Avoid using timer0 or timer1 for pwm

[blurfl]

This builds on PR #385. Timer0 is used for Arduino internal timing, timer1 is used by the TimerOne library for the encoder and PID portions of the firmware. By avoiding those we can alter the PWM frequencies and maybe improve performance. Further, create a function to set the PWM frequencies of timers 2-4. Don't change it yet, different frequencies will require some PID tuning.

[BarbourSmith]

Awesome!! 👍 👍 ❤️

I read somewhere a while ago that we should really be using ultrasonic PWM frequencies for motors of our size

[blurfl]

I've played with 4096kHz, it wants some PID tuning.

[krkeegan]

First a caveat, I know very little about any of this.

I could be wrong, but if it needs a change in the PID tuning, something else may be going on. The only way I can see this causing this is if at 4000kHz the "voltage" produced by the PWM signal starts to drift in someway higher or lower than expected or the timers in the arduino start to drift see:

https://playground.arduino.cc/Main/TimerPWMCheatsheet

[krkeegan]

Also, is that a typo do we mean 4096Hz not kHz.

[blurfl]

You're right about the frequency, ~4000Hz is the step above 490Hz, and ~31000Hz is the step above that. I was looking at the slight lag of the red reticule behind the black one, but comparing to 490Hz it looks the same. The motors sure purr at 31000Hz!

I just found that the settings for timer2 are different from timers3,4. Timer2 does 989Hz with divisor 3 while the other two do 490Hz with that divisor. I wonder whether setPWMPrescalers() needs to special-case that? The higher frequencies (4000Hz and 31000Hz) use the same divisor o all three timers.

Timer2 frequencies Setting Divisor Frequency 0x01 1 31372.55 0x02 8 3921.16 0x03 32 980.39 0x04 64 490.20 <--DEFAULT 0x05 128 245.10 0x06 256 122.55 0x07 1024 30.64

[BarbourSmith]

This is so cool!!! 👍 👍 👍 👍