Actions
Forum Thread Details
  • Replies 15 replies
  • Subscribers 332 subscribers
  • Views 1698 views
  • Users 0 members are here
Related

Prusa Mendel Iteration 2 Stepper Motor Z Issues

Former Member

     So I bought all the components I need to make a PMI2 and put it all together, being sure to measure multiple times so it can be accurate as possible. The only issues Ive had are the electronics, mainly the stepper motors. They're have some slight binding issues which are really apparent on the Z axis. I check all the angles that have to do with it and they are really accurate. I also have the rods lubricated and adjusted the power output to max for the stepper motors. The thing is I don't think that the Z motors are receiving enough power, considering that they are connected together. I've had it sitting for a few months now and I have yet to print anything.

 

     If anyone has a PMI2 or know how I can fix the issue that would be a lot of help. Thanks for taking your time to read this. image

  • Are your two Z motors in-phase or out-of-phase with each other, mechanically speaking?

     

    If you had two motors with pinion gears and they each meshed with a large 60 tooth gear, they (imagine them 180 degrees apart on the big gear) would be in-phase.  If you substituted two 30 tooth gears for the big gear, your motors would be out-of-phase.

     

    If your motors were on opposite ends of a shaft, they would be out-of-phase.

  • I would check to make sure the steppers are wired the same way (even in batches from the same manufacturer, you can find occasional variations), then try applying power to one motor and then its mate - watch for rotational phase or micro-stepping conflicts between each. Binding can definitely be an issue if overly constrained (both ends, etc) when using metal bushings or thrust bearings. You can test by loosening the bearing and allowing it to float while testing the motor. You can also apply small heat sinks to the A4988 chips to help dissipate heat if it starts to work and then stops - thermal failure can be tricky to identify sometimes.

     

    Kirk

  • in reply to Former Member

    So it turns out it was the settings that the software comes with. I have it set to this

    image

    It seems off but it was working.

    the only issue right now is this

    image

    and the temperature was reading something like 375 but I think it was a wiring short. I'll just have to reorder the parts and insulate it better

  • You seem to have covered the basics as far as drive current.

     

    You need to make sure that your Z axis moves smoothly. Both the smooth rod AND the threaded rod should be lubricated.  If you have a design that has a spring loaded pair of nuts on the Z drive, make sure the spring isn't overloaded, it should only have a few ounces of pressure.

     

    Also, on the motors, you should be using coils with no more than 3.6 ohms of resistance per winding.  1.8 ohm windings are better.  I once got some steppers with 8 or 10 ohm windings for a printer build and the motors were weak as kittens, I had to toss them.

     

    Oh, also, make sure you're not trying to step too fast.  Turn it down to 1mm per second max speed as a trial.

  • You should also check to make sure your stepper motor controllers are not configured for micro-stepping (1/4, etc) as the motor has less torque when running with that option on, but some controllers can be configured for smaller steps (than the .9/1.8 degree per step based on your motors) through software or jumpers or DIP switches directly on the controllers.

     

    Kirk