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Originally Posted by KenWittlief
it would be interesting to see what the curves look like with more load on the motors - I think the curves would be far more linear and straighten out.
Controllers usually put out a voltage signal, and that normally corresponds to torque out of the motor (not speed)
so the voltage to speed curve becomes a function of load:
Voltage => torque (into a load) => speed
with no load (or a small load) applied the motor speeds up much easier.
this might also flatten the curve at the upper and lower ends ( the top and bottom 15 levels of the PWM commnand).
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Good point you bring out about voltage being more closely related to torque than speed. And that is why I made the post because it would not do much good to linearize against bad data in the first place. I don't really know how to set up a dynamometer easily. I could fairly easily measure stall torque as a function of the PWM setting just in the non-linear region toward full voltage and see if it is flat or not for starters. My real goal here is to use vEx as a teaching platform for FRC and I want the students to consider if it might make sense to linearize the motor response so that a % PWM change from a PID output came closer to corresponding to the same % change in the wheel speed, for instance. And that it is a better approach to deal with the motor response at the "motor driver" level than to tweak the PID parameter tuning (as an example) to account for the general slope of the more or less linear region of the motor response. Although the loop parameters will end up being driven by the dynamics of the platform anyway and maybe it makes no practical difference if the motor response whatever it is is thrown in the mix. It is also an excuse to use the EEPROM for the table although we need SIN/COS for other purposes.
Thanks,
Greg