Hello! I'm building an SLA printer and currently figuring out the electronics.

3D Printing
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Hello! I’m building an SLA printer and currently figuring out the electronics. My plan is to use RPi 3 with nanoDLP software which sends gcode commands to Arduino Mega running Marlin. I have Trinamic TMC 2130 driver for one 0.9deg stepper and I’m having problem shown in the video.

The problem is weird “floating” with the stepper motor after it have done the movent it should do. This problem occurs only when I’m using RPi 3 with nanoDLP, not when running Arduino connected to PC. I’ve tried two different USB cords (both are 1.8m long though), and it didn’t make a difference. Also lowering the acceleration makes it only worse.

Do any of you have an idea which could lead to this kind of behavior on stepper motor?

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Don’t drop the ENABLE signal after the movement. Keep that high to keep the motor locked to the last position.

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@Jason_McMullan ​ Driver and motor stays enabled after the movement so that is not the case. Thanks for your input!

This behaviour happens only when using RPi 3 as g code sender. I believe the problem lies there but can’t figure out what it is

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@Topias_Korpi do you have a very low max acceleration?

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@Jason_McMullan No, I’ve got 3000mm/s^2 (10000 works the same). I tried low acceleration and the start of the movement was also bad.

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Most probably you have back EMF on the control pins chech with either logical analizer or oscilloscope.

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An unloaded stepper can behave like that. Try to brake it with your finger, if the problem disappeares everything is fine. You can even feel if the force is high enough.

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@George_Novtekov if that is the case, how can I get rid of back EMF?

@ChPech Okey, good to know. I’ll try that too.

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You can’t get rid of BackEMF but overcome it with higher input voltage. BackEMF is dependand on RPM but your video shows a low speed so I would rule it out.
What can happen with an unloaded stepper is that it basically stops between steps but the rotor has some inertia which means it bounces back at the end of the step a bit. If this happens to align with your step frequency it can even run backwards. See here for example: http://www.nmbtc.com/step-motors/engineering/vibration-and-resonance/

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@ChPech Okay! Thanks for the info! I could try with 24V PSU (currently 12V).

But it’s really weird that this works perfectly when I’m using PC instead of Raspberry Pi…

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So what happened until today? Were you able to make it? Did it worl out as you planned?

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@Sher_Khan I got it running well but don’t remember what was the solution :sweat_smile: It can be that I switched the power supply from 12V to 24V.
The project has been on a side for a while…