Final Project Report Mechanical Engineering 224 Professor -PDF Free Download

FINAL PROJECT REPORT Mechanical Engineering 224 Professor
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Table of Contents,I Introduction,II Boe Bot Assembly. III Servo Calibration,IV Gyroscope Calibration,V Analog to Digital Converter. VI Programming and Debugging,VII Results and Conclusions. VIII Improvements and Future Considerations,IX Appendix A Servo Calibration Program. X Appendix B LabView Program for Gyroscope Calibration. XI Appendix C Turn Test Program,XII Appendix D Final Path Program.
2, I Introduction, The objective of this project is to use our knowledge acquired in Mechanical Engineering. 224 to control a Boe Bot along a specified path , Figure 1 Robot Path. using gyroscope sensing in a closed loop feedback system see figure 1 The Boe Bot robot is. mainly composed of two servo motors to operate the wheels and a Board of Education carrier. board which is controlled by a program called BASIC Stamp Specifically we will create a. BASIC Stamp program that will use a specified voltage which corresponds to a certain angular. velocity to control the direction of travel of the Boe Bot Then using closed loop feedback from. a gyroscope and ADC Analog to Digital Converter the Boe Bot will correct itself to travel in a. completely straight line , 3, II Boe Bot Assembly, Figure 2 Boe Bot. Our Boe Bot was brand new therefore unassembled First we attached the four. standoffs to the four corners of the chassis The standoffs support the Board of Education from. which the Boe Bot runs After centering the Parallax Continuous Rotation servos we attached. the servos to the chassis using Philips screws and nuts We then attached our power source the. battery pack to the underside of the chassis After that we attached the tail wheel ball and high. quality rubber band tires Lastly we connected the Board of Education onto the four standoffs . with the breadboard closest to the drive wheels And the Boe Bot was born See figure 2 for a. photo of an assembled Boe Bot , 4, III Servo Calibration. Figure 3 Boe Bot Servo, Before assembling the Boe Bot we had to calibrate the servo motors see figure 3 We.
used a program see Appendix A that sends the servos a signal telling them to stay still . Because the servos are not pre adjusted at the manufacturing facility from which they came they. will actually start spinning We then had to use a screwdriver and adjust the servos until they. were still This calibration is called centering the servos When the program input is PULSOUT. 12 750 it is centering the right designated by 12 servo to stay still 750 designates no. movement in either direction When the program input is PULSOUT 13 750 it is centering the. left designated by 13 servo to stay still When the input 750 is increased the servo will travel in. one direction and when it is decreased the servo will travel in the opposite direction . 5, IV Gyroscope Calibration, The main programming softwares we used in this project were LabView and BASIC. Stamp While we were capable of programming the Boe Bot to travel in straight lines and make. various turns with BASIC Stamp we did not know the actual angles the Boe Bot turned during. its test trials In order to be more accurate with our Boe Bot following its respective path we. integrated the response of a gyroscope in a closed feedback loop which will allow us to program. the robot to make turns at specified angles and will adjust the Boe Bot so it does not deviate from. its straight path , In this project we used an ADXRSS150EB gyroscope from Analog Devices It operates. on a 5 Volt power supply and is capable of sensing up to 150 degrees in angular motion This. gyroscope contains two polysilicon sensing structures which have capacitive pickoff structures. that are capable of detecting motion caused by a Coriolis force This Coriolis force is produced. when the Boe Bot rotates After the Boe Bot rotates the Coriolis force causes the two. polysilicon sensing structures to be displaced orthogonal to the vibrating motion of the Boe Bot . The capacitive pickoff structures on the polysilicon sensors then pick up the Coriolis motion and. a rate signal output is produced This rate signal is the feedback we need in order to ensure that. our Boe Bot turns at specified angles and follows a straight path . Before we wrote our final program we needed to calibrate the gyroscope and determine. the relationship between its angular velocities and their respective output signals We first. created a LabView program see Appendix B that plotted our gyroscope output signals versus. time , 6, Voltage vs Time, 5, 4 5, 4, 3 5, 3, Voltage V . 2 5, 2, 1 5, 1, 0 5, 0, 0 5 10 15 20 25 30, Time s . Figure 4 Gyroscope Response, This allowed us to see how the gyroscope output signals varied as the Boe Bot spun in a.
clockwise from t 5 s to t 17 s and then counterclockwise t 17 s to t 26 s motion see. figure 4 , The next step was to determine the relationship between the gyroscope s angular. velocities and their respective output signals In order to find this relationship we created a. BASIC Stamp program see Appendix C that spun the Boe Bot at various angular velocities . After each run we recorded the number of rotations and the respective times for each run the. Boe Bot completed This enabled find a relationship between the gyroscopes output signals and. their respective angular velocities See figure 5 , 7. Angular Velocity vs Voltage, 4, 3, y 1 3361x 3 0312. 2, R2 0 9999,Angular Velocity rad s , 1, Test Data. 0, Linear Test Data , 0 1 2 3 4 5, 1, 2, 3, 4, Voltage V .
Figure 5 Gyroscope Calibration Curve, 8, V Analog to Digital Converter. After mounting and calibrating the gyroscope we encountered a major problem The. gyroscope was outputting a voltage in the range of about 0 2V to 4 6V We needed to incorporate. the full scope of these values in our control of the Boe Bot However the pins on the Board of. Education of the Boe Bot can only read high or low To rectify this problem we decided to look. into ADC s which could then provide us with a range of values instead of just 1 or 0 After. researching various options online we decided to use the TLC0820AIN produced by Texas. Instruments Specification sheet can be found at http www s ti com sc ds tlc0820a pdf . The converter is an 8 bit analog to digital converter that uses the output of the gyroscope. RATEOUT as its input and then writes the values to pins zero through seven on the Boe Bot . Thus we could theoretically acquire a range of values from 0 to 255 instead of the original 0 or. 1 The converter uses the 5V power of the Boe Bot as its VCC which is the desired value on the. specification sheet thereby eliminating the need for an op amp circuit to power the converter . When wiring the converter onto the Board of Education we encountered another problem . namely a shortage of possible connections The Board only has 17 rows of pins but the converter. and the gyroscope each need 10 rows To solve this problem we purchased another small. breadboard from RadioShack and mounted it to the cart of the Boe Bot beneath the original. circuitry See figures 6 and 7 , Before starting to write a comprehensive BASIC Stamp program for the robot s route we. needed to determine if the converter was working as expected and was compatible with the Board. of Education To do this we used a variable voltage generator as the input and BASIC Stamp to. read in the values from the pins of the Boe Bot Since the maximum voltage the converter could. handle was 5V and the maximum output of the gyroscope was around 4 6V we found that it. worked nicely We varied the voltage generator from zero to 4 9V and found that the converter. 9, was wired correctly and working as expected We were now ready to incorporate the gyroscope. as the input and control the Boe Bot with BASIC Stamp . Figure 6 Robot with both breadboards Figure 7 ADC Installed. 10, VI Programming and Debugging, Because we chose to use only the BASIC Stamp programming language to control our. robot we developed a single program encompassing both the feedback and control of the robot . Development of this program required the integration of the information obtained in the. gyroscope and ADC calibration phases with the programs we had created to perform basic robot. maneuvers The calibration we achieved of the gyroscope produced a correlation between. angular velocity of the robot and the voltage generated by the gyroscope The output of the. gyroscope is the input to the ADC which produces an 8 bit binary number that the Board of. Education can read Testing of the ADC gave us a correlation between the digital numbers. produced by the ADC and the analog voltages that create them . Figure 8 The team at work, The program reads the output of the ADC and converts the binary signal to an integer.
value and then converts this integer to the corresponding voltage of the gyroscope output Using. the gyroscope calibration equation this voltage is then converted to an angular velocity . 11, Knowing the angular velocity of the robot and the sampling time a simple integration can be. performed by summing the product of the angular velocity and the time step to produce the total. angular displacement of the robot The program written performs these tasks and instructs the. robot to turn until the proper displacement has been reached regardless of surface conditions or. the time required to do so The initial runs were far from ideal but with iteration we were able to. produce a program that causes the robot to describe a parallelogram path with 45 and 135 . angles and equal length sides , In order to debug the program we tested the small programs that performed portions of. the route traveling straight turning 45 etc individually before integrating them into the final. program as subroutines The proper turn durations were achieved by iteratively modifying the. calibration in the calculation routine Straight line performance was established by first creating a. baseline servo setting that produced the straightest possible path without feedback then running a. feedback loop to correct the path if the robot deviated from straight ahead if the gyroscope. detected an angular velocity Figure 8 shows the team hard at work . The robot s performance is not as consistent as it could be nor are the measurements as. precise as we would like due to BASIC Stamp s inability to handle decimal numbers See. figure 9 for a sample of the testing procedure This introduced error as any decimal value is. truncated to leave only the integer This is particularly important during division operations . when any remainder is discarded Because BASIC Stamp can only handle numbers up to 65535 . the scale of numbers becomes an issue it is difficult to maintain accuracy when dealing with. numbers of varying magnitudes An additional problem is that there is a finite non zero time. step for the summing operation Ideally as the time step goes to zero the sum becomes an. integral but the Board of Education and the BASIC Stamp software require a finite amount of. time to run the program each time it loops These errors multiply over the integration to create. less accurate results The sensitivity of the instruments was another concern After processing. the gyroscope s output with the aforementioned BASIC Stamp mathematical complications the. 12, robot s closed loop straight line feedback is not robust enough to detect small path deviations . only large scale errors This could be corrected with more sensitive components faster. processing more precise computations or a combination thereof . Figure 9 The robot during testing for path accuracy. 13, VII Results and Conclusions, Our project was successful The Boe Bot follows the specified route successfully most of. the time It races smoothly along as it takes into account the feedback it receives from the. gyroscope Although this fulfills the basic requirements of the project there are many problems. with our current system that detract from the accuracy and consistency of our Boe Bot operation . First there are multiple problems with the BASIC Stamp program The largest problem is that. BASIC Stamp does not allow the use of decimal points This means that the numbers we use. must be scaled up and then subsequently scaled back down as we make our calculations that. determine the Boe Bot s route This scaling results in a large loss of precision Also variables. can only be declared to about 60 000 which makes it difficult to scale numbers to a large enough. number to prevent important values from being truncated Secondly there are problems with our. ADC While it converts the analog input from the gyro into a digital signal it has a number of. sensitivity issues In its current configuration the ADC can t detect small changes in angle This. allows BASIC Stamp to control the Boe Bot to some degree but it often produces inaccurate and. inconsistent results Ultimately the Boe Bot works however there are many improvements that. could be implemented , 14, VIII Improvements and Future Considerations.
As mentioned above there are numerous improvements that could be employed to. improve the Boe Bot s operation Figure 10 shows the robot during testing The most. important improvement involves making the ADC more sensitive This can be done in various. ways The most logical way is amplifying the signal with an operational amplifier There is a. detriment to this method however Amplifying the signal would improve the sensitivity but it. would also reduce the range of values that would be recognized The Boe Bot would. subsequently have to be operated at lower voltages to ensure that it didn t go out of the narrowed. range In addition the method of scaling number in BASIC Stamp to account for the lack of. decimal points could be refined There are other methods that produce higher precision but the. process is more tedious For our calculations the more simple method was used Finally all of. the equations and calculations would benefit from being recalibrated Many hours were spent in. the lab tweaking numbers and all of the tweaking resulted in better control of the Boe Bot With. more time there could be a larger amount of time dedicated to calibrating the Boe Bot and. refining numbers We had a limited amount of time for the project and the equations were. refined to be as accurate and consistent as possible. Figure 10 The robot connected to the computer during testing.

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