Monday, September 9, 2013

MendelMax 1.5 Stepper Motor Upgrade - no more skipped steps!

Ever since the first test prints on my MendelMax 1.5 reprap 3D printer, I've been struggling with skipped steps and layer mis-alignment in my X and Y axis. I've spend much time getting my X and Y axis as smooth and friction-free as possible, upgraded the stepper drivers, and adjusted the acceleration and jerk settings. These all helped, but nothing completely eliminated it. A couple weeks ago I finally decided to try some different stepper motors.

The motors I originally built the machine with were sourced from a industrial salvage yard, and didn't come with any sort of specifications other than they were a NEMA 17 case size and bipolar. (4 leads) I did see someone else's MendelMax with "store bought" steppers and I was shocked at how much longer the cases were and how fast he could get the X and Y axis to accelerate.

So, finally I decided to bite the bullet and purchase a pair of steppers from I've purchased other items from them in the past and they've always had good quality parts. I also bought a 0.35mm nozzle for the extruder as well. The 0.5mm I started with originally seemed "too big", and the 0.25mm I tried next was "too small". I was hoping the 0.35mm was "just right."

New Stepper motor specs:
  • Step angle: 1.8°
  • Holding torque: 55
  • Rated voltage: 2.8V
  • 2 phase
  • Resistance per phase: 2.8?,±10%
  • Inductance per phase: 4.8?,±20%
  • Operation temp range: -20°C ~ +50°C
  • Wieght: 0.365Kg
  • 4 AWG22 lead wires (ends are bare and need connectors)
  • 5mm D-shaped motor shaft

Original motor on the left, new motor on the right
 As you can see, the new steppers are much longer than my original steppers. They proved to have a corresponding increase in torque.

The combination of the new X-Y steppers and 0.35mm nozzle has been great so far. No issues at all with step skipping- the nozzle just blasts through drips during traverses across the part during prints. The printed parts also seem to be more accurate and have cleaner details. I did slightly adjust the voltage going to the X and Y axis using the standard procedure without any trouble. Both Z-axis and the extruder stepper motor are still the original small steppers. I might upgrade the extruder stepper at some point in the future, as I've noticed it skipping steps occasionally. The Z-axis steppers work just fine though.

Swiffer replacement part
One of the first parts I printed was a new, improved design I modeled for a swiffer replacement part. (found on Thingiverse here)  It's a challenging part because of the internal thread to engage the swiffer handle- it requires clean bridging and good accuracy for the threads to fit correctly. The part fit great, much better than previous attempts. This is good because our toddler loves to swing it around and break this particular part. I printed the last attempt using a 80% fill, hopefully that is strong enough to last a while.

New Herringbone Gears
Next up was to upgrade the gears on the extruder. The original straight cut gears were getting noisy with a lot of backlash during printing. I chose to print these Herringbone gears off of thingiverse. They printed very well, and easily assembled. The nut trap in the small gear was very precise, and the nut dropped right in- something I had trouble with previously. The new gears run well with little or no backlash.

I'm considering upgrading the extruder to a belt drive unit and getting rid of the printed gears entirely. A belt drive would have zero backlash, and wouldn't wear out. The 00str00der on thingiverse looks interesting. The only problem is the belts and GT2 timing pulleys are tough to find, particularly at a reasonable price.

No comments:

Post a Comment