PID question

[lukevanoort]

I don't think it is realistically possible to choose constants that keep the output between 0 and 254. As for the division thing, it lets you get decimal precision without making the uC do floating point operations, which it is very bad at. (ex 34/100 is the same as .34, but the robot executes it much faster)

To find gains, we just make the setpoint something near the middle of the mechanism's travel (to keep oscillations from damaging the mechanism). Then we link the P, I, and D constants to an analog input on the OI. After that we twiddle the knobs in this order: increase P until it gets near the setpoint, increase I until it reaches the setpoint, and finish by increasing D until any oscillations present are damped. We then use the numbers determined this way as our constants. It actually takes very little time to do it this way, I think it took us maybe 20 minutes to tune three loops last year.