DuckCar_Lab2_Instruction

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Orange Coast College *

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A180

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Mechanical Engineering

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Feb 20, 2024

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EGME 476A 1/ 3 Duck Car Lab 2: Open Loop System Characterization Objectives: Understand the motivation and need for linearization Consider idealized system versus reality 1 Pre-lab 1.1 Background on Operational Amplifiers See notes from Lecture Week 6 2 Sensor Linearization In this lab, you will be looking at the entire duck car system in feedback, as seen in Figure 1 . Figure 1: Block diagram description of the entire closed loop duck car system. Initially, you will look at just the sensor dynamics. The infrared sensor provides a voltage V s = k x + a where x is the distance to the target in front of the sensor. You will record the voltage corresponding to different stand off distances, which allows you to linearize the sensor dynamics about a particular set point. The linearized sensor function takes the form V s = V s o + K s ( x - x o ) where K s is the sensor gain (which becomes the “block” in the block diagram representing the sensor), and V s o is the reference input corresponding to the desired set point x o . In the second part of that lab, you will observe the closed loop step response (while holding a proportional control gain from the op amp circuit fixed) for different set points. Equipment: digital video camera (optional) duck car and potentiometer voltmeter tape ruler resistors Procedure: Note: You can video record any of the behavior, so that you can reference it later! 1. Make sure the power and motor switches are off.
EGME 476A 2/ 3 2. Turn the system voltage on and ensure that the motor is switched off. 3. Place a white card 3 inches from the baseplate and record the sensor voltage for a standoff distance of 3 in. Repeat the measurement for standoff distances from 4 to 11 inches, taking a measurement each half inch. Record the measurements and create a plot. 4. Tune the summing junction potentiometer so that its voltage (the reference input into the summing junction) matches the value for a standoff of 5 in. Figure 2: The prototyping board with the summing junction trim 5. Remove the output wire (blue wire) from potentiometer used for the open loop characterization and connect it to the output of the op-amp. Set the op-amp gain, R 2 R 1 , to 1 by selecting the appropriate feedback resistors. (Both resistors initially are R 1 = R 2 = 10 k Ω ) 6. Place the white card 5 in. away from the sensor. Turn the car on to verify that it does not move. 7. Place the second white card 15 in. away from the sensor. Quickly lift the first card, exposing the further card, and observe the behavior. Record your observations. 8. Change the set point potentiometer so it has an output voltage corresponding to a standoff of 10 inches. 9. Place the white card 10 in. away from the sensor. Turn the car on to verify that it does not move. 10. Place the second white card 20 in. away from the sensor. Quickly lift the first card and observe the behavior. Record your observations. 11. Increase the op amp gain to 2, 3.3, and 4.7 by changing the feedback resistance and observe the performance for each gain setting with the 10 in. set point. Record your observations. 12. Determine the best gain that balances performance and “aggressiveness” (overshoot) and set the gain to that value. 13. Tune the potentiometer to set the standoff distance back to 5 inches. 14. Observe the performance at this set point with the new gain and record your observations. 3 Analysis and Deliverables Group submission: Each lab group needs to submit the deliverables below by Friday October 6 at 5pm. All plots and tables are to be presented formally and all writing should be aimed at an audience of peer engineers.
EGME 476A 3/ 3 3.1 Sensor Linearization Deliverables Answer the following: Based on your measurements of the sensor voltage at different distances, approximate the sensor gain ( V/in ) at a set point of 5” and at a set point of 10”. In your own words, explain why the duck car behaved differently at the 5” and 10” set points for a given controller gain. Is the duck car more likely to hit a new barrier exposed at a far distance when the controller is set to a close distance or a far distance? Speculate on why.
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