I have a single z motor that is having issues. I’ve had the same issue with two boards, three sets of wiring, and three different DRV8825 drivers. So it has to be the motor. The only thing that I can think is that the entire setup is too heavy. The motor that is slipping is the same side that has my CNC shield and Pi installed. Could this be it? Should I be looking for Nema 17s that are stronger than 84 oz/in? Current is currently set to 600ma.
-Ryan J.
Just a note that with the exception of a geared stepper, it seems that 84 oz/in is the highest I can find. I did find a geared with 485 oz/in but I’m not even sure it would work.
84 oz should be way plenty, even at 600 ma, i think. It’s it falling when the stepper is powered on? It’s pretty common for them to drop when they power off. Can you tell us any more about the setup? Anything not ‘by the book’? Maybe a picture or three? Ryan has a video on his playlist of a lowrider handling not only the ‘gantry’ and router, but a couple of steel plates as well.
It’s not really dropping so much as it feels like missed steps while lifting. The motor tries to turn but can’t? Just clicks in place. The only difference between my setup and the stock is that my CNC shield and Pi 4 are mounted to that side’s plate.
And interestingly, my motors never drop when powered off.
They should drop when powered off. So maybe there is too much resistance in the screws.
The pi and cnc shield are not heavier than a rambo and lcd, and are much lighter than the router and power supply, so I don’t think that is it.
I think 600mA is low (that is 0.3V?). I used to set my drv8825s to 0.7V or 0.75V. I also added a fan to them though.
But first, the leadscrews should move smoothly. They need lube, and they need to be aligned well. The spring couplers let you get away with a little off center, but check that the nut holder is pointing the nut to the motor. They gantry should also come all the way down. If something is wonky, it won’t.
I had a similar issue with my Z axis until I fixed the alignment by slightly loosening the screws holding the lead screw nut. After that the gantry drops down under its own weight when power is removed.
Also check your alignment and that you haven’t misaligned the Z tubes by over tightening the XZ bracket. there should be some gap. If tight you may have pulled the top in too much causing misalignment
I’ve loosened the screws on both the nuts and the motors on the Z and still no fall. I’ll check the tightness this afternoon but I’m fairly sure I didn’t over tighten. I tried to keep it snug, not tight.
If it’s still binding, throw some pics of the z assemblies. Maybe someone will spot something.
You have lubricated the leadscrews, right?
Ummm…yes?
No. I thought I had ordered some lube but cannot find it. I’m going to have to find something locally to try.
This is what I have on mine. Doesn’t need a lot.
https://www.lowes.com/pd/Lucas-Oil-Products-8-oz-White-Lithium-Grease/50353744
I got something similar from a bike shop.
Have you tried changing the current in the firmware? It sounds like you’re underdriving the motors.
Different setup entirely, but I am running an SKR 1.3 + 5160’s at 1150ma. When I ran them at lower currents, the motors would hit their torque limit under load and the motor would end up grinding and dropping rather than raising.
I’m running a grbl setup with DRV8825 drivers. I’ll have to manually adjust the voltage. It’s something that I haven’t tried yet. However, my first task is to get the gantry to drop when not under power.
Lube helped. I can now push the gantry down but it still won’t fall on its own. And I did find an overtightened screw or two. One so much it broke part of the XZ main. Now I’ll have to reprint. It’s moving much better. The only problem now is that my left side z backs a step or two after a raise. I didn’t get a chance to check the amperage yet. Going to check that next.
Oh happy day! Reason is the Z was pulling back was because my delay on the motors turning off was 25ms. So the back pressure was causing it to drop. Changed the setting to never turn off the motor. Poof! No more drop. Was having an issue with the Y motor cable wiggling lose, I was running two motors into one JST. Swapped out that setup with a stepper splitter (end fit much better on the board). Poof! No more Y stuttering. Ran a couple of test “cuts” (no router running, just running gcode) and all completed successfully. Tomorrow I’m going to run a test cut or two while my daughter works on her Mother’s Day gift. I’m cautiously optimistic.
Thanks for the tips, everyone.