Picoborg Reverse stepper control trouble

It sounds like the code might be trying to drive the steppers a little bit too fast.

With both the updated library and the faster 3B+ it is possible the delay is not quite long enough now and the PicoBorg Reverse is trying to make steps before the previous one has finished. This will result in missed steps and can make some unpleasant sounds :(

The good news is that if it is the case the fix is simple, all you need to do is increase the step delays slightly. If you code is based on our pbrStepper.py example you will have this line towards the top of the script:

stepDelay = 0.002       # Delay between steps

All you need to do is increase the number and see if the steppers start working properly.

I would suggest you start by making the number much larger to see if it will help, say 5-10 times larger. If that does not change anything it might be a different problem. If it works you can keep trying smaller values until you start seeing problems, then stick with the smallest value which worked correctly.

It would seem unlikely that both boards have such a specific fault, but I am not certain what the problem actually is.

One thought is that if the board thinks it might have seen a problem (voltage too low, current too large, et cetera) it shuts the output off until the PWM cycles. At full power the PWM does not cycle so it stays off until the power setting changes.

If your script is based on the pbrStepper.py example there will be a line like this:

sequence = [[1.0, 1.0], [1.0, -1.0], [-1.0, -1.0], [-1.0, 1.0]] # Order for stepping 

try turning the output down a bit and see if the behaviour changes. For example this will run at 80%:

sequence = [[0.8, 0.8], [0.8, -0.8], [-0.8, -0.8], [-0.8, 0.8]] # Order for stepping 

Generally speaking steppers do not like being sat at full power too long anyway, you may find it actually behaves better at lower values.

I think we will probably need a bit more information to help resolve this properly. Can you answer the following questions for us:

1. Does either PicoBorg Reverse make any sharp noises when trying to run the steppers?
2. Are the steppers getting very hot when powered?
3. Do you have the specifications for the motors?
4. Have you altered the stepping sequence in your script?
5. Can you take some photos of the wiring between the two reverses and the motors?

The microstepping example in that post sacrifices some torque to keep things simple, which may explain the steppers struggling to move.

Try using this sequence instead of the microstepping loop:

sequence = [[+powerMax, +powerMax],
		    [+powerMax, -powerMax],
			[-powerMax, -powerMax],
			[-powerMax, +powerMax]]

On a different note, the page with the specifications you linked is for a whole set of steppers. Can you tell us the product code and if it is a 6 or 4 wire stepper.

I think there is a bit of confusion here about how the motor connections work.

M1+ and M1- are a pair, it is the difference in voltage between them which powers the motor / stepper coil. M2+ and M2- are a pair in the same way. Because of this you need to measure the voltage difference between + and -, not just the voltage on a single connection.

I think the best thing would be to take a step back and just try the standard stepping (not micro stepping) first to see if it works as suggested above.