Sunday, 19 March 2017

La pieces des resistances

Continued a bit with the red filament, but it didn't go long before there was underextrusion. After +Tim Hatch pointed out a possible electronics problem, I carefully checked the filament after pulling it, and indeed there wasn't really any sign of stripping, nor did the bolt have filament pieces on it. Time to see if I have a loose connection.

Occurs to me I've occasionally had the Z axis move surprisingly slowly, only to go at full speed again shortly after. That could be a microstepping error on the Z axis.

There's not that much information on the microstepping setup on the Melzi, but judging from +nop head's comment on this video, the Z axis microstepping is controlled by R20, and the E equivalent is R24 (Melzi board diagram).

Looking at the resistors up close doesn't reveal any obvious flaws, but if Tim is right, this is just slightly flaky, and that's unlikely to show up.

Interestingly, neither X nor Y has shown any problems like this. I guess I will have to try soldering these two as carefully as possible.

If I can't get them soldered, my alternative is to get them at least into a stable state - by cutting them. That, I think, will turn my 1/16th microsteps into 1/8th, losing some precision in the process. (Or would I need to replace with a different resistor?) I would need to adjust the steps per mm, which is reasonably easy, but would it make the motors run hotter? Require more amps? Make them be able to go faster? I don't know.


  1. The microstepping divison ratio is controlled by some tiny jumpers made with solder blobs on the Melzi.

    The 10K resistors set the chopper frequency and I replace them by zero ohm links to switch into low current micro stepping mode which smooths out the current waveform. Having them at 10K wouldn't cause any major problems. The Motion is just not quite as accurate and smooth.

    1. Whoa, thanks for the warning. I guess. Did some more research.,132279,page=11 mentions MS1 MS2 MS3 as controlling the microstepping, though the diagram linked above only has MS1 and MS2 for each motor. For the Sanguinololu (which is related at least), there's a nice description at I guess they are then the three little blobs showing in a grey box for each motor in - they match up with going to two inputs on the chip, to legs 5 and 6. Looks like they should just all be soldered together, which can be done with brute force. Good.