Pre-lab: Motor Control Circuits

The questions below are due on Friday November 01, 2024; 05:00:00 PM.

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Recall that in last week's lab, we were able to make a motor spin in both directions using a unipolar supply (last week it was 0V and +20V) by supplying our input voltage v_{\rm in} on one side of the motor, and a fixed offset voltage (created with a voltage divider and an op-amp) on the other side, like so:

What is the voltage drop across the motor in the circuit above? Enter a symbolic expression in terms of v_in and v_offset. Note that those variables are case-sensitive!

Drop across motor =

In this week's lab, we're going to be building a little mobile robot, so we won't be able to use the benchtop power supplies to provide power; instead, we'll be using a 9V battery. This smaller supply voltage means that using the circuit above, we would be able to get a swing of only (at most!) \pm4.5 Volts across the motor, which wouldn't be enough to make the robot go. As such, we'll be using a different circuit this week, which is related to one of last week's p-set problems and which will allow us to get bigger swings across the motor:

What is the voltage drop across the motor in the circuit above? In your analysis, make the ideal op-amp assumption, and ignore any limitations imposed on the op-amp's output by the power supply. Enter a symbolic expression in terms of v_in, v_offset, and/or R. Note that those variables are case-sensitive!

Drop across motor =

Make sure you're prepared to discuss your work for solving this circuit during lab on Friday. If you're having trouble with it, feel free to ask for help at the start of the lab; but definitely try your best.