See Section 12 of of the Pololu AVR Library Command Reference for the formula used to estimate position Clears the LCD screen on the 3pi Prints 1 8 characters to the LCD The first byte is the length of the following string of characters as with the play command above Moves the LCD cursor to x y coordinates given by the next two bytes Turns the robot left and right while calibrating For use when the robot it positioned over a line Returns the character c when complete Sets up PID parameters and begins line following The first data byte sets the maximum motor speed The next four bytes a b c 10 Expansion Information Page 43 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation and d represent the PID parameters Specifically the difference in the motor speeds will be set to L 2000 xa b Dxc d where L is the position of the line as described above and D is the derivative of L The integral term is not implemented in this program See Section 7 c for more information on PID line following OxBC stop PID 0 0 Stops PID line following setting motor speeds to 0
16. are e Increase the maximum possible speed e Add more intermediate cases with intermediate speed settings to make the motion less jerky e Give your robot a memory have its maximum speed increase after it has been on the line consistently for a few cycles You might also want to e Measure the speed of your loop using timing functions from Section 2 of the command reference http www pololu com docs 0J18 to time a few thousand cycles or by blinking the LEDs on and off every 1000 cycles e Display sensor readings on the LCD Since writing to the LCD takes a significant amount of time you should do this at most few times per second 7 Example Project 1 Line Following Page 24 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation The A A AA A FF F FF F F HF 3 Incorporate the buzzer into your program You might want your 3pi to play music while it is driving or make informational beeps that depend on what it is doing See Section 4 of the command reference http www pololu com docs 0J18 for more information on using the buzzer for music you ll want to use the PLAY CHECK option to avoid disrupting your sensor readings entire source code to this simple line following program is presented below for your reference 3pi linefollower demo code for the Pololu 3pi Robot This code will follow a black line on a white background using a very simple algorithm It demonstrates auto calibra
17. are on the line int proportional int position 2000 Compute the derivative change of the position int derivative proportional last proportional Remember the last position 10 Expansion Information Page 44 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation last proportional proportional Compute the difference between the two motor power settings ml m2 If this is a positive number the robot will turn to the right If it is a negative number the robot will turn to the left and the magnitude of the number determines the sharpness of the turn int power difference proportional p _num p _ den derivative p_num p den Compute the actual motor settings We never set either motor to a negative value if power difference gt max speed power difference max speed if power difference lt max speed power difference max speed if power difference lt 0 set_motors max_speedtpower difference max speed else set_motors max_speed max speed power difference A global ring buffer for data coming in This is used by the read _ next byte and previous byte functions below char buffer 100 A pointer to where we are reading from unsigned char read _ index 0 Waits for the next byte and returns it Runs play check to keep the music playing and serial check to keep receiving bytes Calls pid_check to keep follow
18. is a function of the current reading It is easiest to turn the trimpot using a 2mm flat head screwdriver Sensors Show the current readings of the IR sensors using a bar graph Bigger bars mean lower reflectance Placing a reflective object such as your finger under one of the sensors will cause the corresponding reading to drop visibly on the graph This demo also displays C to indicate that button C has an effect press C and the IR emitters will be turned off In indoor lighting conditions away from bright incandescent or halogen lights all of the sensors should return entirely black readings with IR off Removing the jumper marked PCS disables control of the emitters causing them to always be on Motors Hold down A or C to run the motor on the corresponding side or hold down both buttons to run both motors simultaneously The motors will gradually ramp up to speed in your own programs you can switch them on much more suddenly Tap A or C to switch the corresponding motor to reverse the button letter becomes lowercase if pressing it will drive the corresponding motor in reverse Music Plays an adaptation of J S Bach s Fugue in D Minor for microcontroller and piezo while scrolling a text display This demonstrates the ability of the 3pi to play music in the background Timer A simple stopwatch Press C to start or stop the stopwatch and A to reset The stopwatch continues to count while you are exploring the other demos
19. its time to recharge or replace your batteries e The 3pi robot contains lead so follow appropriate handling procedures such as not licking the robot and washing hands after handling The 3pi robot is intended for use indoors on relatively flat smooth surfaces Avoid running your 3pi on surfaces that might scrape or damage the underside of your robot s PCB as it drives around e Avoid placing the robot so that the underside of the PCB makes contact with conductive materials e g do not place the 3pi in a bin filled with metal parts This could inadvertently short out the batteries and damage your robot even with the 3pi turned off Shorting various pads or components together could also damage your 3pi e Since the PCB and its components are exposed take standard precautions to protect your 3pi robot from ESD electrostatic discharge which could damage the on board electronics When picking up the 3pi you should first touch a safe part of the robot such as the wheels motors batteries or the edges of the PCB If you first touch components on the PCB you risk discharging through them When handing the 3pi to another person first touch their hand with your hand to equalize any charge imbalance between you so that you don t discharge through the 3pi as the exchange is made e Ifyou remove the LCD take care to replace it in the right orientation such that it is over the rear battery back It is possible to put the LCD in backwards or
20. music 0xB4 calibrate OxB5 reset calibration OxB6 line position OxB7 clear LCD 0xB8 print 0xB9 LCD goto xy OxBA autocalibrate OxBB start PID Data Response bytes bytes 0 2 101 2 9 6 10 10 O 2001 2009 Pololu Corporation Description Sends the slave name and code version e g 3p11 0 This command also sets motor speeds to 0 and stops PID line following if active so it is useful as an initialization command Reads all five IR sensors and sends the raw values as a sequence of two byte ints in the range 0 2000 Reads all five IR sensors and sends calibrated values as a sequence of two byte ints in the range 0 1000 Sends the voltage output of the trimpot as a two byte int in the range 0 1023 Sends the battery voltage of the 3pi in mV as a two byte int Plays a tune specified by a string of musical commands The first data byte specifies the length of the following string max length 100 so that the slave program knows how many more data bytes to read See the playQ command in Section 4 of the Pololu AVR Library Command Reference for a description of the musical command format Performs one round of calibration on the sensors This should be called multiple times as the robot moves over a range from white to black Resets the calibration This should always be used when connecting to a slave in case the master reset without a slave reset for example in case of a power glitch
21. offset doing so could damage the LCD or the 3pi 3 Important Safety Warning and Handling Precautions Page 5 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 4 Getting Started with Your 3pi Robot Getting started with your 3pi can be as simple as taking it out of the box adding batteries and turning it on The 3pi ships with a demo program that will give you a brief tour of its features optional user LEDs on pins PD1 and PD7 o gt ry 2 battery charger 4 coodo 2y connector SS firini La piezo buzzer on pin PB2 30 1 Micro 4 i Metal batteries Gearmotors not included optional power LED push on push off 3 power button ISP programming connector pin 1 removable 8x2 user pushbuttons character LCD on pins PB1 PB4 and PB5 General features of the Pololu 3pi robot top view integrated QTR RC reflectance sensors on digital pins PCO PC4 green user LED red user LED on pin PD7 on pin PD1 ATmega168 user microcontroller potentiometer running at 20 MHz LCD contrast adjustment LELETET blue power LED blue power LED tied to 9 25 V VBoost tied to 5 V VBat light weight plastic ball caster Labeled bottom view of the Pololu 3pi robot The following subsections will give you all the information you need to get your 3pi up and running 4 a What You Will Need The following materials are necessary for getting started with your 3pi 4
22. resources We would be delighted to hear from you about any of your projects and about your experience with the 3pi robot You can contact us http www pololu com contact directly or post on our forum http forum pololu com Tell us what we did well what we could improve what you would like to see in the future or share your code with other 3pi users 2 Contacting Pololu Page 4 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 3 Important Safety Warning and Handling Precautions The 3pi robot is not intended for young children Younger users should use this product only under adult supervision By using this product you agree not to hold Pololu liable for any injury or damage related to the use or to the performance of this product This product is not designed for and should not be used in applications where the malfunction of the product could cause injury or damage Please take note of these additional precautions Do not attempt to program your 3pi if its batteries are drained or uncharged Losing power during programming could permanently disable your 3pi If you have purchased rechargeable batteries for use with the 3pi do not assume they come fully charged charge them before you first use them The 3pi has the ability to monitor its battery voltage the example line following and maze solving programs we provide show how to use this feature and you should include it in your programs so you can know when
23. s Guide O 2001 2009 Pololu Corporation caster labeled 100 A desktop computer power supply also uses switching regulators peek through the vent in the back of your computer and look for a donut shaped piece with a coil of thick copper wire wrapped around it that s the inductor The power management subsystem built into the 3pi is shown in this block diagram VBAT VIN VOUT 9 25 V switching regulator VBOOST 9 25 V R33 1k VIN VOUT 50V linear regulator l vec 50V The voltage of 4 x AAA cells can vary between 3 5 5 5 V and even to 6 V if alkalines are used This means it s not possible simply to regulate the voltage up or down to get 5 V Instead in the 3pi a switching regulator first boosts the battery voltage up to 9 25 V Vboost and a linear regulator regulates Vboost back down to 5 V VCC Vboost powers the motors and the IR LEDs in the line sensors while VCC is used for the microcontroller and all digital signals Using Vboost for the motors and sensors gives the 3pi three unique performance advantages over typical robots which use battery power directly e First a higher voltage means more power for the motors without requiring more current and a larger motor driver e Second since the voltage is regulated the motors will run the same speed as the batteries drop from 5 5 down to 3 5 V You can take advantage of this when programming your 3pi
24. send blocking char length strlen serial_send_blocking serial_send_blocking xB8 1 string amp length 1 send the string length string length go to coordinates x y on the slave LCD void slave _lcd_goto_xy char x char y 10 Expansion Information Page 52 of 56 Pololu 3pi Robot User s Guide int serial send blocking AxB9 1 serial send blocking 8x 1 serial send blocking s8y 1 main char buffer 20 load the bar graph load_custom characters configure serial clock for 115 2 kbaud serial set _baud rate 115200 wait for the device to show up while 1 clear print Master delay ms 100 serial send x81 1 if serial_receive_ blocking buffer 6 50 continue clear print Connect lcd_goto_xy 0 1 buffer 6 0 print buffer clear the slave s LCD and display Connect and OK on two lines Put OK in the center to test x y positioning slave_clear slave_print Connect slave _lcd_goto_xy 3 1 slave print OK play a tune char tune xB3 11l606gab gt c tune 1 sizeof tune 3 serial send blocking tune sizeof tune 1 wait wait_for button ALL BUTTONS reset calibration slave _reset_calibration time reset slave auto calibrate unsigned char speedl 0 speed2 0 read sensors in a loop while 1 serial _send x87 1 returns calibrated sensor
25. shorting block color you most prefer or you can use a mixture of colors 4 Getting Started with Your 3pi Robot Page 8 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 5 How Your 3pi Works 5 a Batteries Introduction to Batteries The power system on the 3pi begins with the batteries so it is important to understand how your batteries work A battery contains a carefully controlled chemical reaction that pulls electrons in from the positive terminal and pushes them out of the negative terminal The most common type is the alkaline battery which is based on a reaction between zinc and manganese through a potassium hydroxide solution Once alkaline batteries are completely discharged they cannot be reused For the 3pi we recommend rechargeable nickel metal hydride NiMH batteries which can be recharged over and over NiMH batteries Two rechargeable AAA Ni MH batteries are based on a different chemical reaction from alkaline batteries but you don t need to know anything about the chemical details to use a battery everything you need to know about it is measured with a few simple numbers The first is the strength with which the electrons are pushed which we measure in volts V the units of electric potential An NiMH battery has a voltage of about 1 2 V To understand how much power you can get out of a battery you also need to know how many electrons the battery can push per second this is the
26. stop producing power This happens gradually the voltage and current produced by a battery will steadily drop until the energy runs out as shown in the graph below voltage V 2 n o a o o 0 2 4 6 8 time h Battery voltage vs time A rough measure of the amount of energy stored in a battery is given by its milliamp hour mAH rating which specifies how long the battery will last at a given discharge rate The mAH rating is the discharge rate multiplied by how long the battery lasts if you draw current at a rate of 200 mA 0 2 A and the battery lasts for 3 hours you would call it a 600 mAH battery If you discharge the same battery at 600 mA you would get about an hour of operation however battery capacity tends to decline with faster discharge rates so you might only get 50 minutes Note If you have purchased rechargeable batteries for the 3pi you should fully charge them before you first use them You should never attempt to program your 3pi if its batteries are drained or uncharged Losing power during programming could permanently disable your 3pi 5 b Power management Battery voltage drops as the batteries are used up but many electrical components require a specific voltage A special kind of component called a voltage regulator helps out by converting the battery voltage to a constant specified voltage For a long time 5 V has been the most common regulated voltage used in digital electronics this is also ca
27. that let s take a look at the second main loop which 1s very simple All we do is drive to the next intersection and turn according to our records After doing the last recorded turn the robot will be one segment away from the finish which explains the final follow_segment call in the outline of maze_solve above SECOND MAIN LOOP BODY follow_segment Drive straight while slowing down as before set_motors 50 50 delay _ms 50 set_motors 40 40 delay ms 200 8 Example Project 2 Maze Solving Page 34 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Make a turn according to the instruction stored in path i turn path i 8 e Simplifying the Solution After every turn the length of the recorded path increases by 1 If your maze for example has a long zigzag passageway with no side exits you ll see a sequence like RLRLRLRL appear on the 3pi s LCD There s no shortcut that would get you through this section of the path faster than just following the left hand on the wall strategy However whenever we encounter a dead end we can simplify the path to something shorter Consider the sequence LBL where B stands for back and is the action taken when a dead end is encountered This is what happens if there is a left turn that branches off of a straight path and leads immediately to a dead end After turning 90 left 180 and 90 left again the ne
28. 00 means that the line is directly under sensor 2 and so on 2 The value returned by read_line is divided into three possible cases gt 0 1000 the robot is far to the right of the line In this case to turn sharply left we set the right motor speed to 100 and the left motor speed to 0 Note that the maximum speed of the motors is 255 so we are driving the right motor at only about 40 power here gt 1000 3000 the robot is approximately centered on the line In this case we set both motors to speed 100 to drive straight ahead gt 3000 4000 the robot is far to the left of the line In this case we turn sharply to the right by setting the right motor speed to 0 and the left motor speed to 100 3 Depending on which motors are activated the corresponding LEDs are turned on for a more interesting display This can also help with debugging To open the program in AVR studio you may go to examples 3pi linefollower and simply double click on test aps Compile the program load it onto your 3pi and try it out You should find that your robot is able to follow the curves of your line course without ever completely losing the line However its motors are moving at a speed of at most 100 out of the maximum possible of 255 and the algorithm causes a lot of unnecessary shaking on the curves At this point you might want to work on trying to adjust and improve this algorithm before moving on to the next section Some ideas for improvement
29. 000 600000 b00000 b00000 b00000 600000 b00000 b11111 b11111 b11111 b11111 b11111 b11111 b11111 COO COO OC OOo OC Oo oO y This function loads custom characters into the LCD Up to 8 characters can be loaded we use them for 6 levels of a bar graph plus a back arrow and a musical note character void load custom _ characters lcd_load_custom_character levels 0 0 lcd load custom character levels 1 1 Y no offset e g one bar lcd load custom character levels 2 2 two bars g E etc lcd load custom character levels 4 3 skip level 3 lcd load custom character levels 5 4 lcd load custom character levels 6 5 clear the LCD must be cleared for the characters to take effect 10 levels of bar graph characters const char bar graph _characters 10 0 0 1 2 3 3 4 5 255 void display levels unsigned int sensors clear int 1 for 1 0 1i lt 5 1 Initialize the array of characters that we will use for the graph Using the space an extra copy of the one bar character and character 255 a full black box we get 10 characters in the array The variable c will have values from 0 to 9 since values are in the range of 0 to 1000 and 1000 101 is 9 with integer math char c bar _ graph characters sensors i 101 Display the bar graph characters print character c 10 Expansion
30. 00000 b00000 b11111 b11111 b11111 b11111 b11111 b11111 b11111 OO O O O OOOO O OG This function loads custom characters into the LCD Up to 8 characters can be loaded we use them for 7 levels of a bar graph void load_custom_characters lcd_load_custom_character levels 0 0 lcd load custom character levels 1 1 lcd load custom character levels 2 2 no offset e g one bar Sd sE y lcd_load custom character levels 3 3 e two bars etc lcd_load_custom_character levels 4 4 lcd load custom character levels 5 5 lcd load custom character levels 6 6 7 Example Project 1 Line Following Page 25 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation clear the LCD must be cleared for the characters to take effect This function displays the sensor readings using a bar graph void display readings const unsigned int calibrated_values unsigned char i for i 0 i lt 5 i Initialize the array of characters that we will use for the graph Using the space an extra copy of the one bar character and character 255 a full black box we get 10 characters in the array const char display characters 10 0 0 1 2 3 4 5 6 255 The variable c will have values from 0 to 9 since calibrated values are in the range of 0 to 1000 and 1000 101 is 9 with integer math char c display characters calibrat
31. 4445 655546 Ohh ESC SPOS BLESS 30 8 b Working with Multiple C Files in AVR Studio 2 ee 30 Sc Lett Hand on the Wall ost a ORL RRR ee ee GLO ee ae 32 8 d The Main Loop ia a ee ak AG Se ge ee i een fs 33 8 e Simplifying the Solution aa 35 8 f Improving the Maze Solving Code 1 2 ee 38 92 Pin Assignment ables a ne ee lee ieee OL A EA ELE Sie Ae RE OE OEE a 39 10 Expansion Informatica Gok ae hg ee es de Be a Sh ee 42 10 a Serial slave program 42 10 b Serial master program na s a a A E aA E a T a A d a A A A E A e a 50 10 c Available I O on the 3pi s ATmegal68 54 TI Related RESOUICES riain td e rt ds rad a ly Skt oh tee re land ios 56 Page 2 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 1 Introduction The Pololu 3pi robot is a small high performance autonomous robot designed to excel in line following and line maze solving competitions Powered by four AAA batteries not included and a unique power system that runs the motors at a regulated 9 25 V 3pi is capable of speeds up to 100 cm second while making precise turns and spins that don t vary with the battery voltage This results in highly consistent and repeatable performance of well tuned code even as the batteries run low The robot comes fully assembled with two micro metal gearmotors five reflectance sensors an 8x2 character LCD a buzzer three user pushbuttons and more all connected to a user programmable A
32. 6 jumpered to user trimmer potentiometer ADC input channel 7 ADC7 internally pulled high active low digital I O disabled by default 9 Pin Assignment Tables Page 41 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 10 Expansion Information 10 a Serial slave program The Pololu AVR library see Section 6 a comes with an example serial slave program for the 3pi in 1ibpololu avr examples 3pi serial slave and a corresponding serial master program in libpololu avr examples 3pi serial master This example shows how to use a ring buffer in SERIAL CHECK mode to continuously receive and interpret a simple set of commands The commands control various features of the 3pi making it possible to use the 3pi as a smart base controlled by another processor It is easy to add more commands yourself or adapt the library to work on a different board Note that we offer several expansion kits on which you can mount such a secondary microcontroller and additional electronics black with cutouts http www pololu com catalog product 979 that let you view the LCD underneath black without cutouts http www pololu com catalog product 978 that replaces the LCD and maximizes prototyping space red with cutouts http www pololu com catalog product 977 and red without cutouts http www pololu com catalog product 976 Complete documentation of the serial functions used here can be found in Section 9 of the Pololu AVR L
33. Hz LCD contrast adjustment blue power LED tied to 9 25 V VBoost blue power LED tied to 5 V VBat light weight plastic ball caster Labeled bottom view of the Pololu 3pi robot 9 Pin Assignment Tables Page 39 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation sensor locations circled in blue jumper connects 2 3rds of battery voltage to pin ADC6 prototyping space with power rails motor 1 alternate power button connection user connection pads for the two unused digital I Os serial pins PDO amp PD1 on pins pci PC2 p jumper connects IR sensor LEDs to pin PC5 C3 Specific features of the Pololu 3pi robot top view Pin Assignment Table Sorted by Function Function free digital I Os x3 remove PC5 jumper to free digital pin 19 free analog inputs if you remove jumpers x3 motor 1 left motor control A and B motor 2 right motor control A and B QTR RC reflectance sensors left to right x5 red left user LED green right user LED user pushbuttons left to right x3 buzzer LCD control RS R W E LCD data 4 bit DB4 DB7 reflectance sensor IR LED control drive low to turn IR LEDs off user trimmer potentiometer 2 3rds of battery voltage ICSP programming lines x3 reset pushbutton UART RX and TX I2C TWI SPI ATmegal68 Pin PDO PD1 PCS PCS ADC6 ADC7 PDS and PD6 PD3 and PB3 PCO PC4 PDI PD7
34. Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Pololu 3pi Robot User s Guide Page 1 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation TelitroductiOn cda E A ATA ee Oe Ae AO EE ae ts 3 2 Contacting Pololu ise da td eed fas Se AE end Sint ie pe lg ed fg ok eed ck 4 3 Important Safety Warning and Handling Precautions e 5 4 Getting Started with Your 3piRobot a 6 Aa What You WilNEcd A 202 amp ee u e a i E y Ge She ie is e A A a A 6 4 D Powering Up YoUr Ipi id ela ie lr amp Ee a 7 4 c Using the Preloaded Demo Program aoaaa ee 7 A dalnel d d Accessories ai so ar A GO A A as a ee ae 8 SHOW Your Spl Woks 2 cs g E oR eR A EE ee ae E Bee EG RA TAS 9 Sa Batteries T e aa O A A a e Geter a ido a 9 Sb Power management socis ae e See A A ee eh A ESS 10 5 c Motors and Gearboxes Kabla ae a ee 12 5 d Digital inputs and sensors ar es a PE A SR Se ee EEE a G 14 5 e 3pi Simplified Schematic Diagram 2 1 a 16 6 Programming Your AA 18 6 a Downloading and Installing the C C Library o o 18 6 b Compiling a Simple Programa 19 7 Example Project 1 Line Following 2 a i ee 23 7 a About Line Following ee a ee ee 23 7 b A Simple Line Following Algorithm for 3pi 2 0 ee ee 23 7 c Advanced Line Following with 3pi PID Control 2 2 ee 28 8 Example Project 2 Maze Solving 2 ee 30 S a Solving a Eime Maze an oe e ees 6
35. The source code for the demo program is included with the Pololu AVR C C Library described in Section 6 After downloading and unpacking the library zip file the demo program can be found in the folder examples 3pi demo program 4 d Included Accessories The 3pi robot ships with two through hole red LEDs and two through hole green LEDs There are connection points for three optional LEDs on your 3pi one next to the power button to indicate when the 3pi is on and two user controllable LED ports near the front edge of the robot Using these LEDs is completely optional as the 3pi will function just fine without them You can customize your 3pi by choosing your desired combination of red and green LEDs or you can even use your own LEDs http www pololu com catalog category 20 if you want more color brightness options Q gt a e Z Note that you should only add LEDs if you are comfortable soldering and you should take care to avoid desoldering any of the components near the through hole LED pads LEDs are polarized so be sure to solder them such that the longer lead connects to the pad marked with the Before you solder them in you can press fit them in place and check to make sure they light as expected Once soldered in place carefully trim off the excess portion of the LED leads Your 3pi also ships with three shorting blocks of each color blue red yellow black This means you can customize your 3pi by selecting the
36. V unsigned int read battery millivolts return readAverage 6 10 5000L 3 2 1023 5 How Your 3pi Works Page 11 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 5 c Motors and Gearboxes A motor is a machine that converts electrical energy to motion There are many different kinds of motors but the most important for low cost HE robotics is the brushed DC motor which is the type used on the 3pi A brushed DC motor typically has permanent magnets on the outside and several electromagnetic coils mounted on the motor shaft armature The brushes are sliding pieces of metal that switch the power from one coil to the next as the shaft turns so that magnetic attraction between the coil and the magnets continuously pulls the motor in the same direction A typical small brushed DC motor with no gearbox The primary values that describe a running motor are its speed measured in rpm and its torque measured in kg cm or oz in pronounced ounce inches The units for torque show the dependence on both force and distance for example a motor that produces 6 ozin of torque can product a force of 6 oz with a 1 inch lever arm 3 oz with a 2 inch lever and so on Multiplying the torque and speed measured at the same time give us the power delivered by a motor We see therefore that a motor with twice the speed and half the torque as another has the same power output Every motor has a maxi
37. VR microcontroller The 3pi measures approximately 3 7 inches 9 5 cm in diameter and weighs 2 9 oz 83 g without batteries The 3pi is based on an Atmel ATmegal68 microcontroller running at 20 MHz with 16KB of flash program memory and 1KB data memory The use of the ATmegal68 microcontroller makes the 3pi compatible with the popular Arduino development platform Free C and C development tools are also available and an extensive set of libraries make it a breeze to interface with all of the integrated hardware Sample programs are available to show how to use the various 3pi components as well as how to perform more complex behaviors such as line following and maze solving Please note that an external AVR ISP programmer such as our Orangutan USB Programmer http www pololu com catalog product 740 is required to program the 3pi robot You can download a pdf version of this user s guide here http www pololu com file download 3pi pdf file_id 0J169 2017k pdf For a Spanish version of this document please see Pololu 3pi Robot Guia Usuario http www pololu com file download Pololu3piRobotGuiaUsuario pdf file_id 0J137 2483k pdf provided by customer Jaume B 1 Introduction Page 3 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 2 Contacting Pololu You can check the 3pi product page http www pololu com catalog product 975 for additional information including pictures videos example code and other
38. al value records the history of your robot s motion it is a sum of all of the values of the proportional term that were recorded since the robot started running The derivative is the rate of change of the proportional value We compute it in this example as the difference of the last two proportional values Here is the section of code that computes the PID input values Get the position of the line Note that we must provide the sensors argument to read_line here even though we are not interested in the individual sensor readings unsigned int position read_line sensors IR_ EMITTERS ON The proportional term should be 0 when we are on the line int proportional int position 2000 Compute the derivative change and integral sum of the position int derivative proportional last_proportional integral proportional 7 Example Project 1 Line Following Page 28 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Remember the last position last proportional proportional Note that we cast the variable position to an int type in the formula for proportional An unsigned int can only store positive values so the expression position 2000 without casting would lead to a negative overflow In this particular case it actually wouldn t affect the results but it is always a good idea to use casting to avoid unexpected behavior Each of these input values prov
39. controller To use the program make the following connections between your master and slave GND GND PDO PD1 PD1 PDO Turn on both master and slave The master will display a Connect message followed by the signature of the slave source code e g 3pil 0 The master will then instruct the slave to display Connect and play a short tune Pressing the B botton on the master causes the slave to go through an auto calibration routine after which you can drive the slave 10 Expansion Information Page 50 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation around using the A and C buttons on the master while viewing sensor data on the master s LCD Holding down the B button causes the slave to do PID line following Source code include lt pololu orangutan h gt include lt string h gt 3pi serial master An example serial master program for the Pololu 3pi Robot This can run on any board supported by the library it is intended as an example of how to use the master slave routines http www pololu com docs 0JdJ21 http www pololu com docs 0J20 http www poolu com AAA AA A HF CA Data for generating the characters used in load custom characters and display readings By reading levels starting at various offsets we can generate all of the 7 extra characters needed for a bargraph This is also stored in program space const char levels PROGMEM 600
40. ction and select file test hex that was compiled earlier Note that you have to first navigate to your project directory Now click Program in the Flash section and the test code should be loaded onto your 3pi If your 3pi was successfully programmed you should hear a short tune see the message Hello on the LCD and the LEDs on the board should blink If you hear the tune and see the lights flashing but nothing appears on the LCD make sure that the LCD is correctly plugged in to the 3pi and try adjusting the contrast using the small potentiometer on the Main Program Fuses LockBits Advanced HW Settings HW Info Auto Device IV Erase device before flash programming IV Verify device after programming Flash Fuses and lockbits settings Program Save must be specified before saving to ELF Programming the 3pi from AVR Studio underside of the 3pi closest to the ball caster O 2001 2009 Pololu Corporation 6 Programming Your 3pi Page 22 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 7 Example Project 1 Line Following 7 a About Line Following Now that you have learned how to compile a simple program for the 3pi it s time to teach your robot do something more complicated In this example project we 11 show you how to make your 3pi follow a black line on a white background by coordinating its sensors and motors Line following is a great introduction t
41. ction 6 b to try out some example programs on your 3pi 6 Programming Your 3pi Page 18 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Note To learn more about the functions in the Pololu AVR Library and how to use them please see the Pololu AVR Library Command Reference http www pololu com docs 0J18 Manual installation optional if the above instructions do not work Determine the location of your avr gcc files In Windows they will usually be in a folder such as C WinAVR 20080610 avr In Linux the avr gcc files are probably located in usr avr If you currently have an older version of the Pololu AVR Library your first step should be to delete all of the old include files and the 1ibpololu a file that you installed previously Next copy libpololu a into the 1ib subdirectory of your avr directory e g C WinAVR 20080610 avr 1lib Note that there is also a 1ib subdirectory directly below the main WinAVR directory it will not work to put 1ibpololu a here Finally copy the entire pololu subfolder into the include subfolder The Pololu include files should now be located in avr include pololu COn pololu y 4s Search p File Edit View Tools Help wy Organize y Folders v Name Date modified Type a WinAVR 20080430 a L 3pi h 7 B avr analog h p bi _ buzzer h z delay h s dl include E Icd h de avr _ leds h e compat _ motors h de pololu orangutan a util
42. dead end as we identify it 8 Example Project 2 Maze Solving Page 36 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation L SB B L L B L When we encounter the first intersection after our first back action we know we have reached a dead end that can be removed from our list of actions In this case the most recent actions in our list is the sequence SBL and the diagram shows that this sequence can be simplified into a single right turn R Prune out the rest of this dead end branch as we back track cansas B S L R B L4 B L bee s t Bt e We next end up with the sequence RBL which reduces to a single back B and this combines with the next action to produce the sequence LBL which reduces to a single straight S Prune out the final dead end branch to leave us with the shortest path from start to finish 8 Example Project 2 Maze Solving Page 37 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation cansan S B L R The last dead end gives us the sequence SBL which reduces to a sigle right turn R Our action list is now just R and represents the shortest path from start to finish As we drove the maze our action list would have looked like the following E A A E E LS LSB LSBL gt LR pruning occurs here LRB LRBL gt LB pruning occurs here LBL gt S pruning occurs here SB SBL gt R pruning occur
43. defined somewhere int main unsigned int sensors 5 an array to hold sensor values set up the 3pi initialize This is the main loop it will run forever while 1 Get the position of the line Note that we must provide the sensors argument to read_line here even though we are not interested in the individual sensor readings unsigned int position read line sensors IR EMITTERS ON if position lt 1000 We are far to the right of the line turn left Set the right motor to 100 and the left motor to zero to do a sharp turn to the left Note that the maximum value of either motor speed is 255 so we are driving it at just about 40 of the max set_motors 0 100 Just for fun indicate the direction we are turning on the LEDs left_led 1 right_led 0 else if position lt 3000 7 Example Project 1 Line Following Page 27 of 56 Pololu 3pi Robot User s Guide We are somewhat close to being centered on the line drive straight set_motors 100 100 left led 1 right_led 1 else We are far to the left of the line turn right set_motors 100 0 left led 0 right_led 1 This part of the code is never reached A robot should never reach the end of its program or unpredictable behavior will result as random code starts getting executed If you really want to stop all actions at some point set your mot
44. ed values i 101 Display the bar graph character print_character c Initializes the 3pi displays a welcome message calibrates and plays the initial music void initialize unsigned int counter used as a simple timer unsigned int sensors 5 an array to hold sensor values This must be called at the beginning of 3pi code to set up the sensors We use a value of 2000 for the timeout which corresponds to 2000 0 4 us 0 8 ms on our 20 MHz processor pololu_3pi_init 2000 load_custom_characters load the custom characters Play welcome music and display a message print_from program _ space welcome _linel lcd goto _xy 0 1 print_from program space welcome _line2 play from program space welcome delay ms 1000 clear print_from program space demo_name_linel lcd goto _xy 0 1 print_from program space demo_name_line2 delay ms 1000 Display battery voltage and wait for button press while button_is pressed BUTTON_B int bat read_battery millivolts clear print _long bat print mV lcd_goto_xy 0 1 print Press B delay ms 100 Always wait for the button to be released so that 3pi doesn t start moving until your hand is away from it wait _for button release BUTTON B delay ms 1000 Auto calibration turn right and left while calibrating the sensors for counter 0 counter lt 80 counter if cou
45. electric current measured in amps A A current of 1 A corresponds to about 6x10 8 electrons flowing out one side and in to the other each second which is such a huge number that it s easier to talk about it just in terms of amps 1 A is also a typical current that a medium sized motor might use and it s a current that will put a significant strain on small AAA batteries For any battery if you attempt to draw more and more current the voltage produced by the battery will drop eventually dropping all the way to zero at the short circuit current the current that flows if you connect one side directly to the other with a thick wire Don t try this The wire might overheat and melt and the battery could explode The following graph shows a good model of how the voltage on a typical battery drops as the current goes up a o voltage V o on 0 0 0 1 2 3 current A Battery voltage vs current The power put out by a battery is measured by multiplying the volts by the amps giving a measurement in watts W For example at the point marked in the graph we have a voltage of 0 9 V and a current of 0 6 A this means that the power output is 0 54 W If you want more power you need to add more batteries and there are two ways to do it parallel and series configurations When batteries are connected in parallel with all of their positive terminals tied together and all of their negative terminals tied together the
46. following code implements a left hand on the wall strategy where we always turn as far to the left as possible 8 Example Project 2 Maze Solving Page 32 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation if found left return L else if found straight return S else if found right return R else return B The values returned by select turn correspond to the values used by turn so these functions will work nicely together in our main loop 8 d The Main Loop s The strategy of our program is expressed in the file maze solve c Most importantly we want to keep track of the path that we have followed so we define an array storing up to 100 these will be the same characters used in the turn function We also need to keep track of the current path length so that we know where to put the characters in the array char path 100 unsigned char path_length 0 the length of the path Our main loop is found in the function maze_solve which is called after calibration from main c This function actually includes two main loops a first one that handles solving the maze and a second that replays the solution for the fastest possible time In fact the second loop is actually a loop within a loop since we want to be able to replay the solution many times Here s an outline of the code This function is called once from main c void maze solve while 1
47. gram that demonstrates most of its features and allows you to test that it is working correctly When you first turn on your 3pi you will hear a beep and see the words Pololu 3pi Robot then Demo Program appear indicating that you are running the demo program If you hear a beep but do not see any text on the LCD you may need to adjust the contrast potentiometer on the underside of the board When the program has started successfully press the B button to proceed to the main menu Press C or A to scroll forward or backward through the menu and press B to make a selection or to exit one of the demos There are seven demos accessible from the menu 1 Battery This demo displays the battery voltage in millivolts which should be above 5000 5 0 Volts for a fully charged set of batteries Removing the jumper marked ADC6 will separate the battery voltage measurement circuit from the analog input causing the number displayed to drop to some low value 4 Getting Started with Your 3pi Robot Page 7 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation LEDs Blinks the red and green user LEDs on the underside of the board If you have soldered in the optional user LEDs they will also blink Trimpot Displays the position of the user trimmer potentiometer which is located on the underside of the board as a number between 0 and 1023 While displaying the value this demo also blinks the LEDs and plays a note whose frequency
48. his is mostly just to make the course easy to reproduce the maze solving strategy described in this tutorial does not require these features For information on building your own course see our tutorial on Building Line Following and Line Maze Courses http www pololu com docs 0J22 8 b Working with Multiple C Files in AVR Studio The C source code for an example line maze solver is available in the folder examples atmega168 3pi mazesolver Note An Arduino compatible version of this sample program can be downloaded as part of the Pololu Arduino Libraries http www pololu com docs 0J17 see Section 5 g The Arduino sample sketch is all contained within a single file This program is much more complicated than the examples you have seen so far so we have split it up into multiple files Using multiple files makes it easier for you to keep track of your code For example the file turn c contains only a single function used to make turns at the intersections include lt pololu 3pi h gt Turns according to the parameter dir which should be L R S straight or B back void turn char dir switch dir case L Turn left set motors 80 80 delay ms 200 break case R Turn right set_motors 80 80 delay ms 200 break case B 8 Example Project 2 Maze Solving Page 30 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Turn around set_motors
49. ibrary Command Reference http www pololu com docs 0J18 This slave program receives serial data on port PDO RX of the 3pi and transmits responses when necessary on port PD1 TX using a 115 2 kbaud TTL level serial protocol In this example there are no parity bits 8 data bits and one stop bit N81 The commands implemented here each consist of a single command byte followed by zero or more data bytes To make it easy to differentiate the command bytes from the data bytes the command bytes are all in the range 0x80 Oxff while the data bytes are in the range 0x00 0x7f That is the command bytes have their most significant bits set while the data bytes have that bit unset Some commands result in the 3pi sending data back out to the controlling device For commands where integers are sent back the least significant byte is sent first little endian If bad commands or data bytes are detected the slave program beeps and displays an error message on the LCD This means that if you are using the expansion kit without cutouts http www pololu com catalog product 978 you should probably remove the LCD related commands before loading the program onto your 3pi The following commands are recognized by the slave program 10 Expansion Information Page 42 of 56 Pololu 3pi Robot User s Guide command Command byte 0x81 signature 0x86 raw sensors 0x87 calibrated sensors OxB0 trimpot OxB1 battery millivolts 0xB3 play
50. ides a different kind of information The next step 1s a simple formula that combines all of the values into one variable which is then used to determine the motor speeds Compute the difference between the two motor power settings ml m2 If this is a positive number the robot will turn to the right If it is a negative number the robot will turn to the left and the magnitude of the number determines the sharpness of the turn int power difference proportional 20 integral 10000 derivative 3 2 Compute the actual motor settings We never set either motor to a negative value const int max 60 if power difference gt max power difference max if power difference lt max power difference max if power difference lt 0 set_motors max power difference max else set_motors max max power difference The values 1 20 1 10000 and 3 2 are adjustable parameters that determine how your 3pi will react to the line In general increasing these PID parameters will make power difference larger causing stronger reactions while decreasing them will make the reactions weaker It s up to you to think about the different values and experiment with your robot to determine what effect each parameter has This example gives the motors a maximum speed of 100 which is a safe initial value Once you have adjusted the parameters to work well at a speed of 100 try increasing the speed You ll probably
51. iles from the list When you build your project AVR Studio will automatically compile all C files in the project together to produce a single hex file 8 c Left Hand on the Wall The basic strategy for solving a non looped maze is called left hand on the wall Imagine walking through a real labyrinth a human sized maze built with stone walls while keeping your left hand on the wall at all times You ll turn left whenever possible and only turn right at an intersection if there is no other exit Sometimes when you reach a dead end you ll turn 180 degrees to the right and start walking back the way you came Eventually as long as there are no loops your hand will travel along each length of wall in the entire labyrinth exactly once and you ll find your way back to the entrance If there is a room somewhere in the labyrinth with a monster or some treasure you ll find that on the way since you ll travel down every hallway exactly twice We use this simple reliable strategy in our 3pi maze solving example This function decides which way to turn during the learning phase of maze solving It uses the variables found left found straight and found right which indicate whether there is an exit in each of the three directions applying the left hand on the wall strategy char select turn unsigned char found left unsigned char found straight unsigned char found right Make a decision about how to turn The
52. ing the line char read next byte while serial_get_received_bytes read_index serial check play check pid_check takes some time only run it if we don t have more bytes to process if serial get _received_bytes read index pid_check char ret buffer read_index read_index if read index gt 100 read_index 0 return ret Backs up by one byte in the ring buffer void previous byte read_index if read_index 255 read_index 99 Returns true if and only if the byte is a command byte gt 0x80 char is command char byte if byte lt 0 return 1 return 0 Returns true if and only if the byte is a data byte lt 0x80 char is data char byte if byte lt 0 return 0 return 1 If it s not a data byte beeps backs up one and returns true char check data_byte char byte 10 Expansion Information Page 45 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation ASAS o Peay ASAI RE E Re Soo O X vo vo Le if is data byte return 0 play o3c clear print Bad data lcd goto _xy 0 1 print hex byte byte previous byte return 1 AAA AAA AAA AAA AAA AA AAA AAA TTA CAAA AAAA ANAA AAA TTA TTT TT COMMAND FUNCTIONS Each function in this section corresponds to a single serial command The functions are expected to do their own argument handl
53. ing using read _ next byte and check data byte Sends the version of the slave code that is running This function also shuts down the motors and disables PID so it is useful as an initial command id send signature serial send blocking 3pi1 0 6 set_motors 0 0 pid enabled 0 Reads the line sensors and sends their values This function can do either calibrated or uncalibrated readings When doing calibrated readings it only performs a new reading if we are not in PID mode Otherwise it sends the most recent result immediately id send sensor values char calibrated if calibrated if pid enabled read line sensors calibrated sensors IR EMITTERS_ON else read_line _sensors sensors IR_EMITTERS_ON serial_send blocking char sensors 10 Sends the raw uncalibrated sensor values id send _raw_ sensor values send _ sensor values 0 Sends the calibated sensor values id send calibrated _ sensor values send sensor values 1 Computes the position of a black line using the read line function and sends the value Returns the last value computed if PID is running void send line position int message 1 unsigned int tmp_sensors 5 int line position if pid enabled line position last _proportional 2000 else line position read _line tmp_sensors IR_EMITTERS ON message 0 line position serial send blocking char message 2 10 Expansion Informati
54. is a series of pulses of varying width this method of speed control is called pulse width modulation PWM An example series of PWM pulses is shown in the graph at right as the size of the pulses decreases from 100 duty cycle down to 0 the motor speed decreases from full speed down to a stop PWM speed control showing gradual deceleration voltage V motor speed time ms In the 3pi speed control is accomplished using special PWM outputs of the main microcontroller that are linked to the internal timers Timer0 and Timer2 This means that you can set the PWM duty cycle of the two motors once and the hardware will continue to produce the PWM signal in the background without any further attention The set_motors function in the Pololu AVR Library see Section 6 a for more information lets you set the duty cycle and it uses 8 bit precision a value of 255 corresponds to 100 duty cycle For example to get 67 on M1 and 33 on M2 you would call set_motors 171 84 To get a slowly decreasing PWM sequence like the one shown in the graph you would need to write a loop that gradually decreases the motor speed over time Turning with a differential drive The 3pi has an independent motor and wheel on each side which enables a method of locomotion called differential drive It is also known as a tank drive since this is how a tank drives It is completely unlike the steering system of automobile which uses a single drive
55. lled TTL level The microcontroller and most of the circuitry in the 3pi operate at 5 V so voltage regulation is essential There are two basic types of voltage regulators Linear regulators use a simple feedback circuit to vary how much energy is passed through and how much is discarded The regulator produces a lower output voltage by dumping unneeded energy This wasteful inefficient approach makes linear regulators poor choices for applications that have a large difference between the input and output voltages or for applications that require a lot of current For example 15 V batteries regulated down to 5 V with a linear regulator will lose two thirds of their energy in the linear regulator This energy becomes heat so linear regulators often need large heat sinks and they generally don t work well with high power applications Switching regulators turn power on and off at a high frequency filtering the output to produce a stable supply at the desired voltage By carefully redirecting the flow of electricity switching regulators can be much more efficient than linear regulators especially for high current applications and large changes in voltage Also switching regulators can convert low voltages into higher voltages A key component of a switching regulator is the inductor which stores energy and smooths out current on the 3pi the inductor is the gray block near the ball 5 How Your 3pi Works Page 10 of 56 Pololu 3pi Robot User
56. llow segment c also contains a single function follow_segment which will drive 3pi straight along a line segment until it reaches an intersection or the end of the line This is almost the same as the line following code discussed in Section 7 but with extra checks for intersections and the ends of lines Here is the function void follow segment int last_proportional 0 long integral 0 while 1 Normally we will be following a line The code below is similar to the 3pi linefollower pid example but the maximum speed is turned down to 60 for reliability Get the position of the line unsigned int sensors 5 unsigned int position read line sensors IR EMITTERS ON The proportional term should be 0 when we are on the line int proportional int position 2000 Compute the derivative change and integral sum of the position int derivative proportional last proportional integral proportional Remember the last position last proportional proportional Compute the difference between the two motor power settings 8 Example Project 2 Maze Solving Page 31 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation ml m2 If this is a positive number the robot will turn to the left If it is a negative number the robot will turn to the right and the magnitude of the number determines the sharpness of the turn int power difference
57. llowing Page 23 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation sensors are working properly before starting the robot For more information on this and other LCD commands see Section 5 of the command reference http www pololu com docs 0J18 5 Waiting for the user to press a button It s very important for your robot not to start driving until you want it to start or it could unexpectedly drive off of a table or out of your hands when you are trying to program it We use the button_is_pressed function to wait for you to press the B button while displaying the battery voltage or sensor readings For more information on button commands see Section 8 of the command reference http www pololu com docs 0J18 In the second phase of the program your 3pi will take a sensor reading and set the motor speed appropriately based on the reading The general idea is that if the robot is off on either side it should turn to get back on but if it s on the line it should try to drive straight ahead The following steps occur inside of a while 1 loop which will continue repeating over and over until the robot is turned off or reset 1 The function read_line is called This takes a sensor reading and returns an estimate of the robot s position with respect to the line as a number between 0 and 4000 A value of 0 means that the line is to the left of sensor 0 value of 1000 means that the line is directly under sensor 1 20
58. loluQTRSensors cpp The code makes use of timer TCNT2 which is a special register in the AVR that we have configured to count up continuously incrementing every 0 4 us Basically the code waits until one of the sensors changes value counting up the elapsed time in the variable time It is important to use a separate variable for the elapsed time since the timer TCNT2 periodically overflows dropping back to zero Upon detecting a transition from a 1 to a 0 on one of the sensors by measuring a change in the input port PINC the code determines which sensor changed and records the time in the array sensor _values i After the time limit maxvalue is reached this is set to 2000 by default on the 3pi corresponding to 800 us the loop ends and the time values are returned 5 e 3pi Simplified Schematic Diagram A full understanding of how your 3pi works cannot be achieved without first understanding its schematic diagram 5 How Your 3pi Works Page 16 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Pololu 3pi Robot Simplified Schematic Diagram array R25b 1k and IR LED y programming MSA control R21 connection po R25a 1k 220 PE R26b 1k ANN Daa R26a 1k GREEN pos _R25a 1 x and user pushbultons 1 senaing circuit TB6612FNG motor driver and motors ae You can download a pdf version of the schematic here http www pololu com file download 3pi_schematic pdf file_id 0J119
59. motor and steerable front wheels Turning with a differential drive is accomplished by running the two motors at different speeds In the previous set_motors example the left wheel will spin faster than the right driving the robot forward and to the right The difference in speeds determines how sharp the turn will be and spinning in place can be accomplished by running one motor forward and one backward Spinning is an especially effective maneuver for a round robot and you won t have to worry about parallel parking 180 180 255 120 255 255 The 3pi demonstrating the effects of various motor settings 5 d Digital inputs and sensors The microcontroller at the heart of the 3pi an Atmel AVR megal68 has a number of pins which can be configured as digital inputs they are read by your program as a 1 or a 0 depending on whether the voltage is high above about 2 V or low Here is the circuit for one of the pushbutton inputs 5 How Your 3pi Works Page 14 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 15 3 PB1 gt R27 1k Normally the pull up resistor R 20 50 k brings the voltage on the input pin to 5 V so it reads as a 1 but pressing the button connects the input to ground 0 V through a 1 k resistor which is much lower than the value of R This brings the input voltage very close to 0 V so the pin reads as a 0 Without the pull up resistor the input would be floating when the button is
60. mum speed when no force is applied and a maximum torque when the motor is completely stopped We call these the free running speed and the stall torque Naturally a motor uses the least current when no force is applied to it and the current drawn from the batteries goes up until it stalls so the free running current and stall current are also important parameters characterizing the motor The stall current is usually much higher than the free running current as shown in the graph below 300 stall current J 4 5 free running speed E 200 107 3 g g 3 100 y 0 5 9 8 free running current 3 177 0 9 0 0 0 2 4 6 8 10 torque oz in Motor operation current and speed vs torque The free running speed of a small DC motor is usually many thousands of rotations per minute rpm much high than the speed we want the wheels of a robot to turn A gearbox is a system of gears that converts the high speed low torque output of the motor into a lower speed higher torque output that is a much better suited for driving a robot The gear ratio used on the 3pi is 30 1 which means that for every 30 turns of the motor shaft the output shaft turns once This reduces the speed by a factor of 30 and ideally increases the torque by a factor of 30 The resulting parameters of the 3pi motors are summarized in this table The 30 1 gearmotor used on the 3pi Gear ratio 30 1 Free running speed 700 rpm Free running current 60 mA Stall tor
61. n analog input When its shorting block is in place it controls the emitters for the IR sensors when its shorting block is removed the emitters are always on Pin ADC6 is a dedicated analog input that connects to a voltage divider circuit that monitors the 10 Expansion Information Page 54 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation battery voltage when its shorting block is in place and pin ADC7 is a dedicated analog input that connects to the user trimmer potentiometer when its shorting block is in place If you are willing to give up the LCD as is required when you use the expansion kit without cutouts http www pololu com catalog product 978 you gain access to several more I O lines Removing the LCD completely frees the three LCD control pins PBO PD2 and PD4 and it makes the four LCD data pins PB1 PB4 PBS and PD7 available for limited use If you do use the LCD data pins you must make sure that their alternate functions do not conflict with whatever you connect to them Pins PB1 PB4 and PBS connect to the user pushbuttons and PD7 connects to the green user LED It is important to note that PB4 and PBS are also programming lines so you must not connect anything here that would interfere with programming So in summary pins PDO and PD1 are completely free digital I O lines that can be used for general purpose I O or for TTL serial communciation Pins PC5 ADC6 and ADC7 can be freed from 3pi hardwa
62. need to readjust the parameters as the maximum speed increases By gradually increasing the maximum speed and tuning the parameters see if you can get your 3pi to run as fast as possible 7 Example Project 1 Line Following Page 29 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 8 Example Project 2 Maze Solving 8 a Solving a Line Maze The next step up from simple line following is to teach your 3pi to navigate paths with sharp turns dead ends and intersections Make a complicated network of intersecting black lines add a circle to represent the goal and you have a line maze which is a challenging environment for a robot to explore In a line maze contest robots travel as quickly as possible along the lines from a designated start to the goal keeping track of the intersections that they pass along the way Robots are given several chances to run the maze so that they can follow the fastest possible path after learning about all of the dead ends The mazes that we will teach you to solve in this tutorial have one special feature they have no loops That is there is no way to re visit any point on the maze without retracing your steps Solving this type of maze is much easier than solving a looped maze since a simple strategy allows you to explore the entire maze We ll talk about that strategy in the next section We also usually construct our mazes using only straight lines drawn on a regular grid but t
63. not pressed and the value read could be affected by residual voltage on the line interference from nearby electrical signals or even distant lightning Don t leave an input floating unless you have a good reason Since the pull up resistors are important they are included within the AVR the resistor R in the picture represents this internal pull up not a discrete part on the 3pi circuit board A more complicated use for the digital inputs is in the reflectance sensors Here is the circuit for the 3pi s leftmost reflectance sensor which is connected to pin PCO vec VBOOST PCO U4 The sensing element of the reflectance sensor is the phototransistor shown in the left half of U4 which is connected in series with capacitor C21 A separate connection leads through resistor R12 to pin PCO This circuit takes advantage of the fact the digital inputs of the AVR can be reconfigured as digital outputs on the fly A digital output presents a voltage of 5 V or 0 V depending on whether it is set to a 1 or a 0 by your program The way it works is that the pin is alternately set to a 5 V output and then a digital input The capacitor stores charge temporarily so that the input reads as a 1 until most of the stored charge has flowed through the phototransistor Here is an oscilloscope trace showing the voltage on the capacitor yellow dropping as its charge flows through the phototransistor and the resulting digital input value of
64. nter lt 20 counter gt 60 set_motors 40 40 else 7 Example Project 1 Line Following Page 26 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation set_motors 40 40 This function records a set of sensor readings and keeps track of the minimum and maximum values encountered The IR_EMITTERS ON argument means that the IR LEDs will be turned on during the reading which is usually what you want calibrate line sensors IR EMITTERS ON Since our counter runs to 80 the total delay will be 80 20 1600 ms delay ms 20 set_motors 0 0 Display calibrated values as a bar graph while button_is pressed BUTTON B Read the sensor values and get the position measurement unsigned int position read line sensors IR EMITTERS ON Display the position measurement which will go from 0 when the leftmost sensor is over the line to 4000 when the rightmost sensor is over the line on the 3pi along with a bar graph of the sensor readings This allows you to make sure the robot is ready to go clear print long position lcd_goto_xy 0 1 display readings sensors delay ms 100 Els ET clear print Go Play music and wait for it to finish before we start driving play from program space go while is playing This is the main function where the code starts All C programs must have a main function
65. o robot programming and it makes a great contest it s easy to build a line following course the rules are simple to understand and it s not hard to program your 3pi to follow a line Optimizing your program to make your 3pi zoom down the line at the highest speed possible however is a challenge that can introduce you to some advanced programming concepts Pololu 3pi robot on a 3 4 black line A great looking line following course can be constructed for a few dollars in a couple of hours at home For information on building your own course see our tutorial on Building Line Following and Line Maze Courses http www pololu com docs 0J22 7 b A Simple Line Following Algorithm for 3pi A simple line following program for the 3pi is available in the folder examples atmega168 3pi linefollower Note An Arduino compatible version of this sample program can be downloaded as part of the Pololu Arduino Libraries http www pololu com docs 0J17 see Section 5 g The source code demonstrates a variety of different features of the 3pi including the line sensors motors LCD battery voltage monitor and buzzer The program has two phases The first phase of the program is the initialization and calibration phase which is handled by the function intitialize This function is called once at the beginning of the main function before anything else happens and it takes care of the following steps 1 Calling pololu_3pi_init 2000 t
66. o set up the 3pi with the sensor timeout set to 2000x0 4 us 800 us This means that the sensor values will vary from 0 completely white to 2000 completely black where a value of 2000 indicates that the sensor s capacitor took at least 800 us to discharge 2 Displaying the battery voltage returned by the read_battery_millivolts function It is important to monitor battery voltage so that your robot does not surprisingly run out of batteries and shut down during the middle of a competition or during programming For more information see Section 3 of the command reference http www pololu com docs 0J18 3 Calibrating the sensors This is accomplished by turning the 3pi to the right and left on the line while calling the calibrate line _sensors function The minimum and maximum values read during this time are stored in RAM This allows the read_line_sensors_calibrated function to return values that are adjusted to range from 0 to 1000 for each sensor even if some of your sensors respond differently than the others The read_line function used later in the code also depends on having calibrated values For more information see Section 12 of the command reference http www pololu com docs 0J18 4 Displaying the calibrated line sensor values in a bar graph This demonstrates the use of the Icd_load_custom_character function together with print_character to make it easy to see whether the line 7 Example Project 1 Line Fo
67. on Page 46 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Sends the trimpot value 0 1023 void send trimpot int message 1 message 0 read_trimpot serial_send_blocking char message 2 Sends the batter voltage in millivolts void send battery millivolts int message 1 message 0 read_battery millivolts serial _send_blocking char message 2 Drives ml forward void ml_forward char byte read_next_byte if check data byte byte return set_ml_speed byte 127 255 byte 2 Drives m2 forward void m2_ forward char byte read_next_byte if check data byte byte return set_m2_speed byte 127 255 byte 2 Drives ml backward void ml_backward char byte read_next_byte if check_data_byte byte return set_ml_speed byte 127 255 byte 2 Drives m2 backward void m2_backward char byte read_next_byte if check_data_byte byte return set_m2_speed byte 127 255 byte 2 A buffer to store the music that will play in the background char music buffer 1001 Plays a musical sequence void do play unsigned char tune length read next byte if check data byte tune length return unsigned char i for i 0 i lt tune_length i if i gt sizeof music _buffer avoid overflow return 10 Expansion Information Page 47 of 56
68. ors to 0 0 and run the following command to loop forever while 1 7 c Advanced Line Following with 3pi PID Control A more advanced line following program for the 3pi is available in the folder examplestatmegal6813pi linefollower pid Note An Arduino compatible version of this sample program can be downloaded as part of the Pololu Arduino Libraries http vww pololu com docs 0J17 see Section 5 g O 2001 2009 Pololu Corporation The technique used in this example program known as PID control addresses some of the problems that you might have noticed with the previous example and it should allow you to greatly increase your robot s line following speed Most importantly PID control uses continuous functions to compute the motor speeds so that the jerkiness of the previous example can be replaced by a smooth response PID stands for Proportional Integral Derivative these are the three input values used in a simple formula to compute the speed that your robot should turn left or right The proportional value is approximately proportional to your robots position with respect to the line That is if your robot is precisely centered on the line we expect a proportional value of exactly 0 If it is to the left of the line the proportional term will be a positive number and to the right of the line it will be negative This is computed from the result returned by read_line simply by subtracting 2000 The integr
69. pin PCO blue The rate of current flow through the phototransistor depends on the light level so that when the robot is over a bright white surface the value returns to 0 much more quickly than when it is over a black surface The trace shown above was taken when the sensor was on the edge between a black surface and a white one this is what it looks like on pure white 5 How Your 3pi Works Page 15 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation The length of time that the digital input stays at 1 is very short when over white and very long when over black The function read line sensors in the Pololu AVR Library switches the port as described above and returns the time for each of the five sensors Here is a simplified version of the code that reads the sensors time 0 last time TCNT2 while time lt _maxValue Keep track of the total time This implicity casts the difference to unsigned char so we don t add negative values unsigned char delta time TCNT2 last time time delta time E last_time delta_time continue immediately if there is no change if PINC last _c continue save the last observed values last_c PINC figure out which pins changed for i 0 i lt _numSensors i if sensor values i sensor values i 0 amp amp register i amp bitmask i time This piece of code is found in the file src PololuQTRSensors Po
70. proportional 20 integral 10000 derivative 3 2 Compute the actual motor settings We never set either motor to a negative value const int max 60 the maximum speed if power difference gt max power difference max if power difference lt max power difference max if power difference lt 0 set_motors maxtpower difference max else set_motors max max power difference We use the inner three sensors 1 2 and 3 for determining whether there is a line straight ahead and the sensors 0 and 4 for detecting lines going to the left and right if sensors 1 lt 100 amp amp sensors 2 lt 100 amp amp sensors 3 lt 100 There is no line visible ahead and we didn t see any intersection Must be a dead end return else if sensors 0 gt 200 sensors 4 gt 200 Found an intersection return Between the PID code and the intersection detection there are now about six more parameters that could be adjusted We ve picked values here that allow 3pi to solve the maze at a safe controlled speed try increasing the speed and you will quickly run in to lots of problems that you ll have to handle with more complicated code Putting the C files and header files into your project is easy with AVR Studio In the left column of your screen you should see options for Source Files and Header Files Right click on either one and you will have the option to add or remove f
71. put and digital VO dedicated analog input dedicated analog input reset pushbutton 2001 2009 Pololu Corporation Notes Alternate Functions USART input pin RXD connected to red user LED high turns LED on USART output pin TXD external interrupt 0 INTO Timer2 PWM output B OC2B USART external clock input output XCK Timer0 external counter T0 Timer0 PWM output B OCOB Timer0 PWM output A OCOA connected to green user LED high turns LED on Timer input capture ICP 1 divided system clock output CLKO user pushbutton pressing pulls pin low Timer PWM output A OC1A Timer PWM output B OC1B Timer2 PWM output A OC2A ISP programming line user pushbutton pressing pulls pin low Caution also an ISP programming line user pushbutton pressing pulls pin low Caution also an ISP programming line drive high for 10 us then wait for line input to go low sensor labeled PCO leftmost sensor drive high for 10 us then wait for line input to go low sensor labeled PC1 drive high for 10 us then wait for line input to go low sensor labeled PC2 center sensor drive high for 10 us then wait for line input to go low sensor labeled PC3 drive high for 10 us then wait for line input to go low sensor labeled PC4 rightmost sensor jumpered to sensors IR LEDs driving low turns off emitters ADC input channel 5 ADCS jumpered to 2 3rds of battery voltage ADC input channel 6 ADC
72. que 6 ozin Stall current 540 mA 5 How Your 3pi Works Page 12 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation The two wheels of the 3pi each have a radius of 0 67 in which means that the maximum force 1t can produce with two motors when driving forward is 2x6 0 67 18 oz The 3pi weighs about 7 oz with batteries so the motors are strong enough to lift the 3pi up a vertical slope or accelerate it at 2 g twice the acceleration of gravity The actual performance is limited by the friction of the tires on a steep enough slope the wheels will slip before they stall in practice this happens when the slope is around 30 40 Driving a motor with speed and direction control One nice thing about a DC motor is that you can change the direction of rotation by switching the polarity of the applied voltage If you have a loose battery and motor you can see this for yourself by making connections one way and then turning the battery around to make the motor spin in reverse Of course you don t want take the batteries out of your 3pi and reverse them every time it needs to back up instead a special arrangement of four switches called an H bridge allows the motor to spin either backwards or forwards Here is a diagram that shows how the H bridge works If switches 1 and 4 are closed the center picture current flows through the motor from left to right and the motor spins forward Closing switches 2 and 3 ca
73. re by removing their respective shorting blocks PC5 can be used as an analog input or a digital I O and ADC6 and ADC7 are dedicated analog inputs Pins PBO PD2 and PD4 become completely free digital I O lines once you remove the LCD and pins PB1 PB4 PBS and PD7 are digital I O lines that you can use for certain applications if you are careful not to cause conflicts between them and their alternate functionality For more information please see Section 9 for the 3pi pin assignment tables and Section 5 e for the 3pi schematic diagram 10 Expansion Information Page 55 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 11 Related Resources To learn more about using the Pololu 3pi Robot see the following list of resources WinAVR http winavr sourceforge net AVR Studio http www atmel com avrstudio Pololu AVR Library Command Reference http www pololu com docs 0J18 detailed information about every function in the library e Programming the 3pi Robot from the Arduino Environment http www pololu com docs 0J17 a guide to programming the 3pi using the Arduino IDE in place of AVR Studio AVR Libc Home Page http www nongnu org avr libe ATmegal68 documentation http www atmel com dyn products product_card asp PN ATmega168 Tutorial AVR Programming on the Mac http bot thoughts blogspot com 2008 02 avr programming on mac html Finally we would like to hear your comments and que
74. s here 8 f Improving the Maze Solving Code We have gone over the most important parts of the code the other bits and pieces like the function display_path the start up sequence and calibration etc can be found with everything else in the folder examples 3pi mazesolver After you have the code working and you understand it well you should try to improve your robot to be as fast as possible There are many things you can do to try to make it better Increasing the line following speed Improving the line following PID constants Increasing turning speed Identifying situations where the robot has gotten lost Adjusting the speed based on what is coming up e g driving straight through an S at full speed 8 Example Project 2 Maze Solving Page 38 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation 9 Pin Assignment Tables optional user LEDs on pins PD1 and PD7 battery charger connector piezo buzzer on pin PB2 30 1 Micro es AAA Metal batteries Gearmotors not included optional power LED push on push off We power button ISP programming connector pin 1 removable 8x2 user pushbuttons character LCD on pins PB1 PB4 and PB5 General features of the Pololu 3pi robot top view integrated QTR RC reflectance sensors on digital pins PCO PC4 red user LED on pin PD1 green user LED on pin PD7 ATmega168 user microcontroller potentiometer running at 20 M
75. stions over at the 3pi Robot Group http forum pololu com viewforum php f 29 on the Pololu Robotics Forum http forum pololu com 11 Related Resources Page 56 of 56
76. t for Macs is limited You might find the following materials useful in creating an environment for your robot to explore e Several large sheets of white posterboard available at crafts or office supply stores or dry erase whiteboard stock commonly available at home construction supply stores e Light colored masking tape for joining multiple sheets together e 3 4 black electrical tape to create lines for your robot to follow 4 b Powering Up Your 3pi The first step in using your new 3pi robot is to insert four AAA batteries into the battery holders To do this you will need to remove the LCD Pay attention to the LCD s orientation as you will want to plug it back in this way when you are done With the LCD removed your 3pi should look like the picture to the right Once the batteries are in place you should return the LCD to its position over the rear battery holder Make sure each male LCD header pin goes into a corresponding female socket Next push the power button located on the left side of the rear battery pack to turn on your 3pi You should see the two blue power LEDs on the underside of the 3pi light and the 3pi should begin running its preloaded demo program You can simply push the power button again to turn the 3pi off and you can push the reset button located just below the power button to reset the program the robot is running 4 c Using the Preloaded Demo Program Your 3pi comes preloaded with a pro
77. t effect is that the robot is heading in its original direction again The path can be simplified to a 0 tum a single S The following diagram depicts this scenario showing the two functionally equivalent paths from start to end Left Back Left Straight Another example is a T intersection with a dead end on the left LBS The turns are 90 left 180 and 0 for a total of 90 right The sequence should be replaced with a single R In fact whenever we have a sequence like xBx we can replace all three turns with a turn corresponding to the total angle eliminating the U turn and speeding up our solution Here s the code to handle this Path simplification The strategy is that whenever we encounter a sequence xBx we can simplify it by cutting out the dead end For example LBL gt S because a single S bypasses the dead end represented by LBL void simplify path only simplify the path if the second to last turn was a B if path _ length lt 3 path path _length 2 B return gt int total angle 0 int i for i 1 1i1 lt 3 i switch path path_length i case R total_angle 90 break case L total _ angle 270 break case B total _ angle 180 break 8 Example Project 2 Maze Solving Page 35 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Get the angle as a number between 0 and 360 degrees
78. test c print Hello 1 Header Files play L16 ceg gt c External Dependencies 4 3 Other Files rd red_led 0 green_led 1 delay_ns 100 red_led 1 green_led 0 delay_ms 100 return 0 i gt gt El c Users paul Desktop libpololu avr examples simple test 3 4 Build yx E Build O Message A Find in Files 4 Breakpoints and Tracepoints AVR Studio showing the 3pi sample program To compile this program select Build gt Build or press F7 Look for warnings and errors indicated by yellow and red dots in the output displayed below If the program compiles successfully the message Build succeeded with 0 Warnings will appear at the end of the output and a file test hex will have been created in the examples simple test 3pi default folder 6 Programming Your 3pi Page 20 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Build started 15 7 2008 at 10 10 02 avr gcc exe mmcu atmegal68 Wall gdwarf 2 std gnu99 Os funsigne avr gcc exe mmcu atmegal68 W1 gc sections Wl Map test map test o avr objcopy 0 ihex R eeprom test elf test hex avr objcopy j eeprom set section flags eeprom alloc load cha avr objdump h S test elf gt test lss AVR Memory Usage Device atmegal68 Program 3190 bytes 19 5 Full text data bootloader Data 40 bytes 3 9 Full data bss noinit Build succeeded with 0 Warnings
79. tion and use of the 3pi IR sensors motor control bar graphs using custom characters and music playback making it a good starting point for developing your own more competitive line follower http www pololu com docs 0d21 http www pololu com http forum pololu com The 3pi include file must be at the beginning of any program that uses the Pololu AVR library and 3pi include lt pololu 3pi h gt LL include lt avr pgmspace h gt This include file allows data to be stored in program space The ATmegal68 has 16k of program space compared to 1k of RAM so large pieces of static data should be stored in program space Introductory messages The PROGMEM identifier causes the data to go into program space const char welcome linel PROGMEM Pololu const char welcome line2 PROGMEM 3 xf7 Robot const char demo name linel PROGMEM Line const char demo name line2 PROGMEM follower A couple of simple tunes stored in program space const char welcome PROGMEM gt g32 gt gt c32 const char go PROGMEM L16 cdegreg4 Data for generating the characters used in load_custom_characters and display_readings By reading levels starting at various offsets we can generate all of the 7 extra characters needed for a bargraph This is also stored in program space const char levels PROGMEM y 600000 600000 600000 600000 600000 6
80. total angle total_angle 360 Replace all of those turns with a single one switch total angle case 0 path path_ length 3 S break case 90 path path_length 3 R break case 180 path path_length 3 B break case 270 path path_length 3 L break The path is now two steps shorter path_length 2 One interesting point about this code is that there are some sequences that should never be encountered by a left turning robot like RBR which would be replaced by S according to this code In a more advanced program you might want to keep track of inconsistencies like this since they indicate some kind of a problem that could cause the robot to get lost Now let s step through a slightly more complicated maze showing how we can simplify the path as we explore it Fully explore the maze using a left hand on the wall strategy ESFSFB L AB L AL FBAL The above list of actions is a record of all the steps we took to fully explore the maze while looking for the end which is marked by the large black circle Our goal is to now reduce this list to represent the shortest path from start to finish by weeding out all of the dead ends One option is to perform this pruning when we finish the maze but the better approach is to perform the pruning as we go to keep our list from growing excessively large and taking up more memory than we have available Prune out the first
81. unsigned char found_right 0 Now read the sensors and check the intersection type unsigned int sensors 5 read_line sensors IR_EMITTERS_ ON Check for left and right exits if sensors 0 gt 100 found _left 1 if sensors 4 gt 100 found_right 1 Drive straight a bit more this is enough to line up our wheels with the intersection set_motors 40 40 delay ms 200 Check for a straight exit read _line sensors IR _EMITTERS_ON if sensors 1 gt 200 sensors 2 gt 200 sensors 3 gt 200 found straight 1 Check for the ending spot Tf all three middle sensors are on dark black we have solved the maze if sensors 1 gt 600 amp amp sensors 2 gt 600 amp amp sensors 3 gt 600 break Intersection identification is complete 1f the maze has been solved we can follow the existing path Otherwise we need to learn the solution unsigned char dir select turn found left found straight found right Make the turn indicated by the path turn dir Store the intersection in the path variable path path_length dir path_ length You should check to make sure that the path_length does not exceed the bounds of the array We ll ignore that in this example Simplify the learned path simplify path Display the path on the LCD display path We ll discuss the call to simplify_path in the next section Before
82. uses the current to reverse direction and the motor to spin backward An H bridge can be constructed with mechanical switches but most robots including the 3pi use transistors to switch the current electronically The H bridges for both motors on the 3pi are all built into a single motor driver chip the TB6612FNG and output ports of the main microcontroller operate the switches through this chip Here is a table showing how output ports PDS and PD6 on the microcontroller control the transistors of motor M1 PDS PD6 1 2 3 4 M1 0 0 off off off off off coast 0 1 off on on off forward 1 0 on off off on reverse 1 1 off off on on off brake Motor M2 is controlled through the same logic by ports PD3 and PB3 PD3 PB3 1 2 3 4 M2 0 0 off off off off off coast 0 1 off on on off forward 1 0 on off off on reverse 1 1 off off on on off brake 5 How Your 3pi Works Page 13 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation Speed control is achieved by rapidly switching the motor between two states in the table Suppose we keep PD6 high at 5 V also called a logical 1 and have PDS alternate quickly between low 0 V or 0 and high The motor driver will switch between the forward and brake states causing M1 to turn forward at a reduced speed For example if PD6 is high two thirds of the time a 67 duty cycle then M1 will turn at approximately 67 of its full speed Since the motor voltage
83. values read 10 characters if serial receive blocking buffer 10 100 break get the line position serial _send AxB6 1 int line position 1 if serial receive blocking char line position 2 100 break get the battery voltage serial _send AxB1 1 read 2 bytes O 2001 2009 Pololu Corporation 10 Expansion Information Page 53 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation int battery millivolts 1 if serial receive blocking char battery millivolts 2 100 break display readings display levels unsigned int buffer led_goto_xy 5 0 line position 0 4 to get it into the range of 0 1000 if line position 0 1000 line position 0 999 to keep it to a maximum of 3 characters print long line position 01 prine T AED lcd goto _xy 0 1 print long battery millivolts 0 print mV Ja delay ms 10 if button A is pressed increase motorl speed if button is pressed BUTTON A amp amp speedl lt 127 speedl else if speedl gt 1 speedl 2 else if speedl gt 0 speedl 0 if button C is pressed control motor2 if button is pressed BUTTON C amp amp speed2 lt 127 speed2 else if speed2 gt 1 speed2 2 else if speed2 gt 0 speed2 0 if button B is pressed do PID control if button is pressed BUTTON B slave _set_pid 40 1 20 3 2 else slave stop pid slave _set_motors
84. voltage stays the same but the maximum current output is multiplied by the number of batteries When they are connected in series with the positive terminal of one connected to the negative terminal of the next the maximum current stays the same while the voltage multiplies Either way the maximum power output will be multiplied by the number of batteries Think about two people using two buckets to lift water from a lake to higher ground If they stand next to each other working in parallel they will be able to lift the water to the same height as before while delivering twice the amount of water If one of them stands uphill from the other they can work together in series to life the water twice as high but at the same rate as a single person 5 How Your 3pi Works Page 9 of 56 Pololu 3pi Robot User s Guide O 2001 2009 Pololu Corporation In practice we only connect batteries in series This is because different batteries will always have slightly different voltages and if they are connected in parallel the stronger battery will deliver current to the weaker battery wasting power even when there is nothing else in the circuit If we want more current we can use bigger batteries AAA AA C and D batteries of the same type all have the same voltage but they can put out very different amounts of current The total amount of energy in any battery is limited by the chemical reaction once the chemicals are exhausted the battery will
85. will be based on AVR Studio For more general instructions on using the Pololu C C libraries with our AVR based robot boards including Linux installation instructions see the Pololu AVR C C Library User s Guide http www pololu com docs 0J20 Warning Do not attempt to program your 3pi if its batteries are drained or uncharged make sure you charge any new rechargeable batteries fully before you first use them Losing power during programming could permanently disable your 3pi 6 a Downloading and Installing the C C Library The Pololu C C AVR Library makes it easy for you to use the advanced features of your 3pi the library is used for all of the examples in the following sections For your convenience the source code for these examples and the demo program is included with the library To begin the installation process for the Pololu AVR C C Library you will need to download the zip file e Pololu AVR Library http www pololu com file download libpololu avr 090414 zip file_id 0J191 877k zip released 2009 04 14 Open the zip file and click Extract all to extract the Pololu AVR Library files A directory called libpololu avr will be created The automatic installation installs all Pololu AVR Library files in the location of your avr gcc installation This is done by running install bat or by opening a command prompt and typing make install If the automatic installation works you can proceed to Se

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