Really irritating RepRap problem fixed

The Y carriage movement on my new printer has been very weak. Enough so that though I finished a few small prints, when I tried larger stuff (2 or 3 hour prints) inevitably it would eventually lose torque and destroy the print.

I completely tore the Y carriage down to try re-lubing the horrid linear bearings. No good. I went ahead and fixed the LED and resistor that caught fire under there a couple of weeks ago while I had it open. I broke out the other printer and spent a couple of hours adjusting settings and printing a set of replacement bushings (they print fast but they have to be very exact dimensions).

None of this helped. The motor still was very weak; just slight finger pressure could cause it to jump and miss steps. I replaced the motor, no good. I adjusted the drive current probably 50 times in the last few days. I built a new cable for that section. I replaced the motor driver. None of this helped.

Finally after talking it over on IRC I decided these motors just aren't up to this application, and went out to a RepRap supplier and looked at their motors. Their windings are 2.4 ohms per phase. Mine are 60. There's the problem.

I bought these motors off eBay. They were originally part of some vinyl cutting printers that were damaged (new) and parted out, and probably were intended to run on 24 or 36 volts.

However, I realized that these are center-tapped, so I tried re-wiring one using the center tap 30 ohm coil to make them draw twice the current. This helped immensely, enough that I can now print (I think - I have a 2.5 hour print going as I get ready for bed, we'll see in the morning). The Y motor is getting pretty hot though (67 degrees, too hot to touch comfortably). I will probably order a pair of the proper motors for this application from because though I *CAN* print now, I have to go slow. I'm printing at about 60mm/second. On the other printer I've hit 150 Also I think it may be possible that by using only half the coils I'm getting less resolution.

I also ordered a couple of 5# spools of PLA filament so I can start working on a few prototypes for Duckon stuff.