Duckcar1_Instruction

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Orange Coast College *

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A180

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Electrical Engineering

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Feb 20, 2024

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EGME 476A 1/ 3 Duck Car Lab 1: Open Loop System Characterization Objectives: • Obtain the mechanical time constant in open-loop. • Gain intuition for loop gain analysis 1 Pre-lab 1.1 Tracker Video Analysis and Modeling Tool Install the software from https://physlets.org/tracker/ and familiarize yourself with it. See the Tracker Video Tutorials section on that website. 1.2 Description of the lab and modeling As discussed in class, for many DC motors the time constant of the armature τ a = L/R is negligible and the motor can be modeled as a first order system. The idealized open-loop transfer function of the duck car between the car position x ( t ) and voltage into the motor is of the form G ( s ) = K m s ( τs + 1) where K m is a motor gain ( m/s V ) and τ is the time constant ( s ). In the “Open loop system characterization” part of the lab, you are changing the output from the power amplifier which supplies the voltage to the motor so the open loop transfer function for the system from input to the power amplifier to car position is G ( s ) = K a K m s ( τs + 1) where the amplifier gain K a = 1 . 2 V V (fixed) as seen in Figure 1 . Figure 1: Open loop model of the duck car where the model abstracts the disturbance due to friction as an effective voltage on the motor, W ( s ) . The DC gain of this system is K = K a K m and the time constant is τ . You are going to estimate the time constant and DC gain for each input voltage case you recorded during lab.

EGME 476A 2/ 3 2 Open loop system characterization Equipment: • digital video camera • duck car and potentiometer • voltmeter • tracker software • tape ruler Setup: Position the camera far away, aiming perpendicular to the linear motion of the cart; Have enough travel distance for the cart to reach steady-state speed (~8 m). Procedure: 1. Remove the output wire (blue wire) from the op-amp and connect it to the center pin of a potentiometer, with ends at ± 12 V . (This has already been done for you.) 2. With the motor switch off and the power on, adjust the potentiometer so the output of the amplifier reads 3 V . Figure 2: The output of the power amplifier on every duck car is the second from the bottom on the power bus. To find ground follow the black wire from the prototype board back to its location on the power distribution bus. 3. Place the car at the start point, start the recording, switch on the motor. Catch the cart at the end of travel, stop the recording. For the best recording, make sure to stand far enough away so that the start and finish are viewable without moving the camera. Also, make sure to have some known size object/ruler in frame so that you can set a scale for the video tracker software later. 4. Repeat steps 2 and 3 for 4 V and 5 V respectively.

EGME 476A 3/ 3 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. 3.1 Open Loop Characterization Analysis 1. Import the 3 videos into the tracker software and generate data tables. 2. Calculate and plot velocity vs time for each data set. 3. Determine the time constant of the exponential using two different methods and DC gain in each case. Deliverables • One plot of velocity vs time containing the data for all three input voltages • A table containing the time constant and DC gain information • A short description of the two methods used to obtain the time constant.

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