Z-axis not working


#1

Hi,
This is my first step in 3d printing.
I can’t have the Z-axis working, when the motors are free they turn properly (and in the same direction), but when I connect the couplers to the lead screws (I’ve got some similar to these ones with 1mm pitch) and try to move the Z-axis the motor are just vibrating and nothing move. I guess there is too much friction for the motors, despite I can turn them by hand without much effort.

I tried to increase the current by turning the screw on the stepper driver (but it can turn indefinitely so I don’t know when it is right, I try a bit further than with the neutral position).

Do you have any advice to help me solve this issue?

Thank you.


#2

Check out the section on tuning current here: http://reprap.org/wiki/Pololu_stepper_driver_board


#3

Thanks. I don’t know what really to get from this link, but I tuned the driver to measure the maximum voltage.
I managed to fix the issue with some lubricant and by moving a bit one of the motor.

I still have an issue; using pronterface I can move the Z-axis from top to bottom with the manual move button but when I press the home button, the motors vibrate and nothing happen.
On other axis, I also got the motors vibrating when homing but after they move to hit the endstop.


#4

Does your printer sound like this

If it does I would love to know how you solved this. This is also my first printer.


#5

Not really, my sound was at much higher frequency.

I solved it by lowering the moving speed on Z axis in Marlin:

#define HOMING_FEEDRATE_Z (4*60)

I changed it to 3*60 and now it works fine.


#6

Your steppers are skipping steps. You should turn up your stepper driver current, using the guide Squid linked earlier.


#7

Yes, I read it but it is still really blurry. I can’t see how it applies here.

They say that you can set your target current by adjusting the screw and read the potential. So far so good but:

  • I don’t know the resistance of my steppers as they say Chinese ones can vary from 0.05 ohm to 0.1 ohm, so it doubles the potential you should read, so you adjust a setting with a potential 100% error, … meeeeh (maybe I can measure the resistance somewhere but it is not said in the guide)
  • 2nd point and more disturbing one. What is my target current? The guide gives an example by setting 70% of maximum rated current to limit heat. Ok, but I just want my motor to turn properly, I will care about temperature later. So, what is my target current?

In practical I tuned the screw to get the maximum potential possible, leading to maximum current and it worked, but it is not satisfying.


#8

Yeah that might cook something!! If they are generic ebay/aliexpress motors id guess they are 1.2A I searched my ebay orders and found the spec sheet - due to complete lack of markings on the motor.

Not sure why you want imdpedance of the stepper - thats not really relevant/useful, just measure vref while it is on and tune until you get the right value.


#9

That’s the thing “the right value”, what is it?
It is where I found the wiki page dumb, it seems just arbitrary.


#10

Assuming you are running 4988s and you stepper motors are 1.2a then vref will be:
1.28.05 = 0.48

Some say you should factor in a safety margin and use 1 instead of 1.2. I havent found overheating to be an issue so I have left it at 1.2.