Friday, November 24, 2006


First open-loop coordinated XY-axes pencil tests...

This morning I reprogrammed the 16F877A to run both x and y-axes simultaneously so that I could get an idea of what problems I had remaining to solve in the mechanical design. The gearmotors were run in pseudostepper mode but with open loop speed control, that is, there was no feedback from the encoder chips to stabilise the gearmotor performance.

The tests were done with a 0.5 mm mechanical pencil on paper taped to the glass work surface. The paper was then removed and scanned in black and white at very high resolution so that it would be easier to see non-linearities in the drawn lines that my eyesight might miss looking at the paper in its original state.

When studying the output keep a few things in mind. First, the 0.5 mm mechanical pencil was not rigidly connected to the Mk II. Part of the nonlinearity that you see at the turns is due to that. It also accounts for the break in the path of the upper left hand direction change on the picture.

As well, some of the direction changes were done with mechanical switches rather than software and are marked as such.

As best as I can see there is a little bit of stepping non-linearity, a little bit of non-linearity caused by burrs and unevenness on the poplar guide boards for the x-axis and probably some other non-linearities whose causes I haven't begun to understand.

The next step will be to sand off the x-axis guide boards a bit more carefully and install the x-axis limits switch and the x-axis shaft encoder.

Saw this the other day but didn't get the chance to comment! Nice, looks real promising. Given the accuracy of the extrusion head and bead diameter at the moment, not a whole lot of jitter going on. :)

BTW, where has everyone else gone??
***BTW, where has everyone else gone??***

I haven't got a clue. It's got very quiet lately.
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