[RéSOLU] Steppermotor moves erratically when DMX value is ramped up slowly

[Micropuller]

Whilst testing the steppermotor function, I noticed something strange.
When I change the DMX value quickly, the motor moves fine.
But when I ramp it up slowly, the motor behaves eratically, going back and forth.
It looks like the problem only occurs when I ramp up (from 0 to 255) and not when I ramp down (from 255 to 0).
Any idea what could be the cause of this?

https://youtu.be/0EKgoE_yOxc

[Jacques]

This back and forth is not at all normal!
I must admit that the dynamic speed management is not perfect, there are somes steps. This is the next project I plan to take care of.
But even with the current imperfections you shouldn't have these problems... Can you make a screenshot of your configuration please?

[Micropuller]

Hi Jacques,

I don't see how I can add a picture, so here are my setting for motor 1 (or 0):
Mode: stepper
Stepper to config: 0
Active: yes
Steps per revolution: 400
Revolutions per minute min/max: 100/2400 (I have speed set at DMX value 150, so about 58%)
Number of revolutions: 13,5 (There's a 1:27 reduction on the motor and I wanted it to do 0,5 turns)
Uninverted
Action: perform
Input: 8 bits

I'm using an external stepperdriver set at 1,36A RMS and 400 pulses/revolution

[Micropuller]

The strange thing is that it only does it when the DMX value is increased, not when it is decreased,

[Jacques]

Indeed it is very strange...
I'll try to reproduce your setting tomrow at home. i said I ll try because I am not sure if I'll get enouth time because of my family life !
There may be a resonance problem (look on the net for articles about stepper resonance). To find out, try another range of speed values (for example 10/400) to see if the problem is still there.

[Micropuller]

I tried several ranges. 1-100 (when I use 1, the stepper will barely move, unless I set the speed at maximum), 10-100, 25-500, 50-500, 100-1000 etc. It does the same thing on every setting.
I now have it at 50-550, that seems to be a combination where I can actually set the speed at maximum (255), without the motor stalling when I ramp it up as fast as I can.

[Jacques]

I understand, the interface is in French...
When you write an answer, at the bottom, you can click on "fichiers joints" to find your file.
Then, you have a button "insrer dans le message" so that the image is inserted in your message.

[Micropuller]

Ah, I see. Thanks!
I did have the forum translated to English, but missed the attachments-tab.

Schermopname (80).jpg (78.83 Kio) Vu 2493 fois

[Micropuller]

Maybe this will be of help when fault finding: I just tried to invert the steppermotor. It seems the problem is gone when I do that.

[Jacques]

What do you mean by "invert the stepper motor" ?