Saturday, March 7, 2009

RepStrap: g-code...

I have been attempting to teach my RepStrap g-code for the past several days as I am waiting for a roll of HDPE to come in the mail. There are several reasons why this has been difficult for me. First, I have not been able to use the off the shelf solution that was written by Mike Ellery and extended by others because of my stepper motors. To save a buck I went with some NEMA 23 knockoffs that turned out to be very disappointing. They do not behave like the suggested motors in that you cannot get them to do a full step. They are also a tad lacking on torque. Because of this I have had to take down the speed a bit and rewrite the step functions to delay between half steps. The second issue I faced was getting the driver boards to turn on at all when following the wiring diagrams for Darwin. I finally figured out that the enable pin had to be set to ground, something the diagram does not show. The third issue I experienced when trying to calibrate my machine. For some reason I have yet to understand, the Y axis requires more steps near 0 mm - 30 mm per mm than it does for the rest of the range. To keep the range consistent I had to move the opto switch in order to set the 30 mm position to 0 mm, cutting 30 mm off of my printable area. After solving these problems my g-code firmware works like a charm.

Here is a picture of my current setup.

The next thing on the list for me to get working is a Dremel milling tool head for milling PCBs. With my RepStrap talking g-code I should be able to mill the stepper motor driver board for controlling my extruder.

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