the pennsylvania state university schreyer honors college
Contents
1. bID 1 b 200 512 calculate position writeword bID P_GOAL_POSITION_L pos issue position command if Carraytotal gt trun tstep 5 3 180 IF statement for starting to f take data load arraypos bID Identifying data with servo load arraypos 1 Readword bID P_PRESENT_SPEED_L read value from servo load arraypos 2 Readword bID P_PRESENT_POSITION_L arraypos 3 arraytotal 3 t tstep Milisec 50 for bID 6 bID lt 17 bID wheel stop command Writeword bID P_GOAL_SPEED_L 0 TxDStringC r n press start to recieve data r n incase the user is still connected MiliSec 1000 bkey WaitButtonChange allow user time to reattach robot for data collection TxDStringC r nbID t Speed t Position r n set up table for data output arraytotal 0 om arraytotal lt 179 oop for outputting the data TxDword10 C eaten eee X TXDString t TxDword10 load arraytotal 1 TxDStringC t TxDword10 Toad arraytotal 2 TxDStringC r n arraytotal 3 LEDOff BIT_LED_PLAY return 0 end program Page 232. trun 80 tstep 0 5 break case BIT_SW_RT TxDStringC RIGHT 200 break default used to catch incorrect choices eee r Incorrect button pressed Press another button reak LEDOff BIT_LED_PROG turn off program LED arraytotal trun tstep 5 3 set up total number of data points word load 180 set up array for data collection arraytotal 0 arraypos 0 MiliSec 1000 ae r n Variables set remove serial cable and press START to begin rogram bey nar eueeanciandeG allow user to disconnect and start program LEDOn BIT_LED_PLAY MiliSec 1000 TxDStringC r n variables calculated r n for bID 6 bID lt 17 bID 360 deg spin wheel mode initialize if Readword bID P_CCW_ANGLE_LIMIT_L 0 writeWord bID P_CCW_ANGLE_LIMIT_L TxDStringC r nwheels Initialized r n for bID 6 bID lt 16 wheel speed command to left side writeword bID P_GOAL_SPEED_L wspeed bID 2 TxDStringC r n left side turn command given r n a bID 7 bID lt 17 wheel speed command to right side writeword bID P_GOAL_SPEED_L cwspeed bID 2 TxDStringC r n right side turn command given r n r bID 1 bID lt 5 bID set speed for joint servos Writeword bID P_GOAL_SPEED_L jspeed Page 22 for t 1 t lt trun run for time duration for bID 1 bID lt 5 bID command loop for joint servos pos a sin w t
3. a command it is important to be able to switch rapidly between the serial ports and so the CM 5 was chosen In order to communicate with the AX 12 servos a specific data packet must be sent with instructions This packet includes complex formatting and calculations Page 6 Through many attempts the exact way of communicating with the servos was determined using a MATLAB based program for control as well as the Arduino However each section of the data packet needed to be calculated and precisely sent In contrast the CM 5 was specifically designed to operate the servos and includes open source libraries of custom commands that can be utilized This library must be included in the C language compiler in this case WinAVR that is used to program the board in order to utilize the commands The Arduino is also programmed in the C language however the commands are designed for the inputs and outputs of the CM 5 including the serial hardware switch These included commands make programming the robot much easier and less frustrating Another perk of the CM S that is worth mentioning is the wireless capability The board includes a space to solder a ZIG 100 wireless communication module which can be used with the CM 5 s custom library of commands to control the robot wirelessly from a PC or to allow the robot to communicate with another CM 5 The communication module uses ZigBee communication which is a simpler version of Bluetooth While not
4. an inclined ramp to test for ratchet holding strength After the incline the snake was tested in its sinusoidal mode with both powered wheels and unpowered wheels to test for joint feedback and snake motion similar to the previously created robot Through these tests the robot was tested to ensure proper operation and its capability to test experimental snake dynamics Train mode test Putting the robot into a straight train mode is as easy as setting the amplitude variable equal to zero and running the powered wheel simulation Once the test was underway the robot performed as expected All 12 wheels were turning at the assigned speed and the joints were holding in a straight line Upon completion of the test the robot was reconnected and the feedback data proved that the controller had successfully retrieved and stored wheel load and speed A small portion of the feedback data can be seen in figure 11 Page 14 Dynamixel Current Current ID Speed Load RPM 11 51 4 920 12 52 6 1103 13 55 4 992 14 50 8 1135 15 51 8 928 Figure 11 Feedback data from the straight train test After the flat surface test the robot was placed on a 30 degree incline to test ratchet holding strength Throughout the test the ratchets held just fine As the degree of incline was increased to 40 the robot began to slip due to loss of friction as well as well as some ratchet failure This test was only in the straight lin
5. model Suggestions for Future Work For future versions of this project several changes could be made that could improve the performance and capability of the robot First the ratchets worked well for the materials that were available but could be made better However the professionally made metal ratchets are still too expensive In the future the ratchets should be drawn up on a CAD program and cut out with a water jet or other rapid prototyping machine Properly angled teeth on a ratchet would cut down on rolling resistance as well as increase the holding strength Making this change would greatly increase the ratchet s performance As for additional capabilities of the robot the wireless capability of the CM 5 should be utilized Not only would the CM S be able to broadcast data during the experiment but the robot would not need to be attached during any part of the program Page 17 Additionally when the CM 5 is using the wireless module it would allow for external control by using a wireless controller This along with changes to the dynamic formula would allow the user to steer the robot for additional applications Page 18 Works Cited Hylands J 2008 June 27 AX 12 Page Retrieved April 15 2009 from TikiWiki http www bioloid info tiki tiki index php page AX 12 page Mehta V Brennan S amp Gandhi F 2008 Experimentally Verified Optimal Serpentine Gait and Hyperredundancy of a Rigid Link Snake Ro
6. stored Page 5 The CM 5 also has the capability to operate many servos at the same time Where the Arduino would need a custom power supply the CM 5 has two very large capacitors built into the board that are able to discharge enough current to run 28 servos simultaneously Robotis Co L Bioloid User s Guide 2007 These capacitors are charged by the 9 6V 2 3 Ah rechargeable battery with enough charge for more than an hour of testing Since the controller would have to both DIRECTION PORT 5V send commands and receive data from the servos it was important that the controller selected could both send and receive serial commands at a fast rate As the AX 12 unit operates both on a single i em CM 5 internal circuit HALF DUPLEX UART wire the controller needed to be able to do the Figure 4 Circuit diagram for CM 5 serial switch Robotis Co L same Both boards have a serial transmission Dynamixel AX 12 User Manual 2006 port Tx port and a serial receiving port Rx port but only the CM S had a hardware switch to rapidly switch one on and disable the other figure 4 The reason this is important is that a serial communication in both directions on the same wire could potentially cause a loop between the two ports and overload the board The Arduino does not have a hardware switch but can perform the switch slower via software programming Since the servos send a return packet of information immediately following
7. 0V 9 6V 7 0V 16 5kg cm 12 0kg cm 229 oz in 167 oz in 0 196sec 60 0 269sec 60 NB 360 Rotation Mode 1024 selectable speeds i e 10bit resolution Reduction Ratio Operating Angle Current max Operating Temp Size Weight Command Signal Protocol Link Number of modules Com Speed Position Feedback Temperature Feedback Load Voltage Feedback Input Voltage Feedback Compliance Driving Settings Material Motor 1 254 300 900mA 5 C 85 C 50 x 32 x 38 mm 55g Digital Packet Half Duplex Async Serial 8bit 1stop No parity TTL Tx amp Rx multiplexed on single core 254 valid addresses 0 to 253 7343bps 1Mbps Yes Yes Yes Yes Yes Engineering Plastic Gears and Body Cored Motor Figure 2 AX 12 Specifications Trossen Robotics Dynamixel AX Page 3 The final feature that made this servo the best choice for the project was the ability to daisy chain as many as needed together with only a single power source and master controller The servos are connected to each other by a 3 wire cable containing power ground and data The data is transmitted via half duplex asynchronous serial communication which is transmitted to and from the servos Each data packet contains a servo identification number as well as instructions which allows the control of all the servos connected on the same wire What this meant for the project is that there only had to be one con
8. THE PENNSYLVANIA STATE UNIVERSITY SCHREYER HONORS COLLEGE DEPARTMENT OF MECHANICAL AND NUCLEAR ENGINEERING DESIGN AND PROTOTYPING OF A ROBOTIC RESEARCH VEHICLE TO INVESTIGATE AND VERIFY THE CALCULATED EFFECT OF COMBINED LOCOMOTION AND SERPENTINE GAIT TREVOR J OWEN Spring 2009 A thesis submitted in partial fulfillment of the requirements for a baccalaureate degree in Mechanical Engineering with honors in Mechanical Engineering Reviewed and approved by the following Sean N Brennan Assistant Professor of Mechanical Engineering Thesis Supervisor Matthew M Mench Associate Professor of Mechanical Engineering Director Fuel Cell Dynamics and Diagnostics Laboratory Honors Adviser Signatures are on file in the Schreyer Honors College We approve the thesis of Trevor J Owen Date of Signature Sean N Brennan Assistant Professor of Mechanical Engineering Thesis Supervisor Matthew M Mench Associate Professor of Mechanical Engineering Director Fuel Cell Dynamics and Diagnostics Laboratory Honors Adviser 9 1311 7522 Abstract Throughout the last 20 years a lot of work has been done on the investigation into serpentine dynamics and developing mathematical models for motion However there has not been as much work testing the dynamic models with hardware The purpose of this thesis is to design and prototype a research vehicle to test various models of serpentine dynamics which include serpentine g
9. ait and powered wheel locomotion In designing the robot selecting the proper hardware was the foundation on which to build on For the links the AX 12 servo was chosen for its networkability to power both the link angle and wheels To control the entire robot the CM 5 controller module was superior to other options because of its programming library serial hardware switch extended memory and superior power source These components combined with a framing kit comprised the structure of the robot In accordance with the mathematical model the robot was designed with 6 links and 5 joints The programming was structured with a user interface to walk the user through the experiment including preset variables or user defined variables During the experiments the robot would not be tethered for the duration and then reconnected at the end for data collection There are many different modes of motion and feedback parameters included in the robot which make it very reconfigurable The robot was tested for operation and showed very promising serpentine motion and feedback operation It holds a number of advantages over the previous versions as well as huge potential for further experiments This robot allows for many different types of testing utilizing a serpentine gait and configurable powered wheels Table of Contents THEO AUC CIO ig srs ca deriv che Sood tcoeasaisanacta ie onei Rieni Page 1 Robot Hardware Selection cccccccccccsseeseeees
10. bot EEE Transactions On Robotics Vol 24 No 2 Mellis D A 2009 March 24 Arduino Duemilanove Retrieved April 15 2009 from Arduino http arduino cc en Main ArduinoBoardDuemilanove Robotis Co L 2007 Bioloid Expert Manual Bucheon city Gyeonggi do Republic of Korea Robotis Co LTD Robotis Co L 2007 Bioloid User s Guide Bucheon city Gyeonggi do Republic of Korea Robotis Co LTD Robotis Co L 2006 06 14 Dynamixel AX 12 User Manual Burcheon city Gyeonggi do Republic of Korea Robotis Corporation Trossen Robotics L 2009 Bioloid CM 5 Control Module Retrieved April 15 2009 from Trossen Robotics http www trossenrobotics com bioloid cm 5 control module aspx Trossen Robotics L 2009 Dynamixel AX 12 Robot Actuator Retrieved April 15 2009 from Trossen Robotics http www trossenrobotics com dynamixel ax 12 robot actuator aspx Page 19 Appendix materials tools and programs used Materials Used Part name Number required CM 5 Control Module 1 AX 12 Robot Actuator 17 17 Servo Cables 17 BPF F13 F14 Wheel and Tire Set 24 BPF WA BU Washer and Bushing set 17 BPF F2 Frame 5 BPF F10 Frame 11 BPF F3 Frame 31 M3 10 Bolt 17 M3 Nut 12 M2 6 Bolt 160 M2 Nut 140 M2 10 Bolt 48 M3 Washer 15mm OD 12 Tools Used Phillips screwdriver Cutting tool Milling Machine Cordless Drill Plastic Bonder Threadlocker Profess
11. e Page 12 for t 1 t lt trun for bID 1 bID lt 5 bID pos a sin w t bID 1 b 200 512 WriteWord bID P_GOAL_POSITION_L pos t tstep MiliSec 50 Figure 10 Code segment for calculating and commanding servo position In addition to the commands sent down the servo chain the CM 5 also reads any feedback parameter of the AX 12 The speed of communication is so high 1 MB sec that it does not affect the fluidity of motion This includes the load position voltage or speed of the servo The variable measured depends on the parameter being tested The CM S starts to read feedback information towards the end of the run for steady state conditions and stores the information in an array that is later uploaded to a PC This stored data is located in the volatile part of the robot s memory and is lost once the power is shut off Once the user has reconnected and downloaded the stored feedback data the experiment is concluded and the program reaches its end Page 13 Testing the Robot Program and Hardware In order to verify the operation of the robot and its feedback data it was tested under several different modes These modes were used to verify the robot s ability to gather data as well as test its physical abilities The first mode tested was a straight train mode to test wheel operation wheel feedback and joint hold In addition to a flat surface the train mode was tested on
12. e motion however and a 40 degree incline is not an easy feat for a robot However the wheel grip can be increased with weight and strength in the ratchets can be increased with more directional teeth Unfortunately ratchets of this type are expensive and were not within the scope of this project Serpentine mode test To test the serpentine motion of the robot it was first placed in unpowered wheel mode and the ratchet wheels were replaced with the free spinning wheels This mode was to test the motion of the serpentine gait as compared to the previous version Before the current robot had weighted joints to distribute the weight from the battery pack at the head the serpentine motion was present but the mid section slipped back and forth This Page 15 meant that the mid section was not contributing to the forward motion and the front and back sections were doing all the work However after weights were added to equalize the load the robot worked very well and equaled if not outperformed the previous version of the robot After the unpowered wheel testing the ratchet wheels were reassembled and the robot was put through the powered wheel serpentine test This test intended to see if all the components of the program could work simultaneously This included commanding the serpentine profile of the joints powering the wheels and receiving feedback from the joint servos During the test the robot ran as smoothly as it did with the u
13. ed wheels the wheels were simply screwed in at these 4 points However for the other three modes of motion it became more difficult Ratchets had to be Figure 5 AX 12 hub Trossen Robotics designed that could handle free spinning wheels as well as Dynamixel AX 12 Robot ratchet wheels Many different designs were attempted but Actuator 2009 the final design proved to easily accommodate all the modes of motion Ratchets are basically gears with directional teeth and are usually used for high stress or long life applications Unfortunately this means they are usually made out of metal and very expensive to make For the ratchets on the robot a cheaper solution had to be found Nylon gears are relatively inexpensive and are easily machined to fit a custom purpose and so they were used as the basis of the ratchet figure 6 The outward Figure 6 Wheel ratchet Page 9 pointing gear teeth are not ideal but for this application they are sufficient To prepare each gear for mounting they needed to have the hub machined off and 4 holes drilled to match the mounting on the servo Once this was accomplished a plastic bushing was bonded coaxially to the outer surface of the gear to provide a frictionless mount for the wheel In addition to the gear every ratchet needs a pawl which stops the gear from rotating backwards This part is usually a solid piece held down by a spring For this robot a springy piece of plastic anc
14. eees Page 2 The AX 12 Networkable Servo ceeeeeeeseeetees Page 2 The CM 5 Control Module ccc ccecceeeseeeeeeeeeeees Page 4 Robot Body Desionis ic ee ed ie dee Page 8 Cink Despi iia eare pease EE aE Sa Page 8 Wheel Deslier eren a a aiennaeiesse Page 9 Robot Program and User Interface Page 11 Testing the Robot Program and Hardware Page 14 Trami CS ia foe hase exctete ce etnote e o a RE TE Page 14 Serpentine T EStiwnavisaiterscssavidorsivssi neni wed e Page 15 Conclusions fiaiacescnsneinioln lee miimeolns Page 17 Recommendations cccecccccccssessescscssesseeescsseseeeeeees Page 17 Works Cited arerin ernn ieri in ENA E Page 18 Introduction The study of snake dynamics is a relatively new field Snake motion is fairly complex and is generally viewed as being an inefficient mode of travel In the last 20 years work has been done to calculate mathematical models and dynamics of snake motion and it is a common practice to model a snake s motion as a segmented body with a single axle and two wheels on each segment However these theories are seldom tested with actual hardware The purpose of this investigation is to create a research vehicle which can be used to test combinations of snake dynamics that include serpentine gait as well as powered wheel locomotion This project intends to build on the success of an earlier project by Vipul Mehta Mehta Brennan amp Gandhi 2008 which created a serpentine robot
15. escribing the motion of the first link and adds a phase lag for each additional link figure 9 The code written for Qi asin wth 2 1 3 the serpentine robot uses this sinusoidal Figure 9 Equation of snake motion Mehta Brennan amp Gandhi 2008 equation to calculate the goal position of each link to create a sinusoid profile and continuously sends an updated profile until a designated end time This creates the sinusoidal motion needed to propel the robot forward The sinusoidal motion is characterized by 4 variables amplitude frequency time step and phase lag As the time step and frequency both have an equal effect on the sinusoid the time step is fixed and the frequency is used to change the profile There are two things that make this motion of the robot counterintuitive First is that if the links are calculated from the first link back to the tail the time variable must be set as a negative value This allows the sinusoidal motion to move down the tail rather than up it Also the amplitude and frequency variables only control the sinusoidal motion of the first link not the entire profile The subsequent links are controlled by the phase lag variable which can be set low for a tighter sinusoid or high for a loose sinusoid The code structure is seen in figure 10 The centerline for the position of the servo is 512 of the total range of 1023 This means the sinusoidal wave needs to be converted to the specified rang
16. h of the robot This caused a problem with the weight distribution as the mathematical model calls for equal weight on each link and the CM 5 is a significant amount of weight to add to the first servo This caused the robot to arch in the middle slightly decreasing the frictional force on the middle links The solution to this was to weight the other links with scrap metal to evenly distribute the weight along the robot The robots form matches the mathematical model in shape and degrees of freedom To further separate the robot from the previous version this version had servos to power the wheels and explore a different set of dynamics However the robot also had to be backwards compatible to test free wheels as well As a result each wheel was designed for four different modes The wheels can be attached firmly to the servos Page 8 allowing for no slip to test high torque applications or be attached on bushings which allow for backwards compatible free wheel motion Also the wheels were given a set of ratchets This allowed for powered or unpowered wheels that could only move in one direction The new transformable wheels allow for many different modes of testing increasing the possibilities of research for the robot Wheel Design AX 12 Physical Dimensions The design of the wheels to allow for so many different modes was complicated Each servo spins a flat disc which has 4 attachment points on it figure 5 For firmly attach
17. hored on the wheel itself was used The plastic is held at a near tangential angle to the gear so that it locks when trying to move the wrong direction This completes the ratchet and covers the two ratcheted modes of motion In addition to this extra wheels are on hand to replace those with a pawl attached in order to have free spinning wheels Each type of wheel is held on the bushing with a washer and nut on the outside The robot is complete physically figure 7 It has the exact form to match the mathematical model and is reconfigurable to test different modes of motion The microcontroller and power source allow the robot to run independently and tether free for operational convenience The next step in finishing the design of this robot is to complete the software side and program the robot to accept multiple profiles of motion Figure 7 Completed serpentine robot Page 10 Robot Program and User Interface The robot is programmed with a certain intuitive program structure of setting up the experiment running the experiments and getting the feedback data During the set up and feedback portion of the program the robot outputs data and user interface information to the serial port on a laptop A sample user interface progression can be seen in figure 8 Most any serial communication program can be used but this robot was designed to work with Robot Terminal In the initial stages of the program the robot is programmed for the opti
18. incorporated in this robot the wireless capability of the CM 5 could be a useful addition for future robot variants Although both the PC and the Arduino were used in learning to control the servos the CM 5 was ultimately chosen to control the robot It incorporates so many features that were designed to communicate with the AX 12 servos that it became the obvious choice Open source compilers programming language and command libraries also make it easy to work with and also allow for users to visit online forums to troubleshoot hardware and software issues In addition to fulfilling the hardware and software requirements for the project the CM 5 also has a few untapped features such as the Page 7 wireless communication feature that make it a promising board for future versions of the robot For all these reasons the CM 5 was chosen as the controller for the serpentine robot Robot Body Design Link Design To accurately fit the mathematical model the serpentine robot was designed to have 6 links and 5 joints This allowed for a direct match to the model without having to consider extra links Each link is made up of 2 AX 12s driving the wheels and 1 AX 12 driving the link angle A considerable amount of framing holds the servos together and connects them to the following link Lastly each servo is wired in a daisy chain formation to the next At the head of the robot is attached the CM 5 unit which will send commands down the lengt
19. ional Epoxy Programs Used Bioloid libraries and Terminal Downloadable from www robotis com zbxe software_en WinAVR Downloadable from http winavr sourceforge net download html Page 20 Appendix 2 Serpentine Robot Code include libcM 5 h allows use of Bioloid Command Library include math h allows use of trig functions int main void initialize hardware PortiInitializeQ initializes Serial ports TimerInitializeC TIMERO 128 1 Interrupt Enable SerialInitializeC SERIAL_PORTO 1 RX_INTERRUPT 485 serial communication to Dynamixel Servos SerialInitialize SERIAL_PORT1 DEFAULT_BAUD_RATE RX_INTERRUPT 232 serial communication to PC ChargeIninterruptinitializeQ initialize ability to charge battery seiQ initialize interrupt defining variables int arraytotal arraypos byte bID bkey word pos jspeed wspeed cwspeed float a w b t trun tstep User defined values ooo d jspeed 100 wspeed 400 cwspeed wspeed 1024 must add 1024 for counter clockwise spin trun 30 tstep 0 5 user interface message to PC TxDStringC r n welcome to the Snake Robot Control Program r n MiliSec 1000 pause for 1 second LEDON BIT_LED_MANA turn on manage LED TxDString r n would you like to charge the battery Up yes Down no r n bkey WaitButtonChange wait for user to make button choice if bkey BIT_Sw_uP if user selects t
20. is special because each one houses a large amount of technology that incorporates all the projects goals into a compact package The servos each contain an ATMega8 amp Figure 1 AX 12 Trossen microcontroller Hylands 2008 which allows it to operate Robotics Dynamixel AX independently from the master controller The servo casing also contains feedback hardware and can report information and make decisions based on internal conditions The servos have high torque for a relatively low weight 16 5 kgf cm 55g Robotis Co L Bioloid User s Guide 2007 In addition each servo is modular and has several attachment points which can be used for snake construction making the servo itself into Page 2 the snake link The compact nature of these servos and their ability to do so much made them an obvious choice for the project Each servo has a multitude of functions that can be commanded from the controller The servo can provide feedback on position speed temperature load and input voltage and can be commanded by goal position speed torque compliance and operational limits The servo can make decisions based on this information without having to interrupt the master controller allowing for smoother operation The sheer amount of features compacted into the servos casing was very useful for this project AX 12 Actuator Specs Operating Voltage Holding Torque No load Speed Maximum Typical Minimum 10
21. ler as the Arduino but with some key hardware differences that make controlling the servos easier which will be explained later The enclosure for the board is a plastic housing with several buttons and LEDs which are connected to the board s inputs and outputs The housing also includes a serial port for wired communication to a PC and a 3 wire serial bus for communication to the servos In addition to the board the housing also incorporates a 9 6 V rechargeable battery and has multiple hardware attachment spots on the outer perimeter for attaching the servos One of the hardware advantages the CM 5 had over the Arduino was the massive amount of onboard memory The CM 5 has 128 KB of flash memory 4 KB of RAM and 4 KB of EEPROM Robotis Co L 2007 as compared to the Arduino s 16 KB of flash memory KB of RAM and 512 bytes of EEPROM Mellis 2009 Each type of memory is important for a different purpose The flash memory is where the board stores the program used to run it which includes the user interface the equations for calculation and the commands given to the servos The RAM is a volatile memory which is used to store variables created during the program and is wiped when the power is disconnected The EEPROM memory is used for a multitude of uses but in this case is used for serial communication and servo information storage With a greater amount of memory on the CM 5 more complex programs and longer strings of data are able to be
22. npowered wheel test although it was quite a bit louder with all 17 servos operating A portion of the feedback can be seen in figure 12 One thing that was noted about this mode is that the forward motion is dominated by the wheel speed variable and the serpentine gait seems to increase forward momentum only slightly However the test was a success as the feedback data proved that the robot could perform all operations at the same time Position deg Dynamixel ID Speed RPM ftom Center 1 11 6 29 6 2 9 8 15 2 3 10 3 2 05 4 3 6 19 4 5 11 7 30 5 1 8 5 29 9 2 9 8 21 1 3 9 8 2 6 4 9 36 14 4 5 11 7 31 1 Figure 12 Feedback data from serpentine test Page 16 Conclusions The final design for the robot turned out to be better than expected The speed of communication from the controller to the servos is so fast that the serpentine motion of the robot is fluid despite the additional strain of data acquisition In addition to the link hardware the ratcheting wheels turned out very well With the rolling friction minimized while still being able to prevent opposing motion the ratchets perform their job well Also the ability to operate the robot without a tether makes operation of the snake very convenient and the user interface drastically lowers the learning curve This robot fulfils all the requirements needed to test experimental motion as defined by the mathematical
23. o charge the battery gbBatteryChargeMode BATTERY_CHARGE_MODE_ING starts the battery charge TxDStringC r n Battery Charging Restart program when finished while 1 infinite loop to charge the battery LEDOff C BIT_LED_MANA turn off manage LED Mi1liSec 1000 LEDOn BIT_LED_PROG turn on program LED ao Select one of the following options Press directional button r n TXxDString r n UP Run winding serpentine program with powered wheels TxDString r n DOWN Run winding serpentine program with unpowered wheels TxDString r n LEFT Run straight train program presets TxDString r n RIGHT Use user defined values r n TxDStringC r n Choice bkey 0 while loop for incorrect button presses while bkey BIT_SW_UP amp amp bkey BIT_SW_DN amp amp bkey BIT_SW_RT amp amp bkey BIT_SW_LF bkey WaitButtonChange wait for user choice switch bkey switch to determine actions from user s choice case BIT_SW_UP TxDStringC UP clarifying choice a 0 8 redefining values Page 21 w 0 5 b 0 8 jspeed 100 wspeed 1023 cwspeed wspeed 1024 trun 100 tstep 0 5 break exits switch case BIT_SW_DN PepstringCIDONN l w 0 65 b 1s jspeed wspeed 1 cwspeed wspeed 1024 trun 100 tstep 0 5 break case BIT_SW_LF TxDStringC LEFT a 0 w 0 5 b lis jspeed wspeed 1023 cwspeed wspeed 1024
24. on of charging the battery This is a terminal branch of the program and if chosen will end the simulation to complete the charge over approximately 1 hour for an empty battery If charging the battery is not chosen the robot queries the user with a few options on what simulation to run There are three preprogrammed simulations as well as a custom option to enter user defined variables The three preprogrammed modes work with all 4 wheel modes and consist of a straight train mode a powered wheel serpentine mode and an unpowered wheel serpentine mode The forth mode asks the user for each variable individually The robot then instructs the user to disconnect the serial cable while it runs the program and then to reconnect the cable at the end to retrieve the data Welcome to the Snake Robot Control Program Would you like to charge the battery Up yes Down no Select one of the following options Press directional button Run winding serpentine program with powered wheels Run winding serpentine program with unpowered wheels Run straight train program presets RIGHT Use user defined values Choice UP Variables set remove serial cable and press START to begin progranm Figure 8 Sample user interface progression for powered wheels Page 11 The control formula for the motion of the serpentine robot is based on the work of Vipul Mehta in his paper on serpentine gait Mehta Brennan amp Gandhi 2008 It is sinusoidal in d
25. troller and power source located at the head of the robot and would free up a lot of wires required to run each servo individually The ability to control all the servos from a single local controller and power source gave the robot a huge advantage over the previous model The CM 5 Control Module Now that the servo choice has been made A proper controller had to be chosen operate the robot The controller needed to fulfill certain requirements Peteteteteteieters including running a user interface calculating the Figure 3 CM 5 Module Trossen positions of the servos serially commanding the RepoHes Bilin cM rental servos and reading information from the servos It Module 2009 also needed sufficient speed to compute all the operations in order to maintain smooth serpentine motion Additionally it needed to be small enough to be integrated into the robot or have a wireless capability Other qualities of the controller that were not required but beneficial were ease of programming open source code low cost and availability Page 4 From these criteria the choice was narrowed down to running a laptop based controller wirelessly an Arduino Duemilanove controller and a CM 5 controller figure 3 sold by Robotis These three met the requirements but ultimately the CM 5 was the best solution The CM S is an enclosed printed circuit board with an Atmel ATMegal28 microcontroller This board uses the same microcontrol
26. with free spinning wheels However there were several setbacks with this project that needed to be redesigned The robot operated while attached to a tether which it relied on for control and power This made it difficult to operate and inconvenient in many situations Additionally the general design although operable was cumbersome and fragile The joint between links was long and prone to bending The wheels were too big and heavy The components of the links were bulky and needed a multitude of wires strung between the joints The redesign of the robot targets most of these areas and adds the ability to power the robot s wheels Page 1 Robot Hardware Selection The AX 12 Networkable Servo The design for the robot depends on the foundation of properly selected servos Each link of the robot needed to have a servo to control the link angle two servos to power the wheels feedback hardware such as encoders and current meters as well as the ability to power and command the servos The previous version was made with all these components separately and with the servos controlled individually through pulse width modulation Each link had a wire tether which made for awkward operation For the current version new technology is available which simplifies all these operations The servos chosen for this version of the robot were AX 12s which are sold by Robotis under their Bioloid product line figure 1 figure 2 The design of the AX 12s
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