Chinese printer - Z Axis skips

Hi guys!

I have bought this 3D printer from Aliexpress about a year ago, and from that time, I have problems with Z axis motors. I hope, finally You can help me!

I don't know what type of controller it has, or what the name of this printer... It has two separate Z axis motors, and those are connected to the same output. From the first time, I had problems with the two motors were not raising the same amount during the printing process. The right side motor moved less than the left side. I had to manually rotate the shaft from time to time to catch up with the left motor. I modified the printer: Added two bearings to the top of these threaded rods, and connected the two rods with a timing belt. Now, they only can rotate the same amount, the belt works well. My problem now has changed: the motors looks weak to me. During the printing, sometimes the motors don't rotate that much what would be needed for correct raising. The final object is lower what it should be, and I can find thicker layers on final product. Sometimes the printing head kicks the half-finished product off from the bed. I tried to find the cause, and found that all of motors are strong as hell, but the Z axis motors are much much weaker. I can stop them with my fingers. If I connect only one Z motor, then I can't stop the motor. When It is stopped (and under power), I cannot rotate it by hand. But when two motors are connected, then I can easily stop them, and when they are stopped (and under power), I can easily rotate them in any direction. It seems to me, the controller can't give enough power to drive the two motors on the same output.

Is it any way to solve this problem? Can I make the output stronger? Use transistors maybe, or some kind of amplifier? Maybe can I use a separate Z motor driver? Please, help me!

BR.
Peter

Most people and kit manufacturers wire two Z motos in parallel, because they don't know any better and RAMPS electronics makes it easy to do [yet another design flaw in RAMPS.] But almost all stepper motors used in RepRaps are better wired in series. Otherwise the driver current is shared between the motors and each one only runs at 50% of the torque of the other motors. Can you read the part numbers on the Z motors, so we can look up their rated current?

Edited 1 time(s). Last edit at 12/15/2015 03:34PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Hi!

Thank you for the answer! Yes, I have heard this series-connecting tip before. I tried it, the motors feels stronger, but yet not strong enough. (currently they are in series) Maybe the printer parts don't fit perfectly, and there is some "stress" in the machine? Sadly, there is not any sign or part number on motors. Manufacturer said, these are Nema 17 motors. That is all I know. I have an USB oscilloscope. Can I use it to measure anyting what can be wrong? Or maybe use it to set the power tuning potentiometer? I rotated that many times in many directions, and I have no idea what would be the best possible setting.

Quote
DeXTeR323i
Hi!

Thank you for the answer! Yes, I have heard this series-connecting tip before. I tried it, the motors feels stronger, but yet not strong enough. (currently they are in series) Maybe the printer parts don't fit perfectly, and there is some "stress" in the machine? Sadly, there is not any sign or part number on motors. Manufacturer said, these are Nema 17 motors. That is all I know. I have an USB oscilloscope. Can I use it to measure anyting what can be wrong? Or maybe use it to set the power tuning potentiometer? I rotated that many times in many directions, and I have no idea what would be the best possible setting.

Personally I think that having to turn potentiometers to adjust motor current is an abomination. Modern electronics lets you adjust the current in software so that you know exactly what the current is.

As you don't know what current you should be aiming for and we have no idea what current you have set, I suggest the following:

1. Swap the Z motor driver with one of the others, in case it is damaged (if so, you will see the problem move to another axis).

2. Never adjust the potentiometer when 12V power is applied.

3. Apply 12V power, exercise the Z motors, then put your finger on the Z stepper driver chip and then on the motors. If the driver chip is too hot to touch but the motors are cool, turn the potentiometer down. If the motors are hot but the chip is cool, connect the motors in parallel instead of in series. If the motors are cool and the driver chip is cool, turn the potentiometer up.

Also check for mechanical issues such as binding leadscrews or threaded rods, and check that you do not have excessive Z movement speed, jerk or acceleration configured in the firmware.

Edited 1 time(s). Last edit at 12/15/2015 04:38PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thank you, I will try this finger temp "measure" tomorrow.
- I have tried to swap outputs before... With one motor connected, it seems ok, but with two motors, the result is the same.
- I have no firmware to configure. I got a kit to assemble, connect it to repetier-host, and use. (I am playing with arduinos also, I have arduino ide, so I think I have the possibility to upload firmware, but I have nothing to upload)

I will report back tomorrow.

Okay, it seems I have found the solution...

I tried to fine-tune the potentiometer, and now the strength of the motors seems ok. I can not stop them by hand. At this time I became suspicious: What if I have no big problem with the power of motors, but the speed of Z motors instead? Can I set the Z speed to low? I checked all the slicer settings, but did not find specific Z axis speed. I did a test slice and checked the G code, looked for the speed of Z movement. I have found a G1 Z [something] F12000. OMG it looks high to me. 12000 mm/min is equal to 200 mm/s. The only setting what was 200, is the travel speed. (I set this setting high long long time ago, to gain print time, and it remained) Now I lowered it to 100, but it is late now, I will try it in the very near future. I hope it was the real problem.

@DC42: Thanks for your time and help so much! I will report the results soon.