right side z motor stalls

Hello. Both sides of the z axis of my prusa mendel turn freely by hand. they typically move up very well too. Usually when trying to home z or move it down more than a few mm, it binds only on the right side and the left keeps moving, pushing the nozzle into the bed (I should probably move the end stop to the left side). When I manually re-level the x-ends the screws turn just fine. I've gotten through a couple test prints and the only thing related to the z axis that I've changed was slightly adjusting the steps for z. It doesn't seem like anything is wrong with the build. The screws are threaded rod and aren't arced or marred. Does anyone have any suggestions on where to look into the electronic side of this to point me in the right direction? Using marlin, ramps 1.4. Thanks!

Have you set the reference voltage for the Z axis? It might be too low.

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I had the same exact problem with my Prusa i2, and it turned out to be a loose wire, so I would recommend double-checking the wires to that motor, ensuring that everything is attched and solid. It could very well be low stepper voltage like 3dkarma said, too.

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I'm going to rewire when i get home from work tonight. I should have some 4 pin connectors in the mail today. Is there a down side to just connecting the two steppers to the shield individually? The board has two spots for z below the driver. I know the voltage is up high enough, that was the first thing i messed with to see if maybe one side couldn't power through a rough patch due to lack of torque. I'll update with any progress. Thanks for the advice

with both z steppers individually connected to the board they both go up without a problem and they both stutter going down. So instead of one stuttering and the nozzle crashing into the board, they both vibrate coming down in tandem. They make a lot of noise and when starting a print the nozzle doesnt come back down to home and prints way to high. The voltage seems ok, and the build still seems solid. I'll have to keep on checking in that the wiring is correct.

Perhaps the stepper driver is damaged: try swapping the driver with one to a different axis, if the z axis then works, the stepper driver may be the issue.
I would also double-check the firmware to make sure the homing feedrate isn't too high. Have you tried lowering the axis manually? does it only stutter while homing? if so, that may be the problem. Try sending it something like G1 Z1 F100, (from a higher position) and see if it still stutters. (the idea is that the feedrate might be telling your stepper to go faster than the stepper can actually go, resulting in your problem)

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Have a read of this thread - it may help. I don't know what board you've got, but it may be that the Z motors are connected in parallel, in which case the ref voltage will need to be double what you may otherwise think. The point the thread makes about the sense resistors is important, too. Check the specifications for your stepper drivers to make sure you're getting the correct reference voltage based on the correct value for the sense resistors. A common mistake is to have stepsticks but set voltage for pololus.

Also, consider slowing the speed. I've had problems before pushing too high a speed on homing, causing the Z axis to bind. That being said, I've also had problems with wiring, causing the exact same problem you described at the start of the thread.

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What machine have you got Dafeesh?

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Waitaki 3D Printer

waitaki, It's a prusa Mendel that I started a couple years ago and finally got back around to. I've been busy with work so I haven't gotten around to trying any if these suggestions. Will update soon.

Homing feed rate appears to have fixed it. I'd be in a jam troubleshooting without this community. There are a lot of variable that a noob like me wouldn't think to check. But they are mistakes that I probably wont make again. So thanks again people