Lab 2 — Motor Characterization & Encoders¶
Practical focus¶
Measure actual wheel speed; encoder counts (if the hardware allows); RPM; test several PWM values; compare left and right sides; identify the dead zone and saturation.
Encoders are conditional
The lab plan marks encoder counting as "if we can do it". TODO — instructor: confirm whether the chassis has encoders before the session, and write the fallback path (timed revolutions by hand, marked wheel) either way. Students need a speed number regardless of which method produces it.
Objectives¶
- Measure actual wheel speed rather than assuming it from the PWM command.
- Build a PWM-vs-speed curve for each side of the vehicle.
- Identify the dead zone — the PWM below which the wheels do not turn at all.
- Identify saturation — the PWM above which speed stops increasing.
- Quantify the left/right mismatch you observed in Lab 1.
Procedure outline¶
TODO — expand into numbered steps.
- Set up a repeatable speed measurement (encoder counts, or timed revolutions of a marked wheel).
- Sweep PWM across the usable range. Suggested points: 0, 60, 100, 130, 160, 190, 220, 255.
- Record speed for each side separately, with the car lifted.
- Plot both curves on one graph.
- Read the dead zone and saturation point off the curves.
| PWM | Left speed | Right speed | Difference |
|---|---|---|---|
| 0 | |||
| 60 | |||
| 100 | |||
| 130 | |||
| 160 | |||
| 190 | |||
| 220 | |||
| 255 |
Deliverable¶
PWM–speed curves + left/right motor characterization.
Carry this into Lab 6
You now know the two sides differ, and by how much. Could you cancel the drift by simply offsetting one side's PWM by the difference you measured? Try it. Note carefully where it works and where it stops working — that gap is the argument for feedback control.