Reverse spindle no pwm

motion.spindle-speed-out pin is negative when the spindle is reversed.

PWM type 1 sets the output to zero with negative input ( so the docs say )

Are you sure? thats true for mode 0 but the pwmgen manual says no such thing for mode 1

If PWMGEN does output 0 PWM in mode 1, then its serisouly broken and should be fixed(since mode 1 has a direction output and the only way to make direction high is a negative input)

sorry your right. I miss read.

this would be how to use abs to have pwm on reverse spindle rotation (negative speed out)


# load abs component
loadrt abs count=1
# add abs to thread
addf abs.0 servo-thread
# hijack the spindle speed out and send it to abs in
net speed-to-positive abs.0.in <= motion.spindle-speed-out
# send the always positive abs output to pwmgen
net spindle-speed-cmd <= abs.0.out => pwmgen.0.value

There actually is no direction signal available. There is a spindle cw and spindle ccw signal that could be used.
So should we add the direction signal and if it is selected then the PWM should be type 1 other wise type 0 ?
Or add a checkbox for positive PWM only? I think I favor the direction signal.
the only problem i see is it is not obvious how stepconf will pick what type of PWM ( unless we use the checkbox)

Chris M

I think what John means is if the user wants a reversable spindle, PWM mode1 should be used. In this case the PWMGEN works with positive and negative inputs and generates a direction output that can drive a physical output pin. For non reversable spindles, PWM mode 0 shoulld be used

well one can use the cw and ccw signals to select the direction.
What i mean is there needs to be a way to let stepconf know that the user wants a PWM signal that is always positive or positive and negative.
And it needs to be done in such a way that it is obvious to the user.

right now it seems it ignores negative PWM but does set the ccw signal.

There is a spindle cw and spindle ccw signal that could be used.
So should we add the direction signal and if it is selected then the PWM should be type 1 other wise type 0 ?
Or add a checkbox for positive PWM only? I think I favor the direction signal.

That makes sense to me.
It seems the most common combinations would be;
A spindle that only goes one direction.
A spindle that always uses a positive pwm signal and reverses with a signal pin, such as the VFD and Mesa combination I use.
A spindle that uses a positive and negative signal to select direction and speed.

Rick G