Tuesday 31 July 2012

Melzi mod

In my previous post: StepStuck I described how Pololu stepper drivers (and the open source equivalent StepSticks) are not configured optimally for the typical motors used for RepRap. Not surprisingly Melzi suffers from the same problem as it just has the same circuit on board the single PCB.

This video is a good demonstration of the effect of enabling the A4988's "low current micro step mode". The Z axis is stepping slowly and you can hear a buzz with pauses in it. When I short out R20 it sounds a lot smoother, but still not perfect.

So I replaced all the ROSC resistors with 0R links.


  1. Do you recommend doing this with standard Pololus for the typical low voltage RepRap stepper motor? Also, is the effect on printing noticeable?

  2. You can't do it with the older Pololus with the A4983 chip but you can with the A4988. I have done it to mine. The only downside seems to be a bit more noise when stationary.

    I suspect it might cause better print quality through smoother motion rather than the extra resolution. I will do some tests.

  3. It is now 2013 - Have you tested your Resistor mod to the A4988 and incorporated into your kits?

    1. Yes my kits ship with those resistors replaced with 0R links.