Friday, March 16, 2007


Darwin's Y-axis repeatability

Firstly, I've been issued with IE7 which means Blogger actually works properly on my computer... I cannot express the joy!

Secondly and more importantly, the toothed pulleys from the previous post were put on the Y-axis. Big thanks to Adrian for sorting out the electronics and the repeatability programming!

Super glue was used to lock the little gears into position on the 8 mm drive bar. [Incorporating flats are on the development list]. The same repeatability test used on the Z-axis (see previous post) was re-used, results below:

After the first ten runs the repeatability appears to be in the ball park of ±0.04 mm. I think that the first few runs balance the tension: this is important because the transmission isn't symetrical:

It's worth stressing that this is not bad, we're still within our targets, but we need more data to pin down excatly what's going on. The next test will need 100+ runs.

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this is cool... i'm really excited to get my own machine up and running soon. oddly enough, i think it would be quite fun to write calibration and initialization routines. wow, i'm a dork. :^)
Zach - if you want to do calibration (it's a filthy job, but someone's got to etc) you'll need a digital linear scale like the one here (I'm sure there are similar US suppliers):

Ed's design incorporates the mounting points for this thing, which is not needed when the machine is operating, of course.
Thanks Adrian, that answers a long held back question but confirms a guess. I didn't see any wires coming from the linear scales so didn't think you were using them for absolute positioning but had to wonder a bit.
BTW, you can get that exact model of calipers at Woolworths in the UK (or, at least, you could a few months ago).
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