Electrical – Analyzing 24V fast PWM signal in Arduino

I would choose the more modular support, with that ATtinys running the motors, with the ATtiny you could add extra features like position, or encoder data, emegency start/stop and other features. As for the main control unit, the arduino may be under powered for fast work but it is possible.

you may want to also look at the Reprap project for more idea for hardware. another resource that may help is the emc2 supported hardware.

you would not be able to hook up emc2 right to the steppers with out have some sort control module.

It looks to me that your control loop is essentially:

if speed is too slow:
    increase PWM duty cycle one unit
if speed is too fast:
    descreate PWM duty cycle one unit

As you have observed, this doesn't work so well. Your control loop cyclically overshoots the target speed.

The canonical solution to this sort of problem is a PID controller. The concept is essentially the same, measure a thing and compare it to a target to calculate an error. Then adjust something (in your case, PWM duty cycle) based on the error.

However, a PID controller has three error terms:

• P: the current error
• I: the integral of the error
• D: the derivative of the error

For each of these terms, the controller has programmed some gain. It then multiplies each term by the respective gain to calculate how much the control input (PWM duty cycle) should be changed. Properly tuned, this allows you to get a feedback loop that at first ramps up the duty cycle, then as your vehicle approaches the target speed, backs off smoothly so you get a minimum of overshoot.