Z Axis And Bed Fall On CoreXY

Core XY Printer
Marlin Firmware
MKS Gens 1.4 Board


I recently built a CoreXY printer got it up and working but only problem I have is the Z axis falls down to the bottom when the power is disconnected it seems the stepper is holding it up in place when the power is on but once its off the z axis comes crashing down I have no problem homing and moving in both directions I'm not sure if its a mechanical issue ( loose slider bearing ) or firmware feature I could change in marlin . I noticed a #disable stepper Z when not being used option but not sure if this would imply for me I've also observed sometimes when the z axis is all the way up if I leave the printer on idle after some time it would drop and come crashing down. any help would be appreciated on this topic thanks in advance

cheers

You dont want to disable an energized stepper in that setup for the Z axis. Heck I dont disable any of mine while powered on unless I turn them off in pronterface.
At the end Gcode put a line in there that moves the bed all the way down. That way, when you power down the machine then its already down there.

Also if the bed dropping when powered off is a concern, you can look for a stepper motor with higher detent torque (holding torque when not energized) as well as look into setting up a compound pulley to increase that torque. Get the numbers right and it might not move at all when powered off. Check out the talk of the compound pulley in this thread here.

This is a feature of a belt drive Z-Axis
Stepper does not hold without power on coils
keeping power on coils to keep table in position --- hot motor

Solution: Stepper motor with brake

VEXTA ORIENTAL STEPPER MOTOR PH 264M-31-C25 4V 1.1AMP WITH BRAKE CNC

[www.ebay.com]

or a servo/lever to lock it in place somewhere.

I guess this is why more people use the threaded rod z axis haha I will try to install a compound pulley for the time being If that fails or doesnt work out worse case ill pull the z axis off my old prusa i3 and mount it instead

If you did it right. The compound pulley would multiply the detent torque and could support the bed unpowered.

For example. The Tripple Length Nema 17 located here has a detent torque of 3.5oz at 1 inch away from the center of the motor shaft

If you setup a compound pulley similar to the Double Tackle shown here, that would quadruple the detent torque to 14oz. Convert to grams and it should be able to support 396 grams without falling, when unpowered.

If you did a geared stepper motor or made your own gearbox, or even a Nema 23 with a higher initial detent torque, you could get away with less pulleys and less belt.

Edited 1 time(s). Last edit at 09/07/2016 07:38PM by FA-MAS.