Thursday, April 12, 2007


Hacking the GM2

I hacked one of my new GM2 gearmotors from 224:1 to 14:1 and replaced the existing GM8 on the y-axis of Tommelise 1.0 with it. With a 12v motor driving it the GM8 drives the famously warped y-axis at right at 70 rpm, which when you account for the thread pitch of the 3/8-24 threaded rod that I use gives you a measured traverse rate of 1.2 mm/sec.

On paper the hacked GM2 with a 12v drive motor should give us a traverse rate of roughly 12 mm/sec given the differences in gearing ratio. Unfortunately, the much lower torque that the lower gear ratio implies meant that when I replaced the GM8 with the hacked GM2 I was able to achieve a measured traverse rate of almost precisely 5.8 mm/sec.

I expect that if I were to break down and order some really straight threaded rods I could do considerably better than that. As well, if I were to shift to a coarse-pitched 3/8-16 threaded rod I could crank that up to 8.7 mm/sec.

I'm not going to replace my GM8s on Tommelise just yet. That would simply throw another variable into the mix that I don't want to have to deal with right now.

Doing a 45 degree traverse using both x and y axes running at full tilt gives you, of course, 2^.5 times those figures or roughly 8.2 mm/sec and 12.3 mm/sec respectively.

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