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WPI Robotics Library User`s Guide

1. Initialize the camera PCVideoServer pc The constructor starts the image server task o SECIS 7 Stop image server task EEGEN Restart task and serve images again Example 37 Sending images to the PC dashboard program To use this code with the LabVIEW dashboard the PC must be configured as IP address 10 x x 6 to correspond with the cRIO address 10 x x 2 Vision Image Processing Access to National Instrument s nivison library for machine vision enables automated image processing for color identification tracking and analysis The Vision APL cpp file provides open source C wrappers to a subset of the proprietary library The full specification for the simplified FRC Vision programming interface is in the FRC Vision API Specification document which is in the WindRiverldocslextensions FRC directory of the Wind River installation with this document The FRC Vision interface also includes high level calls for color tracking TrackingAPI cpp Programmers may also call directly into the low level library by including nivision h and using calls documented in the NI Vision for LabWindows CVI User Manual Naming conventions for the vision processing wrappers are slightly different from the rest of WPILib C routines prefixed with imaq belong to NI s LabVIEW CVI vision library Routines prefixed with frc are simplified interfaces to the vision library provided by BAE Systems for FIRST Robotics Competition use Sam
2. A C program that sets up the camera gets images and processes them Notice how the HSLImage object is used with the camera The camera supports video back to the dashboard When your dashboard program does a network connection to the PCVideoServer object on the robot a stream of JPEG images will be sent back to the dashboard The sample LabVIEW dashboard application will make connections to the video server and you will be able to see what the robot camera is seeing in real time as it is driving in your lab or in competition Once you retrieve an instance of the camera the server will be automatically available for video back to the dashboard You don t have to write any code to enable this Working with images There are a number of image classes that represent the types of images that are supported by the NI IMAQ Image Acquisition library For each image type there are methods that can be called to do various operations on the image Cascading these image operations together is the way to do more complex operations such as target recognition A good way to prototype image processing code is to use the NI Vision Assistant that is included with the FRC Software DVD Images taken with the FRC camera can be saved to disk Then using the Vision Assistant you can try different operations with varying parameters you set and will show the result of each operation You can cascade a number of image operations together and see the result of them co
3. 1f button number 2 pressed top f Have both right and left motors get input from the throttle axis leftControl Set driveJoy GetThrottle rightControl Set driveJoy GetAxis kThrottleAxis 1f button number 4 is pressed else if driveJoy GetRawButton 4 If button number 4 is pressed Have the left motor get input from the magnitude of the joystick s position leftControl Set driveJoy GetMagnitude Example 22 Using buttons to determine how to interpret the joystick inputs Enhanced I O through the Cypress Module There are additional I O options available through the Cypress module extended I O class The module contains An accelerometer Analog inputs Analog outputs A button A status LED Digital inputs Digital outputs PWM outputs Fixed digital output Encoder inputs with index Touch sensor PWM outputs All these are accessible through the DriverStationEnhancedIO class The class is a singleton i e there is never more than a single instance of it in the system You can get a reference to the class through the DriverStation object as shown DriverStationEnhancedIO amp dseio DriverStation GetInstance GetEnhancedIO Example 23 Getting a reference to the DriverStationEnhancedIO object in C tationEnhancedIO dseio tation getInstance getEnhancedIO Example 24 Getting a reference to the DriverStationEnhancedIO object in Java Once you have a reference to t
4. RA ARA 61 JA AA 62 INOUfIGaLOnu senectt AAH AA AA AA AA AMAG 62 System Archie D 64 Contributing to the WPI Robotics Library eese eene nnnm nnnnnnn teneas 65 Appendix A 2009 Camera and Vision u s 66 cnc P EA EE dE a 66 Camera task management saiast AA nisi NANA ANA AA 66 Camera sensor property configuration eeeeeeeeee nennen tentent tente ntnn Lr 66 Sensor property configuration using a text file sese erne 67 Simple Behrens rv 67 Configurable Camera initialization Laman tentatus dE Age ee a 68 mage ACQUIS TOM c iiaiai 68 Camera Mett pakana 69 mapaso erm ERU 69 Vision Image Process SE sean eser AA ABA inii d eee redii n iron ear Be nei i inii di tc KAHANI 69 Color Tracking P KAKANAN NAKAKAKAIN ANAN KAKA GAAN ANA ee 70 Example 1 Using Defaults mu aaa baci tipica tke Fac ABA 70 Example 2 Using Specified Ranges educ iie ANA aE 71 Example 3 Using Return Values eei nit nter etenim en rin LIRA 71 Example 4 Two Color Trac E 72 Stuff to do TODO redo Joe s pictures and get some better explanations TODO make the serial and 12C sections about communications TODO Find the comments in the Java and C forums about the documentation Using the WPI Robotics Library The WPI Robotics library WPILib is a set of software classes that interfaces with the hardware in your FRC robot s control system There are classe
5. SlotToIndex m slot readSelect Averaged false Synchronized sync m_registerWindowSemaphore m_module gt writeReadSelect readSelect amp status m_module gt strobeLatchOutput amp status value INT16 m_module gt readOutput amp status wpi_assertCleanStatus status return value This will take the semaphore declaring that this piece of code owns the associated data Access the data inside the block and when the block exits the synchronized object will be automatically freed by C and the semaphore will be released allowing access from other parts of your code You should use the same semaphore in all the places where you write code that access that protected data Timers Timers provide a means of timing events in your program For example your program can start a timer wait for an even to happen then read the timer value as a way of determine the elapsed time The Timer class can get the time value as well as start stop and reset the current time associated with that timer Notification There is a facility in WPILib to let you do regular timed operations The Notifier class will run a function that you write after a period of time or at regular intervals The function runs as a separate task and is started with optional context information An example is the PIDController class which requires calculations to be done on a regular basis It creates a Notifier object using the function to be
6. This is used to implement the GearTooth object with direction sensing e Semi period mode counts the period of a portion of the input signal This is used to measure the time of flight of the echo pulse in an ultrasonic sensor e Normal mode can count edges ofa signal in either up counting or down counting directions based on the input selected Encoders Encoders are devices for measuring the rotation of a spinning shaft Encoders are typically used to measure the distance a wheel has turned which can be translated into the distance the robot has traveled The distance traveled over a measured period of time represents the speed of the robot and is another common use for encoders The following table lists the WPILib supported encoder types Simple encoders Single output encoders that provide a state change as the Counter class wheel is turned With these encoders there is no way of detecting the direction of rotation The Innovation First VEX encoder and the index outputs of a quadrature encoder are examples of this type of device Quadrature Quadrature encoders have two outputs typically referred encoders to as the A channel and the B channel and are is out of Encoder class phase from each other Looking at the relationship between the two intputs provides information about the direction the motor is turning The relationship between the inputs is identified by locating the rising edge and falling edge signals The quadratur
7. about the sensor any necessary calibration or settings as well as an example of how to implement the sensors in your robot program The camera section also includes information about image processing and color tracking both commonly used with FRC robots The next primary section discusses actuators such as motors and pneumatics and is represented in the chart below Si Figure 3 WPILib Actuators section organization The actuator section describes different types of motor control and solenoid control including the use of speed controllers relays and solenoids The next section feedback is outlined in the chart below Figure 4 WPILib feedback section organization The second primary section of the user s guide is the feedback section This section talks about two different aspects user feedback and response This covers feedback data that you can get from the driver station including using buttons lights potentiometers and joysticks The miscellaneous section primarily discusses more advanced programming techniques used for control i e PID control multitasking in C and other select topics The structure of the control section is shown in the chart below Miscellaneous Control PID Multitasking Timing Figure 5 WPILib miscellaneous section organization Choosing Between C and Java C and Java are very similar languages in fact Java has its roots in C If you can write WPILib C programs for yo
8. class loading or unloading e Reflection a way of manipulating classes while the program is running is also not supported e The Java compiler generates a series of byte codes for the virtual machine When you create a program for the cRIO with Java ME a step is automatically run after the program compiles called pre verification This pre verification pass simplifies the program loading process and reduces the size of the Java virtual machine JVM e Finalization is not implemented meaning the system will not automatically call the finalize method of an unreferenced object If you need to be sure code runs when a class is no longer referenced you must explicitly call a method that cleans up e Java Native Interface JNI is not supported This is a method of calling C programs from Java using a standard technique e Serialization and Remote Method Invocation RMI are not supported The user interface APIs Swing and AWT are not implemented Threads are supported but thread groups are not Java ME is based on an earlier version of Java SE 1 3 so it doesn t include newer Java features such as generics annotations and autoboxing Sensors The WPI Robotics Library supports the sensors that are supplied in the FRC kit of parts as well as many other commonly used sensors available to F HST teams through industrial and hobby robotics outlets The WPILib supported sensors are listed in the chart below The supported sensors i
9. is very flexible and has a number of options that you might want to use to change the effectiveness of the detection The image above shows the previous image with the detected images shown in red You should refer to the sample programs included with C and Java and the National Instruments Vision library documentation for more information An example of ellipse detection in C and Java are shown here ColorImage image MonoImage luminancePlane image 5getLuminancePlane vector lt EllipseMatch gt results luminancePlane gt DetectEllipses amp ellipseDescriptor amp curveOptions NULL NULL printf Found d ellipses n results gt size delete luminancePlane Example 28 Ellipse detection taken from one of the C sample programs provided with the C FRC toolkit The luminance plane is extracted from the ColorImage producing a MonoImage The results of DetectEllipses is a vector of EllipseMatch structures with each one representing one detected ellipse lt java example of ellipse detection here gt Miscellaneous This section discusses more advanced control of your robot such as with PID programming The structure of this section is outlined in the chart below Miscellaneous Control PID Multitasking Timing Figure 21 Miscellaneous section organization PID Programming PID controllers are a powerful and widely used implementation of closed loop control The PIDController class allows fo
10. module provided in the kit has 32 GPIO lines Through the circuits in the digital breakout board these lines map into 10 PWM outputs 8 Relay outputs for driving Spike relays the signal light output an I2C port and 14 bidirectional GPIO lines The basic update rate of the PWM lines is a multiple of approximately 5 ms Jaguar speed controllers update at slightly over 5ms Victors update at slightly over 10ms and servos update at slightly over 20ms Higher update rates may be possible using the CAN bus and a community developed software available from http firstforge wpi edu Digital Inputs Digital inputs are generally used for controlling switches The WPILib DigitalInput object is typically used to get the current state of the corresponding hardware line 0 or 1 More complex uses of digital inputs such as encoders or counters are handled by using the appropriate classes Using these other supported device types encoder ultrasonic rangefinder gear tooth sensor etc doesn t require a digital input object to be created The digital input lines are shared from the 14 GPIO lines on each Digital Breakout Board Creating an instance of aDigitalInput object will automatically set the direction of the line to input Digital input lines have pull up resistors so an unconnected input will naturally be high If a switch is connected to the digital input it should connect to ground when closed The open state of the switch will be 1 and
11. of a two color target Note The FindTwoColors API code is in the demo project not in the WPILib project find a two color target ar Fincrreocolors wei cle ABOVE joel joe 1 Average the two particle centers to get center x amp y of combined tanger Dee enee geneet pariikcence ames 2 par2 center mass x normalized 2 SET eeler Leg enn oarl Center mass Y normaliLzecl q pak eener mass y aar a e Example 44 Finding a 2 color target To obtain the center of the combined target average the x and y values As before use the normalized values to work within a range of 1 0 to 1 0 Use the center_mass_x and center_mass_y values if the exact pixel position is desired Several parameters for adjusting the search criteria are provided in the Target h header file again provided in the TwoColorTrackDemo project not WPILib The initial settings for all of these parameters are very open to maximize target recognition Depending on your test results you may want to adjust these but remember that the lighting conditions at the event may give different results These parameters include e FRC MINIMUM PIXELS FOR TARGET default 5 Make this larger to prevent extra processing of very small targets e FRC ALIGNMENT SCALE default 3 0 scaling factor to determine alignment To ensure one target is exactly above the other use a smaller number However light shining directly on the target causes significant variat
12. real 15 digit precision EEJ Minor Radius double 64 bit real 15 digit precision EE Raw Score double 54 bit real 15 digit precision Uit Timestamp unsigned long 32 bit integer 0 to 4 294 967 295 2010 Camera and Image Processing New for 2010 there is a new API to access the camera and the related image processing classes Java implements the new API and the C library includes both the new and the old APIs Access to the camera and all the image types are now objects and can be accessed using methods on the appropriate object type Using the camera The camera is accessed through the AxisCamera class It is a singleton meaning that you can get an instance of the AxisCamera using the static method GetInstance in C or getInstance in Java Methods on the camera object can be used to set various parameters on the camera to programmatically control its operation Typically your robot program would retrieve image from the camera and process them Here is a portion of a program that retrieves images and performs some processing on them HSLImage image Create and set up a camera instance AxisCamera amp camera AxisCamera getInstance camera writeResolution k160x120 camera writeBrightness 0 Wait 3 0 loop getting images from the camera and finding targets while IsOperatorControl Get a camera image camera GetImage image image do something with image here Example 27
13. to the robot controller Teams are free to interface it themselves using the I2C class already built into WPILib Gyro Gyros typically in the FIRST kit of parts are provided by Analog Devices and are actually angular rate sensors The output voltage is proportional to the rate of rotation of the axis normal to the top package surface of the gyro chip The value is expressed in mV second degrees second or rotation expressed as a voltage By integrating summing the rate output over time the system can derive the relative heading of the robot Another important specification for the gyro is its full scale range Gyros with high full scale ranges can measure fast rotation without pinning the output The scale is much larger so faster rotation rates can be read but there is less resolution due to a much larger range of values spread over the same number of bits of digital to analog input In selecting a gyro you would ideally pick the one that had a full scale range that matched the fastest rate of rotation your robot would experience This would yield the highest accuracy possible provided the robot never exceeded that range Using the Gyro class The Gyro object should be created in the constructor of the RobotBase derived object When the Gyro object is used it will go through a calibration period to measure the offset of the rate output while the robot is at rest This requires that the robot be stationary and the gyro is unusable unt
14. 02 of analog output About 0 3V and about 100uA of drive current Button state Get the state of either the button on the board or 5 additional configurable buttons LED output Set the state of any of 8 LEDs Digital input Read digital input values for switches etc Digital output Set digital output lines PWM outputs 2 pairs of I O lines capable of PWM output There is a PWM generator for each pair Pairs have common periods but independent duty cycles Quadrature There are 2 signed 16 bit 4X quadrature encoder inputs with encoder input optional index functionality Capacitive touch There is a touch sensitive capacitive slider on the board slider Returns value between 0 1 with 1 indicating no touch Sending data to the dashboard Often itis desirable to get feedback from the robot back to the drivers The communications protocol between the robot and the driver station includes provisions for sending program specific data The program at the driver station that receives the data is called the dashboard A default dashboard program is supplied with the driver station The default dashboard program displays e Analog port values e Digital I O port values e Solenoids e Relays e Camera tracking data The data values are sent in groups called Clusters to correspond to the clusters on the LabVIEW dashboard program The data is sent in two groups high priority and low priority The high priority data is sent first then errors th
15. Encoders typically have a rotating disk with slots which spins in front of a photodetector As the slots pass the detector pulses are generated on the output The rate at which the slots pass the detector indicates the rotational speed of the shaft and the number of slots that have passed the detector indicates the number of rotations Below is a picture of an encoder mounted on a VEX robot Figure 12 A Grayhill quadrature optical encoder Note the two connectors one for the A channel and one for the B channel Quadrature Encoders Quadrature encoders are handled by the Encoder class Using a quadrature encoder is done by simply connecting the A and B channels to two digital I O ports and assigning them in the constructor for Encoder A diagram of the output signals of a quadrature encoder is shown below Chan nal Chan nal B Code track on disk Chan nel Channel B i je daa Figure 13 Quadrature encoder phase relationships between the two channels Some quadrature encoders have an extra index channel This channel pulses once for each complete revolution of the encoder shaft If counting the index channel is required for the application it can be done by connecting that channel to a simple Counter object which has no direction information There are four QuadratureEncoder modules in the cRIO s FPGA and 8 Counter modules that can operate as quadrature encoders One of the differences between the encoder and counter hardwa
16. TRASONIC tra SetAutomaticMode true t range ultra GetRangeInches Example 6 C example of creating an ultrasonic sensor object in automatic mode and getting the range trasonic ultra new Ultrasonic ULTRASONIC PING ULTRASONIC tra setAutomaticMode true t range ultra getRangeInches Example 7 Java example of creating an ultrasonic sensor object in automatic mode and getting the range Counter Subsystem The counters subsystem represents an extensive set of digital signal measurement tools for interfacing with many sensors There are several parts to the counter subsystem Below is a schematic representing the counter subsytem Figure 10 Schematic of the possible sources and counters in the Counter Subsystem in the cRIO Counters can be triggered by either Analog Triggers or Digital Inputs The trigger source can either control up down counters Counter objects quadrature encoders Encoder objects or interrupt generation Analog triggers count each time an analog signal goes outside or inside of a set range of voltages Counter Objects Counter objects are extremely flexible elements that can count input from either a digital input signal or an analog trigger They can operate in a number of modes based on the type of input signal some of which are used to implement other sensors in the WPI Robotics Library e Gear tooth mode enables up down counting based on the width of an input pulse
17. WPI Robotics Library User s Guide Worcester Polytechnic Institute Robotics Resource Center FIRST Brad Miller Ken Streeter Beth Finn Jerry Morrison Dan Jones Ryan O Meara Derek White Stephanie Hoag January 7 2010 Jan Brad Miller November 2009 Rev 1 0 Stephanie Hoag December 2009 Rev 2 0 Contents Ml Ero AA AA AA 6 Using the WPI Robotics Library aaa ca nant AAA C cada nk AR RR Sa iE RA IRAE AERA HERE aC ERR R 7 What is the WPI Robotics Library aaa aaa ap Aa a cute eae 7 Using the WPI Robotics Library User s Guide aaa an Ad 8 Choosing Between C and Java mmanannaaaaanaaaaaaaananaaaaaaaaa 11 Language DIUI AA AA 11 WPILID Differ ene Tr 12 Our version OL JAYA aaa EEGENEN 12 SEN SOS 14 Types of supported RE 14 Digital I O BAYANAN ANAKAN 15 Ee 15 Digital bru MC 16 Accelerometer 2009 panama ANAN ANAN 17 Accelerometer 2010 part me 18 GY EE 19 Using the Gyro DATA ANA AKIN AA 19 Setting the gyro e AA AA 19 HiT echnicCompass AA AA 22 Ultrasonic EE E 23 Counter Subas KANAN ANAKAN 25 Counter OU OCIS P AA 25 Encoder AA 25 Geart LOG SENIANG oma itu eai eda uto tu uua AA aan 26 jt T PANO 27 DUA e 28 Analog pug mma KANG 30 Analog Triggers AA AA 32 Controlling Actuators AAKALA 33 tee 33 Eelere 34 AT de 34 EEN 35 DO ci
18. bi SQ 35 Jb e AA M I 38 Usine the s rial por o eere oo gd rne cbr cutn inibi Bauen cel in XN RR Hue on dr NS 40 Er pA peret T APA REDE TREE RETE RUE EET IEEE 41 NEE E 42 COMP SONA NANA KALAN ANAN AA NAA NAAN AA 42 CP Object Ba E 43 els 43 Getting Feedback from the Driver Station essere 45 Getting Data from the Digital and Analog Dote EENEG 45 Other Driver Station Features aee tice utate aim edad MCI EE 46 1 Fe Y IS AA CRM 46 Enhanced I O through the Cypress Module Ae geg mtm tette treni lakes 49 Configuring the Enhanced HUT iscritte de seetdic tinte texit sex nig edt duse a t kd cnp irat 50 Enhanced NO data mana 50 Sending data to the dashboard Kama aa aaa eege Aerer 51 Adding dashboard data to your robot program eene tentent tentent 51 2010 Camera and Image Processing u s 53 Using the Calera Lama hin ana NANANA ANA a ANNA Maier ena len M ang lei 53 Working With mage P 53 Mat image MEMOLY enger EEN 54 IMAage Deg nanam 54 Common Color Image operations eeben 55 RE 55 Plane extraction and replacement aun ene desierto soin doni dl eire mdr i esce ku 57 Ellipse E e 57 Miscellaneous ees 59 PID Pro ran ryt M 59 Multitasking CC Lire 60 Creating t s ks Rn 60 Synchronizing TASKS AANI
19. byte 8 bit integer 0 to 255 RI GPIO unsigned word 16 bit integer 0 to 65535 IO GPIO OE unsigned word 16 bit integer 0 to 65535 Er PWM cluster of 10 elements a PWM 0 unsigned byte 8 bit integer 0 to 255 a PWM 1 unsigned byte 8 bit integer 0 to 255 a PWM 2 unsigned byte 8 bit integer 0 to 255 G5 PWM 3 unsigned byte 8 bit integer 0 to 255 a PWM 4 unsigned byte 8 bit integer 0 to 255 G5 PWM 5 unsigned byte 8 bit integer 0 to 255 a PWM 6 unsigned byte 8 bit integer 0 to 255 a PWM 7 unsigned byte 8 bit integer 0 to 255 a PWM 8 unsigned byte 8 bit integer 0 to 255 a PWM 9 unsigned byte 8 bit integer 0 to 255 98 Solenoid unsigned byte 8 bit integer 0 to 255 Data type of wire duster of 2 elements Tracking Data cluster of 4 elements BEd X double 64 bit real 15 digit precision Angle double 64 bit real 15 digit precision Angular Rate double 64 bit real 15 digit precision X double 64 bit real 15 digit precision Target Info duster of 2 elements C3 Targets 1 D array of duster of 2 elements Target Score double 64 bit real 15 digit precision Circle Descriptor cluster of 5 elements Er Position duster of 2 elements ET X single 32 bit real 6 digit precision E51 Y single 32 bit real 6 digit precision Angle double 64 bit real 15 digit precision EEJ Major Radius double 64 bit
20. called m controlLoop new Notifier PIDController CallCalculate this Then when it is time to start the function running in this case CallCalculate from the PIDController class it does it using the StartPeriodic method m controlLoop StartPeriodic m period The CallCalculate method will be called every m period seconds typically the period is a fraction of a second You can also have single instance notification the notifier function is only called one time after the interval using the StartSingle method Periodic notification can also be stopped by calling the Stop method on the Notifier System Architecture This section describes how the system is put together and how the libraries interact with the base hardware It should give you better insight as to how the whole system works and its capabilities Digital Sources Figure 22 Digital source breakdown Digital Filter Digital Pis Gier met GPIO PEE pl Exeeple erol 2 i e T a aa gre I i Mist erm a 1 mani aes i d NAA e T 1 ns 4 pi maja at m et ei n SC EES i d 1 bee S R i e Ag Figure 23 Digital filter diagram and example Contributing to the WPI Robotics Library TODO fill In this sction Appendix A 2009 Camera and Vision TODO the captions appear to be incorrect in this chapter Compare them with the original document and fix as necessary Camera The camera provided in the 2009 ki
21. cision Channel 1 single 32 bit real 6 digit precision Channel 2 single 32 bit real 6 digit precision Channel 3 single 32 bit real 6 digit precision Channel 4 single 32 bit real 6 digit precision Channel 5 single 32 bit real 6 digit precision Channel 6 single 32 bit real 6 digit precision Channel 7 single 32 bit real 6 digit precision cluster of 2 elements DigitalModule 0 typedef DigitalData ctl strict DigitalModule 0 cluster of 5 elements a Relay Fwd unsigned byte 8 bit integer 0 to 255 E Relay Rev unsigned byte 8 bit integer 0 to 255 E6 GPIO unsigned word 16 bit integer 0 to 65535 E GPIO OE unsigned word 16 bit integer 0 to 65535 PWM cluster of 10 elements Ca PWM 0 unsigned byte 8 bit integer 0 to 255 a PWM 1 unsigned byte 8 bit integer 0 to 255 G5 PWM 2 unsigned byte 8 bit integer 0 to 255 a PWM 3 unsigned byte 8 bit integer 0 to 255 G5 PWM 4 unsigned byte 8 bit integer 0 to 255 m PWM 5 unsigned byte 8 bit integer 0 to 255 a PWM 6 unsigned byte 8 bit integer 0 to 255 a PWM 7 unsigned byte 8 bit integer 0 to 255 a PWM 8 unsigned byte 8 bit integer 0 to 255 a PWM 9 unsigned byte 8 bit integer 0 to 255 DigitalModule 1 typedef DigitalData ctl strict DigitalModule 1 cluster of 5 elements mm Relay Fwd unsigned byte 8 bit integer 0 to 255 a Relay Rev unsigned
22. ct This file must be placed on the root directory of the cRIO Below is an example file Ha HE HEH HHH HTH HH E HE EE EE lines starting with or or comments this a sample configuration file only sensor properties may be set using this file set appearance properties when StartCameraTask is called Ha HEHE HH HH HH HH EE EE exposure auto colorlevel 99 Simple Camera initialization StartCameraTask initializes the camera to serve MJPEG images using the following camera appearance defaults e Frame Rate 10 frames sec e Compression 0 e Resolution 160x120 e Rotation 0 if StartCameraTask dprintf LOG ERROR Failed to spawn camera task Error code 3s GetErrorText GetLastError Example 32 C program showing how to initialize the camera Configurable Camera initialization Image processing places a load on the cRIO which may or may not interfere with your other robot code Depending on needed speed and accuracy of image processing it is useful to configure the camera for performance The highest frame rates may acquire images faster than your processing code can process them especially with higher resolution images If your camera mount is upside down or sideways adjusting the Image Rotation in the start task command will compensate and images will look the same as if the camera was mounted right side up Once the camera is initialized it begins saving images to an a
23. ds for setting oversampling and averaging on an analog to digital converter The number of averaged and oversampled values are always powers of two number of bits of oversampling averaging Therefore the number of oversampled or averaged values is two bits where bits is passed to the methods SetOversampleBits bits and SetAverageBits bits The actual rate that values are produced from the analog input channel is reduced by the number of averaged and oversampled values For example setting the number of oversampled bits to 4 and the average bits to 2 would reduce the number of delivered samples by 16x and 4x or 64 The sample rate is fixed per analog I O module so all the channels on a given module must sample at the same rate However the averaging and oversampling rates can be changed for each channel The WPI Robotics Library will allow the sample rate to be changed once for a module Changing it to a different value will result in a runtime error being generated The use of some sensors currently just the Gyro will set the sample rate to a specific value for the module it is connected to Analog Triggers Analog rage Rising El ENG Saki B3 Fly Rk Figure 16 Analog Trigger Jus Reject Filter ZPY simi be to Median filter es wr Samples only zg x omtpat point on bits N Y Figure 17 3 Point Average Reject Filter Controlling Actuators This section discusses the control of motors and pneumatics through spe
24. e edge of the sidecar labeled as output A while the reverse signal output is sent over the center pin labeled output B The final pin is a ground connection When a Relay object is created in WPILib its constructor takes a channel and direction or a slot channel and direction The slot is the slot number that the digital module is plugged into the digital module being what the digital sidecar is connected to on the cRIO this parameter is not needed if only the first digital module is being used The channel is the number of the connection being used on the digital sidecar The direction can be kBothDirections two direction solenoid kForwardOnly uses only the forward pin or kReverseOnly uses only the reverse pin If a value is not input for direction it defaults to kBothDirections This determines which methods in the Relay class can be used with a particular instance of the object The methods included in the relay class are shown in the table below void Set Value value This method sets the the state of the relay Valid inputs All Directions kOff turns off the Relay kForwardOnly or kReverseOnly kOn turns on forward or reverse of relay depending on direction kForwardOnly kForward set the relay to forward kReverseOnly kReverse set the relay to reverse void Sets the direction of the relay Valid inputs SetDirection Direction kBothDirections Allows the relay to use both the direction forward and re
25. e encoder class can look at all edges and give an oversampled output with 4x accuracy Gear tooth sensor The gear tooth sensor is typically supplied by FIRST as GearTooth class part of the FRC kit of parts It is designed to monitor the rotation of a sprocket or gear It uses a Hall effect device to sense the teeth of the sprocket as they move past the sensor Table 4 Encoder types that are supported by WPILib Gear Tooth Sensor Gear tooth sensors are designed to be mounted adjacent to spinning ferrous gear or sprocket teeth and detect whenever a tooth passes The gear tooth sensor is a Hall effect device that uses a magnet and solid state device that can measure changes in the field caused by the passing teeth The picture below shows a gear tooth sensor mounted on a VEX robot chassis measuring a metal gear rotation Notice that a metal gear is attached to the plastic gear The gear tooth sensor needs a ferrous material passing by it to detect rotation Figure 11 Gear tooth sensor with a ferrous gear cemented to the plastic Vex gear so the gear tooth senor would detect the rotation Encoders Encoders are devices for measuring the rotation of a spinning shaft Encoders are typically used to measure the distance a wheel has turned which can be translated into distance traveled by the robot Distance traveled over a measured period of time represents the speed of the robot and is another common measurement for encoders
26. ed controllers relays and WPILib methods The overall structure of this section is shown in the chart below Figure 18 Actuator section organization Motors The WPI Robotics library has extensive support for motor control There are a number of classes that represent different types of speed controllers and servos The WPI Robotics Library currently supports two classes of speed controllers PWM based motor controllers Jaguars or Victors and servos but is also designed to support non PWM motor controllers that will be available in the future In addition while not actually an actuator the RobotDrive class handles standard 2 motor 4 motor and Mecanum drive bases incorporating either Jaguar or Victor speed controllers Motor speed controllers take speed values in floating point numbers that range from 1 0 to 41 0 The value of 1 0 represents full speed in one direction 1 0 represents full speed in the other direction and 0 0 represents stopped Motors can also be set to disabled where the signal is no longer sent to the speed controller There are a number of motor controlling classes included in WPILib These classes are given in the table below Base class for all the pwm based speed controllers and servos Victor Speed controller with a 10ms update rate supplied by Innovation First commonly used in robotics competitions Jaguar Advanced speed controller used for 2009 and future FRC EES competi NN Servo Class designed t
27. en low priority data On any given update only the high priority data might get transmitted but on subsequent updates it might all get through In the default dashboard the camera data is sent as high priority and the port data is sent as low priority Adding dashboard data to your robot program There is a sample program called DashboardDataExample included with the Workbench and NetBeans distributions Look at those samples to get an idea of how to add custom data to your programs The data structures being sent correspond to the LabVIEW dashboard client program at the driver station Looking at the data model while looking at the sample program will make it clear as to how to customize the dashboard or write your own The left structure is the I O port data and the right structure is the camera tracking data Data type of wire Basic IO cluster of 3 elements cluster of 2 elements AnalogModule 0 cluster of 8 elements Channel 0 single 32 bit real 6 digit precision Channel 1 single 32 bit real 6 digit precision Channel 2 single 32 bit real 6 digit precision Channel 3 single 32 bit real 6 digit precision Channel 4 single 32 bit real 6 digit precision Channel 5 single 32 bit real 6 digit precision Channel 6 single 32 bit real 6 digit precision Channel 7 single 32 bit real 6 digit precision AnalogModule 1 cluster of 8 elements Channel 0 single 32 bit real 6 digit pre
28. eration of the Solenoid class by looking at the indicator lights on the 9472 module Solenoid s 8 Eus aane ak Of a lt Sa a s i new Solenoid i allocate the Solenoid objects foie obme 3b Of 3L Sp al s i gt Set true L coica ESTO om eve LONG tus sume i Op s lt Be is f s i 5Set false ZA cerca ehem cach Orn abi tu matake 1 59 P ang a Of a Bp ats s i gt Set true turn them back on in turn Wait 1 0 delete s i delete the objects Example 20 Controlling Solenoids in a C 4 program fragment Getting Feedback from the Driver Station The driver station is constantly communicating with the robot controller You can read the driver station values of the attached joysticks digital inputs analog inputs and write to the digital outputs In addition there is Enhanced I O provided through the Cypress module The DriverStation class has methods for reading and writing everything connected to it including joysticks There is another object Joystick that provides a more convenient set of methods for dealing with joysticks and other HID controllers connected to the USB ports The general relationships of feedback from the driver station are shown in the chart below The enhanced I O is provided through an additional class called DriverStationEnhancedIO This class has methods for reading and writing all the I O options on the Cypress module as well as configuring
29. essive blocking time the call will return unsuccessfully if a new image is not available in 0 5 second This is shown in the example below Image cameralmage frcCreatelmage IMAQ IMAGE HSL double timestamp timestamp of image returned double lastImageTimestamp timestamp of last image to ensure image is new int success GetImageBlocking cameralmage amp timestamp lastImageTimestamp Example 35 Getting images from the camera Camera Metrics Various camera instrumentation counters used internally may be accessed that may be useful for camera performance analysis and error detection Here is a list of the metrics CAM_STARTS CAM_STOPS CAM_NUM_IMAGE CAM_BUFFERS_WRITTEN CAM_BLOCKING_COUNT CAM_SOCKET_OPEN CAM_SOCKET_INIT_ATTEMPTS CAM_BLOCKING_TIMEOUT CAM_GETIMAGE_SUCCESS CAM_GETIMAGE_FAILURE CAM_STALE_IMAGE CAM_GETIMAGE_BEFORE_INIT CAM_GETIMAGE_BEFORE_AVAILABLE CAM READ JPEG FAILURE CAM PC SOCKET OPEN CAM PC SENDIMGAGE SUCCESS CAM PC SENDIMAGE FAILURE CAM PID SIGNAL ERR CAM BAD IMAGE SIZE CAM HEADER ERROR The following example call gets the number of images served by the camera EE Gec eamendetn e eAMIBNUMBMAGE Example 36 Retrieving the image number Images to PC The class PCVideoServer when instantiated creates a separate task that sends images to the PC for display on a dashboard application The sample program DashboardDemo shows an example of use StartCameraTask
30. ethods that can help with driving the robot either from the Driver Station controls or through programmed operations These methods are described in the table below Drive speed turn TankDrive leftStick rightStick ArcadeDrive stick HolonomicDrive magnitud e direction rotation SetLeftRightMotorSpeeds leftSpeed rightSpeed Designed to take speed and turn values ranging from 1 0 to 1 0 The speed values set the robot overall drive speed with positive values representing forward and negative values representing backwards The turn value tries to specify constant radius turns for any drive speed Negative values represent left turns and the positive values represent right turns Takes two joysticks and controls the robot with tank steering using the y axis of each joystick There are also methods that allow you to specify which axis is used from each stick Takes a joystick and controls the robot with arcade single stick steering using the y axis of the joystick for forward backward speed and the x axis of the joystick for turns There are also other methods that allow you to specify different joystick axes Takes floating point values the first two are a direction vector the robot should drive in The third parameter rotation is the independent rate of rotation while the robot is driving This is intended for robots with 4 Mecanum wheels independently controlled Takes two values for the left and right mot
31. g the WPI Robotics Library User s Guide This document is designed to help you use WPILib to program your robot The general architecture of the WPI Robotics Library documentation is shown below WPI Robotics Library Programming Hardware and environment control E Figure 1 WPILib Structure Flowchart As shown by the flowchart above the WPI Robotics Library supports environments for both the C and Java programming languages These environments and programming languages are discussed and explained in the Getting Started With Java For FRC and Getting Started With C For FRC documents Both of these documents along with other supportive materials can be found online at http first wpi edu in the FIRST Robotics Competition section The WPI Robotics Library User s Guide addresses the Hardware and Control branch of the WPILib structure A more detailed view of what this involves is shown in the series of charts below The first primary section of the user s guide is the sensors section This section discusses how to use the sensors provided in the FRC kit of parts as well as a few other sensors commonly used on FRC robots The structure of this section is shown in the chart below Sensors Vision system Accelerometer Gyro Compass Rangefinder Encoders Camera mage processing Figure 2 WPILib Sensors section organization As shown in the sensors flowchart above each sensor subsection includes basic information
32. he DriverStationEnhancedIO object you can call any of the methods that are available For example reading the touchpad slider is done with the following method assuming you already have an instance as described above double slider dseio GetTouchSlider Example 25 Getting the value of the touchpad slider on the Cypress module in C double slider dseio getTouchSlider Example 26 Getting the value of the touchpad slider on the Cypress module in Java Configuring the Enhanced I O The enhanced I O features of the Cypress module can be configured either e in your C or Java program e using the driver station I O configuration screen Fither way that the configuration is set the driver station records the configuration and remembers the settings Whenever the dashboard starts up it first reads the configuration file then the program settings are applied This makes it convenient to set up the dashboard using the control panel However programs counting on settings made on a specific dashboard won t work if the dashboard is swapped for another one Enhanced I O data The Enhanced I O module has a very powerful and expanded set of capabilities beyond just simple analog and digital I O Here are some ofthe available options Function Information Accelerometer Returns acceleration in Gs Analog inputs Analog inputs using a 3 3V reference either as a voltage or in ratiometric form Analog outputs 2 channels either A01 or A
33. he FPGA hardware also allows for interrupt processing to be dispatched at the task level instead of as kernel interrupt handlers reducing many common real time bug problems The WPI Robotics library does not explicitly support the C exception handling mechanism though it is available to teams for their programs Uncaught exceptions will unwind the entire call stack and cause the whole robot program to quit therefore we caution teams on the use of this feature In the Java version exceptions are used with the following conventions Checked exceptions Used in cases where runtime errors should be caught by the user program Library methods that throw checked exceptions must be wrapped in a try catch block Unchecked exceptions Used for cases like bad port numbers in initialization code that should be caught during the most basic testing of the program These don t require try catch blocks by the user program Objects are dynamically allocated to represent each type of sensor An internal reservation system for hardware is used to prevent reuse of the same ports for different purposes though there is a way around it if necessary In the C version the source code for the library will be published on a server for teams to review and make comments In the Java version the source code is included with each release There will also be a repository for teams to develop and share community projects for any language including LabVIEW Usin
34. he driver station analog and digital I O Other Driver Station Features The Driver Station is constantly communicating with the Field Management System FMS and provides additional status information through that connection bool IsDisabled Robot state bool IsAutonomous Field state autonomous vs teleop bool IsOperatorControl Field state UINT32 GetPacketNumber Sequence number of the current driver station received data packet Alliance red blue for the match Starting field position of the robot 1 2 or 3 float GetBatteryVoltage Battery voltage on the robot Table 11 Communicating with the FMS Joysticks The standard input device supported by the WPI Robotics Library is a USB joystick The 2009 kit joystick comes equipped with eleven digital input buttons and three analog axes and interfaces with the robot through the Joystick class The Joystick class itself supports five analog and twelve digital inputs which allows for joysticks with more capabilities The joystick must be connected to one of the four available USB ports on the driver station The startup routine will read whatever position the joysticks are in as the center position therefore when the station is turned on the joysticks must be at their center position The constructor takes either the port number the joystick is plugged into followed by the number of axes and then the number of buttons or just the port number from the d
35. he time between the transmission and the reception of the echo Below is a picture of the Devantech SRF04 with the connections labeled SRF04 4 MEL Connections 5v Supply Echo Pulse Output Trigger Pulse Input Do Not Connect Ov Ground Figure 9 SRF04 Ultrasonic Rangefinder connections Both the Echo Pulse Output and the Trigger Pulse Input have to be connected to digital I O ports on a digital sidecar When creating the Ultrasonic object specify which ports it is connected to in the constructor as shown in the examples below Ultrasonic ultra ULTRASONIC ECHO PULSE OUTPUT ULTRASONIC TRIGGER PULSE INPUT Example 4 C example of creating an ultrasonic rangefinder object Duett teen menu ER AS ONE UEERAS ONC mH CHOMP Vito Hm OUR Uni ULTRASONIC TRIGGER PULSE INPUT Example 5 Java example of creating an ultrasonic rangefinder object In this case ULTRASONIC ECHO PULSE OUTPUT and ULTRASONIC TRIGGER PULSE INPUT are two constants that are defined to be the digital I O port numbers Do not use the ultrasonic class for ultrasonic rangefinders that do not have these connections Instead use the appropriate class for the sensor such as an AnalogChannel object for an ultrasonic sensor that returns the range as a voltage The following two examples read the range on an ultrasonic sensor connected to the output port ULTRASONIC PING and the input port ULTRASONIC ECHO trasonic ultra ULTRASONIC PING UL
36. ightness 50 e whitebalance auto e exposure auto e exposurepriority auto e colorlevel 99 e sharpness 0 GetlmageSetting queries the camera image appearance properties see the Camera Initialization section below Examples of property configuration and query calls are below set a property ConfigureCamera whitebalance fixedfluorl query a sensorproperty char responseString 1024 create string engen eae sponse ee Zeta STEE if GetCameraSetting whitebalance responseString 1 printf no response from camera n else printf whitebalance s n responseString query an appearance property if GetlImageSetting resolution responseString 1 printf no response from camera n else printf resolution 3s n responseString Example 31 The example program CameraDemo cpp will configure properties in a variety of ways and take snapshots that may be FTP d from the cRIO for analysis Sensor property configuration using a text file The utility ProcessFile sets obtain camera sensor configuration specified from a file called cameraConfig txt on the cRIO ProcessFile is called the first time with 0 lineNumber to get the number of lines to read On subsequent calls each lineNumber is requested to get one camera parameter There should be one property value entry on each line i e exposure auto A sample cameraConfig txt file is included with the CameraDemo proje
37. il the calibration is complete Once initialized the GetAngle or getAngie in Java method of the Gyro object will return the number of degrees of rotation heading as a positive or negative number relative to the robot s position during the calibration period The zero heading can be reset at any time by calling the Reset reset in Java method on the Gyro object Setting the gyro sensitivity The Gyro class defaults to the settings required for the 80 sec gyro that was delivered by FIRST in the 2008 kit of parts To change gyro types call the SetSensitivity float sensitivity method or setSensitivity double sensitivity in Java and pass it the sensitivity in volts sec Take note that the units are typically specified in mV volts 1000 in the spec sheets For example a sensitivity of 12 5 mV sec would require a SetSensitivity setsensitivity in Java parameter value of 0 0125 The following example programs cause the robot to drive in a straight line using the gyro sensor in combination with the RobotDrive class The RobotDrive Drive method takes the speed and the turn rate as arguments where both vary from 1 0 to 1 0 The gyro returns a value indicating the number of degrees positive or negative the robot deviated from its initial heading As long as the robot continues to go straight the heading will be zero This example uses the gyro to keep the robot on course by modifying the turn parameter of the Drive meth
38. ion so this parameter is best left fairly high FRC MAX IMAGE SEPARATION default 20 Number of pixels that can exist separating the two colors Best number varies with image resolution It would normally be very low but is set to a higher number to allow for glare or incomplete recognition of the color FRC SIZE FACTOR default 3 Size difference between the two particles With this setting one particle can be three times the size of the other FRC MAX HITS default 10 Number of particles of each color to analyze Normally the target would be found in the first largest particles Reduce this to increase performance Increase it to maximize the chance of detecting a target on the other side of the field FRC COLOR TO IMAGE PERCENT default 0 001 One color particle must be at least this percent of the image
39. it mha Figure 19 Feedback section organization Getting Data from the Digital and Analog Ports Building a driver station with just joysticks is simple and easy to do especially with the range of HID USB devices supported by the Microsoft Windows based driver station Custom interfaces can be constructed and implemented using the digital and analog I O on the driver station Switches can be connected to the digital inputs the digital outputs can drive indicators and the analog inputs can read various sensors like potentiometers Here are some examples of custom interfaces that are possible e Set of switches to set various autonomous modes and options e Potentiometers on a model of an arm to control the actual arm on the robot e Rotary switches with a different resistor at each position to generate unique voltage to effectively add more switch inputs e Three pushbutton switches to set an elevator to one of three heights automatically These custom interfaces often give the robot better control than is available from a standard joystick or controller You can read write the driver station analog and digital I O using the following DriverStation methods connected to port channel bool GetDigitalIn UINT32 channel Read a digital input value nene w ponehal void SetDigitalOut UINT32 channel Write a digital output value bool GetDigitalOut UINT32 channel Read the currently set digital M uu pea pai co Table 10 Using t
40. jects internally to read the pressure switch and operate the Spike relay For example suppose you had a compressor and a Spike relay connected to Relay port 2 and the pressure switch connected to digital input port 4 Both of these ports are connected to the primary digital input module You could create and start the compressor running in the constructor of your Robot Base derived object using the following 2 lines of code Compressor c new Compressor 4 2 G SSicaucic 2 Example 18 Starting the compressor in a C program fragment In the example above the variable c is a pointer to a compressor object and the object is allocated using the new operator If it were allocated as a local variable in the constructor at the end of the constructor function its local variables would be deallocated and the compressor would stop operating C Object Life Span You need the Compressor object to last the entire match If you allocate it with new the best practice is to store the pointer in a member variable then delete it in the Robot s destructor as shown in the example below class RobotDemo public SimpleRobot f Compressor jm EE EE EE bue e RobotDemo MeCOMpRe SSO Ge EE EE EE m compressor Start Jj RobotDemo f geletefm Compressor Example 19 Making the compressor run for the entire match in a C program Alternatively you can declare it as a member object then initialize and start i
41. le angle set servo to angle Wait 1 0 wait 1 second Example 13 C example that rotates a servo through its full range in 10 steps RobotDrive The RobotDrive class is designed to simplify the operation of the drive motors based on a model of the drive train configuration The idea is to describe the layout ofthe motors Then the class can generate all the speed values to operate the motors for different situations For cases that fit the model it provides a significant simplification to standard driving code For more complex cases that aren t directly supported by the RobotDrive class it may be subclassed to add additional features or not used at all First create a RobotDrive object specifying the left and right Jaguar motor controllers on the robot as shown below RobotDrive drive 1 2 left right motors on ports 1 2 Example 14 Creating a Robot drive object in C or Java Or RobotDrive drive 1 2 3 4 four motor drive configuration Example 15 Creating a robot drive object with 4 motors This sets up the class for a 2 motor configuration or a 4 motor configuration There are additional methods that can be called to modify the behavior of the setup SetInvertedMotor kFrontLeftMotor true Example 16 Inverting the motor direction in C This sets the operation of the front left motor to be inverted This might be necessary depending on the setup of your drive train Once set up there are m
42. mage object using the threshold ranges shown You can see how the values are taken from the Vision Assistant window above Plane extraction and replacement There are a number of methods that will extract a single plane from a color image The meaning of the plane will depend on the type of the image For example in a RGB red green blue image the second plane is the green plane and represents all the green values In an HSL image the second plane is the saturation value for the image You can extract any type of plane from any type of image For example if you have an RGBImage object you can still extract the luminance plane by calling the GetLuminancePlane method in C or the getLuminancePlane method in Java b Ef Above are two images the first a color image taken with the camera on the robot as recorded by the driver station The second image was produced by extracting the luminance plane from the first image leaving only greyscale Ellipse detection Ellipse detection is one type of shape detection available for use with the camera Ellipse detection is a single IMAQ library call even though internally it does many steps to find ellipses This method is available on MonoImage objects Detecting ellipses from camera images that are color either RBGImage or HSLImage require extraction of a single plane Typically the luminance plane is used since it makes the detection less effected by color changes Ellipse detection
43. mbined Once it is working on a number of test images then it is easy to write the corresponding code and add it to your robot program Here is an example of cascading a Color Threshold and a Particle Analysis te ep1 Original Image Color Threshold 1 Partide Analysis 1 Al All of the sample images shown in this section were produced using the Vision Assistant Use of image memory In Java images are stored using C data structures and only pointers are manipulated all the actual processing is done at the C C level for optimum performance For example a threshold operation on a color image it is actually performed by C code and the image itself is stored as a C data structure This is to prevent unnecessary copies from C C to Java for large image structures In C the actual IMAQ image is stored as a member of the corresponding image object Whenever new images are produced as a result of an operation for example returning a BinaryImage as the result of a threshold operation a pointer BinaryImage is returned from the C method It is the responsibility of the caller to free the newly allocated image when finished with it Be sure to delete the image objects when you are finished using them See the example programs supplied with the C FRC Toolkit for more information Image types There are a number of image types available each used for a different purpose RESI ColorImage Monolmage HSLImage RGBImage Bina
44. nce provides Checks for array subscripts out of bounds uninitialized references to objects and other runtime errors that might occur in program development Compiles to byte code for a virtual machine and must be interpreted WPILib Differences In order to streamline transitions between C and Java all WPILib classes and methods have the same names in both languages There are some minor differences between the language conventions and utility functions These differences are detailed in the table below Method naming Upper case first letter and Lower case first letter and convention camel case after camel case thereafter e g GetDistance e g getDistance Utility functions Call function Library functions are e g Wait 1 0 will wait for implemented as methods one second e g Timer delay 1 0 will wait for one second Table 2 Java C Differences within WPILib Our version of Java The Java virtual machine and implementation used with WPILib is the Squawk platform based on the Java ME micro edition platform Java ME is a simplified version of Java designed for the limitations of embedded devices As a result there are no user interface classes or other classes that are not meaningful in this environment The most common Java platform is the Java Standard Edition SE Some of the SE features that are not included in our version of Java are described in the list below e Dynamic class loading is not supported for
45. nclude those that are provided in the FIRST kit of parts as well as other commonly used sensors Accelerometer Gyro Compass Rangefinder Encoders Camera Image processing Figure 6 WPILib sensor section Vision system Types of supported sensors On the cRIO the FPGA implements all the high speed measurements through dedicated hardware ensuring accurate measurements no matter how many sensors and motors are added to the robot This is an improvement over previous systems which required complex real time software routines The library natively supports sensors of the categories shown below Wheel motor Gear tooth sensors encoders analog encoders and position potentiometers measurement Robot orientation Compass gyro accelerometer ultrasonic rangefinder Generic pulse output Table 3 List of Supported Sensors There are many features in the WPI Robotics Library that make it easy to implement sensors that don t have prewritten classes For example general purpose counters can measure period and count from any device generating output pulses Another example is a generalized interrupt facility to catch high speed events without polling and potentially missing them Digital UO Subsystem Below is a visual representation of the digital sidecar and the digital I O subsystem D i Sit Car Ix 9 lt P pisi IL PH 2 ipd pats 14 et Z TY SI Figure 7 Digital I O Subsystem Diagram The NI 9401 digital 1 O
46. nels can be optionally oversampled and averaged to provide the value that is used by the program There are raw integer and floating point voltage outputs available in addition to the averaged values The diagram below outlines this process Figure 14 Analog Input System When the system averages a number of samples the division results in a fractional part of the answer that is lost in producing the integer valued result Oversampling is a technique where extra samples are summed but not divided down to produce the average Suppose the system were oversampling by 16 times that would mean that the values returned were actually 16 times the average Using the oversampled value gives additional precision in the returned value The oversample and average engine equations are shown below oversample bits average bits kl al 7 l Y CHAL D a AveAl ab o F p Jp oy LM AN Figure 15 Oversample and Average Engine Equations To set the number of oversampled and averaged values use the methods in the examples below void SetAverageBits UINT32 bits UINT32 GetAverageBits void SetOversampleBits UINT32 bits UINT32 GetOversampleBits Example 10 C methods for setting oversampling and averaging on an analog to digital converter void setAverageBits int bits UINT32 getAverageBits void setOversampleBits UINT32 bits UINT32 getOversampleBits Example 11 Java metho
47. o control small hobby servos as typically supplied bili T RobotDrive General purpose class for controlling a robot drive train with either 2 or 4 drive motors It provides high level operations like turning It does this by controlling all the robot drive motors in a coordinated way It s useful for both autonomous and tele operated driving Table 5 Types of motor control PWM The PWM class is the base class for devices that operate on PWM signals and is the connection to the PWM signal generation hardware in the cRIO It is not intended to be used directly on a speed controller or servo The PWM class has shared code for Victor Jaguar and Servo subclasses that set the update rate deadband elimination and profile shaping of the output signal Victor The Victor class represents the Victor speed controllers provided by Innovation First They have a minimum 10ms update period and only take a PWM control signal The minimum and maximum values that will drive the Victor speed control vary from one unit to the next You can fine tune the values for a particular speed controller by using a simple program that steps the values up and down in single raw unit increments You need the following values from a victor and the light on the Victor goes to full green Center The value that is in the center of the deadband that turns off AA o t direction Min The minimum value highest speed in opposite direction where the motors sto
48. od The angle is multiplied by Kp to scale it for the speed of the robot drive This factor is called the proportional constant or loop gain Increasing Kp will cause the robot to correct more quickly but too high and it will oscillate Decreasing the value will cause the robot correct more slowly maybe never getting back to the desired heading This is known as proportional control and is discussed further in the PID control section of the advanced programming section class GyroSample public SimpleRobot f RobotDrive myRobot robot drive system eor e Cy CO EE EE pubike GyroSample xal 2 ame ehe sensors Aangann Ia Sie Groe GL f GetWatchdog SetExpiration 0 1 void Autonomous gyro Reset while IsAutonomous GetWatchdog Feed float angle gyro GetAngle get heading myRobot Drive 1 0 angle Kp turn to correct heading Wait 0 004 myRobot Drive 0 0 0 0 ZA BECO zobot Example 1 A C program example to drive in a straight line using a gyro package edu wpi first wpilibj templates import edu wpi first wpilibj Gyro import edu wpi first wpilibj RobotDrive import edu wpi first wpilibj SimpleRobot import edu wpi first wpilibj Timer public class GyroSample extends SimpleRobot private RobotDrive myRobot robot drive system private Gyro gyro double Kp 0 03 public GyroSample getWatchdog setExpiration 0 1 protected
49. of scaling Joysticks in C The scaled value can then be used to change the setpoint of the control loop as the joystick is moved The 0 1 0 001 and 0 0 values are the Proportional Integral and Differential coefficients respectively The AnalogChannel object is already a subclass of PIDSource and returns the voltage as the control value and the Jaguar object is a subclass of PIDOutput Joystick turretStick 1 Jaguar turretMotor 1 AnalogChannel turretPot 1 PIDController turretControl 0 1 0 001 0 0 amp turretPot amp turretMotor turretControl Enable start calculating PIDOutput values while IsOperator turretControl SetSetpoint turretStick GetX 1 0 2 5 Wait 02 wait for new joystick values Example 30 Using the PIDController object The PIDController object will automatically in the background e Read the PIDSource object in this case the turretPot analog input e Compute the new result value e Set the PIDOutput object in this case the turretMotor This will be repeated periodically in the background by the prDcontroller The default repeat rate is 50ms although this can be changed by adding a parameter with the time to the end of the PIDController argument list See the reference document for details Multitasking C There are a number of classes in the C version of WPILib to aid in creating programs that use concurrent programming techniques The underlying ope
50. or speeds As with all the other methods this will control the motors as defined by the constructor Table 7 C options for driving a robot The Java methods are the same except with leading lower case characters The Drive method of the RobotDrive class is designed to support feedback based driving Suppose you want the robot to drive in a straight line despite physical variations in its parts and external forces There are a number of strategies but two examples are using gear tooth sensors or a gyro In either case an error value is generated that tells how far from straight the robot is currently tracking This error value positive for one direction and negative for the other can be scaled and used directly with the turn argument of the Drive method This causes the robot to turn back to straight with a correction that is proportional to the error the larger the error the greater the turn By default the RobotDrive class assumes that Jaguar speed controllers are used To use Victor speed controllers create the Victor objects then call the RobotDrive constructor passing it pointers or references to the Victor objects rather than port numbers Example TODO Relays The cRIO provides the connections necessary to wire IFI spikes via the relay outputs on the digital breakout board The breakout board provides a total of sixteen outputs eight forward and eight reverse The forward output signal is sent over the pin farthest from th
51. own in the example below The following declarations in the class are used for the example RobotDrive myRobot RengekekeehHue censet ecm Tm Example 40 C program declarations This is the initialization of the RobotDrive object the camera and the colors for tracking the target It would typically go in the RobotBase derived constructor if StartCameraTask 1 printf Failed to spawn camera task Error code 3s GetErrorText GetLastError myRobot new RobotDrive 1 2 values for tracking a target may need tweaking in your environment greenHue minValue 65 greenHue maxValue 80 greenSat minValue 100 greenSat maxValue 255 greenLum minValue 100 greenLum maxValue Zap Example 41 C program showing the use of return values Here is the code that actually drives the robot in the autonomous period The code checks if the color was found in the scene and that it was not too big close and not too small far If it is within the limits the robot is driven forward full speed 1 0 and with a turn rate determined by the center mass x normalized value of the particle analysis report The center mass x normalized value is 0 0 if the object is in the center of the frame otherwise it varies between 1 0 and 1 0 depending on how far off to the sides it is That is the same range as the Drive method uses for the turn value If the robot is correcting in the wrong direction then sim
52. p changing speed Table 6 Necessary information about Victors With these values call the setBounds method on the created Victor object void SetBounds INT32 max INT32 deadbandMax INT32 center INT32 deadbandMin WINES mt p Example 12 A C method for setting the bounds on a Victor object Jaguar The Jaguar class supports the Texas Instruments Jaguar speed controller It has an update period of slightly greater than 5ms and currently uses only PWM output signals In the future the more sophisticated Jaguar speed controllers might have other methods for control of its many extended functions The input values for the Jaguar range from 1 0 to 1 0 for full speed in either direction with 0 representing stopped Use of limit switches TODO Example TODO Servo The Servo class supports the Hitechnic servos supplied by F RST They have a 20ms update period and are controlled by PWM output signals The input values for the Servo range from 0 0 to 1 0 for full rotation in one direction to full rotation in the opposite direction There is also a method to set the servo angle based on the currently fixed minimum and maximum angle values For example the following code fragment rotates a servo through its full range in 10 steps Servo servo 3 float servoRange servo GetMaxAngle servo GetMinAngle for float angle servo GetMinAngle angle x servo GetMaxAngle angle servoRange 10 0 servo SetAng
53. ple programs provided include SimpleTracker which in autonomous mode tracks a color and drives toward it VisionServoDemo which also tracks a color with a two servo gimbal VisionDemo demonstrates other capabilities including storing a JPEG image to the cRIO and DashboardDemo sends images to the PC Dashboard application Image files may be read and written to the cRIO non volatile memory File types supported are PNG JPEG JPEG2000 TIFF AIDB and BMP Images may also be obtained from the Axis 206 camera Using the FRC Vision API images may be copied cropped or scaled larger smaller The intensity measurement functions available include calculating a histogram for color or intensity and obtaining values by pixel Contrast may be improved by equalizing the image Specific color planes may be extracted Thresholding and filtering based on color and intensity characteristics are used to separate particles that meet specified criteria These particles may then be analyzed to find the characteristics Color Tracking High level calls provide color tracking capability without having to call directly into the image processing routines You can either specify a hue range and light setting or pick specific ranges for hue saturation and luminance for target detection Example 1 Using Defaults Call GetTrackingData with a color and type of lighting to obtain default ranges that can be used in the call to FindColor The ParticleAnalysisReport retu
54. ply negate the turn value Example 4 Two Color Tracking An example of tracking a two color target is in the demo project TwoColorTrackDemo The file Target cpp in this project provides an API for searching for this type of target The example below first creates tracking data while IsAutonomous if FindColor IMAQ HSL amp greenHue amp greenSat amp greenLum spar amp amp par particleToImagePercent MAX PARTICLE TO IMAGE PERCENT amp amp par particleToImagePercent MIN PARTICLE E TO IMAGE PERCENT EE EE EE EE else myRobot gt Drive 0 0 0 0 Wait 0 05 myRobot gt Drive 0 0 0 0 Example 42 Autonomous color tracking and driving the robot towards the target PINK Spin TeL meme ELNIKI 2 tdl hue minValue 220 tdl hue maxValue 255 tdl saturation minValue 75 tdl saturation maxValue 255 tdl luminance minValue 85 tdl luminance maxValue 255 EEN sprint Ed name GREEN td2 hue minValue 55 td2 hue maxValue 125 s s td2 saturation minValue 58 td2 saturation maxValue 255 td2 luminance minValue 92 td2 luminance maxValue 255 Example 43 Typical color values for the green and pink targets Call FindTwoColors with the two sets of tracking data and an orientation ABOVE BELOW RIGHT LEFT to obtain two ParticleAnalysisReports which have details
55. r a PID control loop to be created easily and runs the control loop in a separate thread at consistent intervals The PIDController automatically checks a PIDSource for feedback and writes to a PIDOutput every loop Sensors suitable for use with PIDController in WPILib are already subclasses of PIDSource Additional sensors and custom feedback methods are supported through creating new subclasses of PIDSource Jaguars and Victors are already configured as subclasses of PIDOutput and custom outputs may also be created by sub classing PIDOutput The following example shows how to create a PIDController to set the position of a turret to a position related to the x axis on a joystick This turret uses a single motor on a Jaguar and a potentiometer for angle feedback As the joystick X value changes the motor should drive to a position related to that new value The PIDController class will ensure that the motion is smooth and stops at the right point A potentiometer that turns with the turret will provide feedback of the turret angle The potentiometer is connected to an analog input and will return values ranging from 0 5V from full clockwise to full counterclockwise motion of the turret The joystick X axis returns values from 1 0 to 1 0 for full left to full right We need to scale the joystick values to match the 0 5V values from the potentiometer This can be done with the following expression UE eelere tU zb 1 0 25 5 Example 29 Example
56. rating system VxWorks has a full support for multitasking but the classes simplify programming for the more common cases Creating tasks A task is a thread of execution in a program that runs concurrently with other tasks in a program Each task has a number of attributes including a name and priority Tasks share memory with each other To create a task you write a function that should is the starting point for that thread of execution Using the Task class you can run that function as a separate task Creating an instance of Task looks like this Task myTask taskname FUNCPTR functionToStart The task name will be seen in the task list in Workbench when you are debugging the program The functionToStart is the name of a function to run when the task is started FUNCPTR is a typedef that defines the type signature of the function The task is started using the Start method myTask Start Once started the function will run asynchronously along with the other tasks in the system Synchronizing tasks Starting tasks is easy and for many cases that s all that s required A good example is the Compressor class The compressor class creates a task that simply loops checking the pressure switch and operating the compressor relay It doesn t interact with other tasks and doesn t really share data with the rest of the program The difficulties with multitasking come in when there is data that s shared between two tasks If one ta
57. re is that encoders can give an oversampled 4X count using all 4 edges of the input signal but counters can only return a 1X or 2X result based on one of the input signals If 1X or 2X is chosen in the Encoder constructor a Counter module is used with lower oversampling If 4X default is chosen then one of the four FPGA encoders is used In the example below 1 and 2 are the port numbers for the two digital inputs and true tells the encoder to not invert the counting direction The sensed direction could depend on how the encoder is mounted relative to the shaft being measured The k4X makes sure that an encoder module from the FPGA is used and 4X accuracy is obtained To get the 4X value you should use the Get Raw method on the encoder The Get method will always return the normalized value by dividing the actual count obtained by the 1X 2X or 4X multiplier Encoder encoder 1 2 true k4X Example 8 C code creating an encoder on ports 1 and 2 with reverse sensing and 4X encoding Encoder encoder encoder new Encoder 1 2 true EncodingType k4X Example9 Java code craeating an encoder on ports 1 and 2 with reverse sensing and 4X encoding Analog Inputs The NI 9201 Analog to Digital module has a number of features not available on simpler controllers It will automatically sample the analog channels in a round robin fashion providing a combined sample rate of 500 ks s 500 000 samples second These chan
58. rea of memory accessible by other programs The images are saved both in the raw JPEG format and in a decoded format Image used by the NI image processing functions An example is shown below int frameRate 15 valid values O 30 int compression 0 valid values 0 100 ImageSize resolution k160x120 li IAGORL2O 9205240 154054090 ImageRotation rot ROT 180 f BOT O BOT L StartCameraTask frameRate compression resolution rot Example 33 C program showing how to save images Image Acquisition Images of types IMAQ IMAGE HSL IMAQ IMAGE RGB and IMAQ IMAGE US gray scale may be acquired from the camera To obtain an image for processing first create the image structure and then call GetImage to get the image and the time that it was received from the camera double timestamp timestamp of image returned Image cameralmage frcCreatelmage IMAQ IMAGE HSL if cameralmage printf error s GetErrorText GetLastError if GetlImage cameralmage amp timestamp printf error s GetErrorText GetLastError Example34 Getting images from the camera GetImage reads the most recent image regardless of whether it has been previously accessed Your code can check the timestamp to see if it s an image you already processed Alternatively GetImageBlocking Will wait until a new image is available if the current one has already been served To prevent exc
59. river s station The former is primarily for use in sub classing For example to create a class or a non kit joystick and the latter for a standard kit joystick The following example would create a default joystick called driveJoy on USB port 1 of the driver station Something like a Microsoft Sidewinder joystick which has five analog axes and eight buttons which would be a good candidate for a subclass of Joystick Joystick driveJoy 1 JOVSELG eeler Aromi Example 21 Creating a default Joystick object There are two methods to access the axes of the joystick Each input axis is labeled as the X Y Z Throttle or Twist axis For the kit joystick the applicable axis are labeled correctly a non kit joystick will require testing to determine which axes correspond to which degrees of freedom Each of these axes has an associated accessor the X axis from driveJoy in the above example could be read by calling driveJoy GetX the twist and throttle axes are accessed by driveJoy GetTwist anddriveJoy GetThrottle respectively Alternatively the axes can be accessed via the the GetAxis and GetRawAxis methods GetAxis takes an AxisType kXAxis kYAxis kZAxis kTwistAxis orkThrottleAxis and returns that axis value GetRawAxis takes a number 1 6 and returns the value of the axis associated with that number These numbers are reconfigurable and are generally used with custom control systems since the other
60. rned by FindColor specifies details of the largest particle of the targeted color TrackingThreshold tdata GetTrackingData BLUE FLUORE ParticleAnalysisReport par ge Hindeollor IMAOMHSM St datae tda tamat uration amp tdata luminance amp par f penal TO wal Bie se Sil Wo Ka Paka centerimaso xa nommelalZed para center massiy Oma Ee printf color as percent of image d par particleToImagePercent Example 38 Color tracking example The normalized center of mass of the target color is a range from 1 0 to 1 0 regardless of image size This value may be used to drive the robot toward a target Example 2 Using Specified Ranges To manage your own values for the color and light ranges you simply create Range objects as shown in the example below Range hue sat lum hermina iue badge Hue hue maxValue 155 sat minValue 100 Saturation sat maxValue 2557 lum minValue 40 Luminance lum maxValue 255 FindColor IMAQ HSL amp hue amp sat slum spar Example 39 Using specified ranges of colors to limit the found color values Tracking also works using the Red Green Blue RGB color space however HSL gives more consistent results for a given target Example 3 Using Return Values Here is an example program that enables the robot to drive towards a green target When it is too close or too far the robot stops driving Steering like this is quite simple as sh
61. ryImage This shows the hierarchy diagram of the types of images and the class relationships between them Image is the base class for all other image types If provides height and width accessor methods that work across all image types ColorImage is the basic color image type and can either be a HSLImage or an RGBImage representing the two most commonly used image formats ColorImage objects have three planes each representing some part of the total image In an RGBImage the three planes represent the red green and blue values that make up the total picture MonoImage objects represent a single color BinaryImage objects have a single bit for each pixel They are often the result of a color or edge detection operation on a Colorimage For example looking for objects of a particular color might use a threshold operation on a ColorImage resulting in a BinaryImage with each set pixel corresponding to a pixel in the ColorImage Common Colorlmage operations Once you have a ColorImage either HSLImage or RGBImage there are a number of operations that can be done it Most of these operations results in a new image of the same size Threshold detection Threshold detection takes a three ranges corresponding to the three color planes in the image type A BinaryImage is returned where each pixel that is on in the BinaryImage corresponds to a pixel in the ColorImage that was within the threshold range Locating color targets from the 2009 Lunac
62. s system charged by using a pressure switch and software to turn the compressor on and off as needed Table 9 Classes for controlling pneumatics Compressor The Compressor class is designed to operate the FRC supplied compressor on the robot A Compressor object is constructed with 2 input output ports e The Digital output port connected to the Spike relay that controls the power to the compressor A digital output or Solenoid module port alone doesn t supply enough current to operate the compressor e The Digital input port connected to the pressure switch that monitors the accumulator pressure The Compressor class will automatically create a task that runs in the background twice a second and turns the compressor on or off based on the pressure switch value If the system pressure is above the high set point the compressor turns off If the pressure is below the low set point the compressor turns on To use the Compressor class create an instance of the Compressor object and use theStart method This is typically done in the constructor for your Robot Program Once started it will continue to run on its own with no further programming necessary If you do have an application where the compressor should be turned off possibly during some particular phase of the game play you can stop and restart the compressor using the Stop and Start methods The compressor class will create instances of the DigitalInput and Relay ob
63. s to handle sensors motors the driver station and a number of other utility functions such as timing and field management What is the WPI Robotics Library The National Instruments compact RIO 9074 real time controller or cRIO for short is currently the robot controller provided by the FIRST Robotics Competition FRC It provides about five hundred times more memory than previous FRC controllers Dedicated FPGA hardware capable of sampling across 16 channels replaces previously cumbersome programming techniques necessary with previous controllers The WPI Robotics library is designed to e Work with the cRIO controller e Handle low level interfacing of components e Allow users of all experience levels access to experience appropriate features C and Java are the two choices of text based languages available for use on the cRIO These languages were chosen because they represent a better level of abstraction for robot programs than previously used languages The WPI Robotics Library is designed for maximum extensibility and software reuse with these languages The library contains classes which support the sensors speed controllers driver station and other hardware in the kit of parts In addition WPILib supports many commonly used sensors which are not in the kit such as ultrasonic rangefinders WPILib has a generalized set of features such as general purpose counters to provide support for custom hardware and devices T
64. sk is writing to the data and gets half of it written then the reader task starts up it will find inconsistent data Only half of the data will have been changed and that can cause very hard to track down problems in your code An example is the Camera class It s reading camera images in one task and your program is consuming them in a different task If the consumer tries to read an image while the camera is writing it half the image will be new and the other half will be old Not a good situation VxWorks provides a facility to help this called a Semaphore Semaphores let you synchronize access to data ensuring that only one task will have access to it at a time You lock the block of data read or write it then unlock it While it s locked any other task trying to access it will have to wait until it s unlocked WPILib has a class called Synchronized that simplifies the use of semaphores for this purpose It is modeled after the Java style of synchronization The model for synchronizing data access is to first create a semaphore that will be used Here is an example from the AnalogModule class in WPILib static SEM ID m registerWindowSemaphore Then to protect access to data using the semaphore create a new block with a Synchronized object on the first line INT16 AnalogModule GetValue UINT32 channel INT16 value CheckAnalogChannel channel tAI tReadSelect readSelect readSelect Channel channel 1 readSelect Module
65. t in the Robot s constructor In this case you need to use the constructor s nitialization list to initialize the Compressor object The C compiler will quietly give RobotDemo a destructor that deletes the Compressor object In Java you would accomplish the same thing as follows TODO add Java example here Solenoid The Solenoid object controls the outputs of the NI 9472 Digital Output Module It is designed to apply an input voltage to any of the 8 outputs Each output can provide up to 1A of current The module is designed to operate 12v pneumatic solenoids used on FIRST robots This makes the use of relays unnecessary for pneumatic solenoids The NI 9472 Digital Output Module does not provide enough current to operate a motor or the compressor so relays connected to Digital Sidecar digital outputs will still be required for those applications The port numbers on the Solenoid class range from 1 8 as printed on the pneumatics breakout board The NI 9472 indicator lights are numbered 0 7 for the 8 ports which is different numbering than used by the class or the pneumatic bumper case silkscreening Setting the output values of the Solenoid objects to true or false will turn the outputs on and off respectively The following code fragment will create 8 Solenoid objects initialize each to true on and then turn them off one per second Then it turns them each back on one per second and deletes the objects You can observe the op
66. t is the Axis 206 The C camera API provides initialization control and image acquisition functionality Image appearance properties are configured when the camera is started Camera sensor properties can be configured with a separate call to the camera which should occur before camera startup The API also provides a way to update sensor properties using a text file on the cRIO PcVideoServer cpp provides a C API that serves images to the dashboard running on a PC There is a sample dashboard application as part of the LabVIEW distribution that can interface with C and C programs Camera task management A stand alone task called FRC Camera is responsible for initializing the camera and acquiring images It continuously runs alongside your program acquiring images It needs to be started in the robot code if the camera is to be used Normally the task is left running but if desired it may be stopped The activity of image acquisition may also be controlled for example if you only want to use the camera in Autonomous mode you may either call StopCameraTask to end the task or call StoplmageAcquisition to leave the task running but not reading images from the camera Camera sensor property configuration ConfigureCamera sends a string to the camera that updates sensor properties GetCameraSetting queries the camera sensor properties The properties that may be updated are listed below along with their out of the box defaults e br
67. the closed state will be 0 In Java digital input values are true and false So an open switch is true and a closed switch is false Digital Outputs Digital outputs are typically used to run indicators or to interface with other electronics The digital outputs share the 14 GPIO lines on each Digital Breakout Board Creating an instance of a Digi talOutput object will automatically set the direction of the GPIO line to output In C digital output values are 0 and 1 representing high 5V and low 0V signals In Java the digital output values are true 5V and false OV Accelerometer 2009 part The two axis accelerometer provided in the kit of parts shown in the picture below is a two axis accelerometer This device can provide acceleration data in the Xand Y axes relative to the circuit board In the WPI Robotics Library you treat it as two separate devices one for the X axis and the other for the Y axis This provides better performance if your application only needs to use one axis The accelerometer can be used as a tilt sensor actually measuring the acceleration of gravity In this case turning the device on the side would indicate 1000 milliGs or one G Figure 8 FRC supplied 2 axis accelerometer board connected to a robot Accelerometer 2010 part The 2010 accelerometer is not currently available as a built in class but we expect it will be available shortly after the kickoff It will operate using the I2C interface
68. two methods reliably return the same data for a given axis There are three ways to access the top button defaulted to button 2 and trigger button 1 The first is to use their respective accessor methods GetTop and GetTrigger which return a true or false value based on whether the button is currently being pressed A second method is to call GetButton which takes a ButtonType which can be either kTopButton or kTriggerButton The last method is one that allows access to the state of every button on the joystick GetRawButton This method takes a number corresponding to a button on the joystick see diagram below and return the state of that button Figure 20 Diagram of a USB joystick In addition to the standard method of accessing the Cartesian coordinates x and y axes of the joystick s position WPILib also has the ability to return the position of the joystick as a magnitude and direction To access the magnitude the GetMagnitude method can be called and to access the direction either GetDirectionDegrees orGetDirectionRadians can be called See the example below Joystick driveJoy 1 Jaguar leftControl 1 Jaguar rightControl 2 if driveJoy GetTrigger If the trigger is pressed Have the left motor get input from Y axis and the right motor get input from X axis leftControl Set driveJoy GetY rightControl Set driveJoy GetAxis kXAxis else if driveJoy GetRawButton 2
69. ur robot then you can probably also write WPILib Java programs There are however reasons for choosing on programming language over the other Language Differences There is a detailed list of the differences between C and Java on Wikipedia available here http en wikipedia org wiki Comparison of Java and C Below is a summary of the differences that will most likely effect robot programs created with WPILib Memory allocated and freed manually Pointers references and local instances of objects Header files and preprocessor used for including declarations in necessary parts of the program Implements multiple inheritance where a class can be derived from several other classes combining the behavior of all the base classes Does not natively check for many common runtime errors Highest performance on the platform because it compiles directly to machine code for the PowerPC processor in the cRIO Table 1 Java C Difference Summary Objects must be allocated manually but are freed automatically when no references remain References to objects instead of pointers All objects must be allocated with the new operator and are referenced using the dot operator e g gyro getAngle Header files are not necessary and references are automatically resolved as the program is built Only single inheritance is supported but interfaces are added to Java to get the most benefits that multiple inherita
70. verse pins on the channel kForwardOnly Allows relay to use only the forward signal pin kReverseOnly Allows relay to use only the reverse signal pin Table 8 Relay class methods In the example below m relay is initialized to be on channel 1 Since no direction is specified the direction is set to the default value of kBothDirections m relay2 is initialized to channel 2 with a direction of kForwardOnly In the following line m relay is set to the direction of kReverseOnly and is then turned on which results in the reverse output being turned on m relay2 is then set to forward since it is a forward only relay this has the same effect as setting it toon After that m relay is turned off a command that turns off any active pins on the channel regardless of direction lay m relay 1 lay m relay2 2 Relay kForwardOnly Wn elen 5 Sete D een sein bellas o enee ees ec m relay Ser else elm p m relay2 Set Relay kForward m relay Set Rellen 8 BOE p Example 17 C example of controlling relays using the Relay class Using the serial port Using 12C Pneumatics Controlling pneumatics with WPILib is quite simple The two classes you will need are shown in the table below Solenoid Can control pneumatic actuators directly without the need for an additional relay In the past a Spike relay was required along with a digital output port to control a pneumatics component Compressor Keeps the pneumatic
71. void Autonomous gyro reset while isAutonomous getWatchdog feed double angle gyro getAngle get heading myRobot drive 1 0 angle Kp drive to heading Timer delay 0 004 myRoboc drive 0m0 MOKONG SEO olo Example 2 Java program example to drive in a straight line using a gyro HiTechnicCompass The compass uses the earth s magnetic field to determine the heading This field is relatively weak causing the compass to be susceptible to interference from other magnetic fields such as those generated by the motors and electronics on your robot If you decide to use a compass be sure to mount it far away from interfering electronics and verify tits accuracy Additionally the compass connects to the I2C port on the digital 1 O module It is important to note that there is only one I2C port on each of these modules HiTechnicCompass compass 4 compVal compass GetAngle Example 3 A C program to create a compass on the I2C port of the digital module plugged into slot 4 Ultrasonic rangefinder The WPI Robotics library supports the common Devantech SRF04 or Vex ultrasonic sensor This sensor has two transducers a speaker that sends a burst of ultrasonic sound and a microphone that listens for the sound to be reflected off of a nearby object It requires two connections to the cRIO one that initiates the ping and the other that tells when the sound is received The Ultrasonic object measures t
72. y game consists of finding the pink and green targets and making sure they were one over the other in the right order Using a threshold operation to detect only the pink portion of the image is done using a set of values that correspond to the pink color found on the targets The result is a bitmap BinaryImage that represents the pixel locations in the original images that represent the matching colors Image ColorImage operation This is the original image taken using the FRC camera This is the resultant bitmap with just the pixels that matched the pink threshold values One of the easiest ways to determine the threshold values is using the Vision assistant You can tune the 6 color parameters to find a set that results in the best discrimination of the image being tested Then those parameters can be copied into your program to do the detection in the robot Here you can see graphs that represent the values of Hue Saturation and Luminance in the original color image and the min max values that are the parameters to the threshold operation You can manipulate the values to see the effectiveness of the parameters changing The code to do this threshold operation is shown below Threshold pinkThreshold 226 255 28 255 96 255 HSLImage targetImage new HSLImage testImage png create image BinaryImage pinkPixels targetImage 5thresholdHSL pinkThreshold This code produces a BinaryI

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