Interesting motor experiment

Our team plans to use PID in the future with our drive to make a very predictable autonomous program. We decided to make a program that would test the relation between the motor speed we set (127 to -127), and the RPM the motor actually reaches. We used an IME on a torque geared motor, and made a program that iterated through the motor speeds at an interval of 5 (so it tested speeds -125 to 125). The motor was set to a speed, and it’s RPM was recorded every 25ms with 200 repetitions, then it would go to the next speed. The results we found were pretty interesting, so I thought I’d post them so you could check them out:

(And here are the associated spreadsheets)

Note: The drop in the middle is where we switch from testing positive speeds to testing negative speeds. There was a long delay to make sure it was tested from a complete stop.

If you have any questions about how the data was generated, feel free to ask.

Yep, the weird relationship between motor command and speed can be a pain for both driving with the joysticks and any kind of PID autonomous programming. A good way of dealing this is to create a lookup table of motor control values that will produce a near-linear relationship like 24C did back in Sack Attack.

According to IME readings, 2 motors on 2 different circuits run at different RPM under 0 load.

I love VEX motors…

You will have better results if you use 2 brand new motors.

Will have to try that