Sunday, March 02, 2008


Curiouser and curiouser

For those of you who haven't been following my little oddyssey recently, some time ago I put aside my little shaft-encoded gearmotors and decided to give stepper motors a go. Rather than use the 1.8 and 0.9 degree step angle NEMA 23 behemoths that Darwin uses, however, I decided to see if I could make do with much smaller and cheaper 15 degree tin can (permanent magnet) steppers. Smaller motors meant less amperage requirements and cheaper drive electronics.

I wanted to continue to use a threaded rod drive system, which meant that I didn't need the resolution that the small step angle steppers could give. Fifteen degree steps with a 1 mm pitch threaded rod got me a 0.042 mm resolution, more than what I needed.

Bigger steps meant that I had to use fewer steps to get places which meant that I could run the stepper motor at lower stepping rates which meant that I could get more effective torque out of a given motor.

I was able to test my first tin can stepper on my old Tommelise 1.0 controller board. It seemed to be giving me everything I had hoped for; adequate torque, great speed, good resolution and cheap, simple electronics electronics.

About that time I got my first USB-friendly PIC chips, the 18F4550 and was impressed with what it could do as well. Thus encouraged, I put away my old Tommelise 1.0 board and went at doing all my development work with the new, USB-friendly PIC board.

That was when things started to get sticky.

(Read the whole story)

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