Tuesday, August 02, 2005


Floppy stepper update - updated :)

Our floppy stepper motor does seem to have enough power to shift the turntable at realistic speeds. Keith, Ash and myself set one up last Tuesday night after hacking it and its bearings out of a floppy chassis with a cutting wheel. Earlier tests were not so good, and we now suspect a mechanical problem with the prototype causing bearings to bind.

We put a worm gear on it and put that in the place of the worm on the turntable assembly. It initially moved in both directions, but very slowly and with only just enough power - it got stuck on a few occasions, even when not driving the screw shaft. Stripping down the turntable and rebuilding some bits of it resolved the problem.

The resolution seems a bit lacking, but we can live with it. The motors have an 18 degree step, and with a 100mm diameter turntable that needs to move at roughly 0.1 degree steps to get 0.1mm accuracy. At the moment we've got that but there is no room for error, and anti-backlash gearing will be needed.

My PIC programmer now refuses to erase PICs under Linux, despite having all the right volts on the pins. Moving it to Suzzy's Windows box allows it to work 50% of the time so I suspect timing issues.

Still, we can drive steppers in both directions at varying speeds with the ULN2003 and we've now got a proper USB-serial connection mounted up on the front panel with terminals leading to the breadboard area. Next step is to mount up a MAX202 chip and get some serial connectivity going.

Vik :v)

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