Stepper Motors Low Torque

Mostly Printed CNC - MPCNC Troubleshooting
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I just got all of the parts together for my MPCNC, but my stepper motors seem to have virtually no torque. I am using these stepper motors:(https://www.ebay.com/itm/Lot-of-5-NEMA-17-Stepper-Motor-GT3-Minebea-Mill-Robot-RepRap-Makerbot-Prusa-S5/321503057192?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649) and using a RAMPS board with A4988 stepper drivers. I am using a 12V 30A power supply.(I think that’s all the details that are necessary)

Anyway, as the title says, my motors have very low torque. I can hold them in place with just my fingers when they are turning(just the motor, with no load), and can easily turn the shaft while they are powered on. My Z-axis is noticeably stronger than my X or Y axes. My Y axis is using the Z-axis slot on the RAMPS board, which has two motor connections. My X-axis is using both the original X and E0 motor connections, so it has two separate motor drivers running it. There does not seem to be any appreciable difference in torque between the two axes, so I don’t know if that is really an issue. The X-axis has a horrendous high pitched whine when I try to turn the current up as far as it can go. Does anyone have any advice for why my motors seem to have no torque?

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Those are on the very low end of what is acceptable.

Did you set your drivers current correctly? Slow is stronger, if you don’t know how fast they are moving that is also an issue.

Have a look through my stepper and driver pages linked at the end of the assembly page.

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As far as speed goes, I am using the Marlin version from here, which looks like it is set to 190 mm/s on X and Y. Even if I have the movements too fast, I wouldn’t think that that would affect holding torque. As far as setting the driver current, I’ve tried both increasing and decreasing the driver current to the extent that the trimpot moves, and that hasn’t seemed to help… Maybe I have bad drivers?

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You control how fast it moves, either through your repetier settings, or your gcode.

 

Steppers are not as strong as you would think, we use two for a reason. Some drivers lower the holding current as it causes unnecessary heat.

There is a very specific way to set them, a little too high or two low and it causes major issues, this is not the place for guess and check.

 

All that said, those are very small steppers and they are used. You have no idea what shape they actually are in or how old they are.

 

1 Like
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Well, it turns out that I had a screw loose. Or eight of them. I spent all this time trying to figure out what it could be electrically, I removed the motors to inspect the ones on the axes to see if they were sound, and… all of my pulleys were loose.

I guess it’s true that you can’t troubleshoot user error out.

 

Thanks for the help anyway Ryan, and I’ll keep it in mind that I should probably upgrade the motors at some point.