High frequency Stepper Motor driving

Mickster · 2023-07-16 10:34

How would we handle this on the P2, is there a smartpin mode that would suit?

Craig

iseries · 2023-07-16 11:26

Not totally following you here. The DMC controller is able to control X number of servos or stepper motors up to 6 million steps per second.

The P2 can output pulses at that rate but needs a driver board to handle the motors.

A smartpin would really not be needed here as you want to control these motors by outputting a number of pulses at a set or scaled frequency to do precise movements.

There is a smartpin mode to control servos that are driven by a frequency though.

Mike

Mickster · 2023-07-16 11:49

@iseries said:
Not totally following you here. The DMC controller is able to control X number of servos or stepper motors up to 6 million steps per second.

The P2 can output pulses at that rate but needs a driver board to handle the motors.

Oh, this is understood. I am only interested in generating the pulse/direction signals.

A smartpin would really not be needed here as you want to control these motors by outputting a number of pulses at a set or scaled frequency to do precise movements.

I have never driven a stepper because I am more of a closed-loop servo guy and so my initial thoughts are:

I already have the velocity profiler/trajectory generator which runs @500Hz, the output of which feeds the PID and the PID is responsible for commanding the BLM or whatever. For a stepper, I imagine dumping X number stepper pulses in a register and specifying the rate at which they are sent to the stepper driver. Or am I overcomplicating this?

Craig

Simonius · 2023-07-16 13:49

%00100 = pulse/cycle output
this smartpin mode should work

output N pulses at X frequency and then stop

if your control loop runs at 500 Hz, you have a 2 milliseconds frame that each of the axe's smart pins should fill with steps. it is unlikely that it fills this 2 ms frame exactly, it will always have to wait a little. this will lead to jittering if not cared for.

Mickster · 2023-07-16 14:22

@Simonius said:
%00100 = pulse/cycle output
this smartpin mode should work

output N pulses at X frequency and then stop

if your control loop runs at 500 Hz, you have a 2 milliseconds frame that each of the axe's smart pins should fill with steps. it is unlikely that it fills this 2 ms frame exactly, it will always have to wait a little. this will lead to jittering if not cared for.

Excellent! Many thanks and yes, I expect that some form of buffering might be required. If the smartpin can be used, I'll make it work.

P2: The answer is "yes", now, what's the question?

Craig

pik33 · 2023-07-16 17:36

I control a stepper in my robot. It extends or hides the arm with lamps. No advanced stuff there at all As it does its job at needed speed, I didn't even try to play with smartpins or asm. Waitus() amount was determined experimentally to make the arm open at desired speed.

sub opendownarm

var q=0
var q2=0
q=pinread(end_a2)
if q=0 then exit sub
pinl(dir2)
do
  if block<>0 then exit loop
  q=pinread(end_a2)
  if q=0 then q2=q2+1
  if q=1 then q2=0
  if q2>=10 then exit loop
  pinl(pwm2)
  waitus(200)
  pinh(pwm2)
  waitus(200)
  if channel(l_button)<1800 then exit loop
loop 

end sub

JonnyMac · 2023-07-16 17:50

If you do want to try the smart pin route, it's pretty easy.

This sets up a pin to output pulses.

pub config_pulse_pin(pin, khz) | m, x

  m := P_PULSE | P_OE
  x.word[0] := 2 #> (clkfreq / (khz * 1_000)) <# $FFFF          ' ticks in period
  x.word[1] := x.word[0] >> 1                                   ' ticks in low cycle (50%)
  pinstart(pin, m, x, 0)

To generate pulses on a smart pin (with option to wait for conclusion of pulses).

pub pulses_out(pin, count, hold)

  pinfloat(pin)                                                 ' reset
  wypin(pin, count)                                             ' set new count
  pinlow(pin)                                                   ' start pulses

  if (hold)
    repeat until pinr(pin)                                      ' let pulses finish

Mickster · 2023-07-16 18:17

The only positive experience I ever had with steppers is that they put me in business
A huge machine destined for General motors had 3 huge stepper motor axes. Positioning was all over the place.

I was called in to investigate and told them that they needed to throw away this open loop garbage and stick some closed-loop servos on there. They hired me to make it happen and gave me carte blanche.

It was a success and they decided that they wanted a bunch more of these machines, provided that I developed the controls. Instant profitable business

I will never accept an open loop solution, no matter what

Craig

Mickster · 2023-07-16 18:38

@JonnyMac

Many thanks Jon...heck, the Props never fail to put a smile on my face

Craig

High frequency Stepper Motor driving

Comments