Friday, December 05, 2008


Building a printable stepper for a next generation Reprap

In which your narrator gets down to cases in the quest to design and build a more or less printable stepper motor... do you want to read more?

Wow, this is one of the final barriers towards pure self-manufacture... nice one Forrest, and good luck
Thanks, eD. A wow from you is something I really treasure! :-)

It gets lots better than this, though. While I was getting my head around this kind of motor I realised that UNLIKE regular stepper motors it doesn't need polarity control on the windings. As a result you can run the one I'm designing with three standard power transistors like the TIP110 that everybody is familiar with. While the TIP110 will handle 2 amps/winding, way back when I bought a sack full of BD681. Those are rated at 4 amps. :-D

I've been corresponding with Chris and he gets the same impression vis a vis not needing controller chips.

If this thing works it's goodbye L698N. :-)
Much better to use MOSFETS as they don't waste 2V and get hot.
I'm pretty sure that I've got half a dozen lying around here somewhere. I toyed with the notion of making a high amperage stepper controller from discrete parts at one point and bought most of the parts. :-)
Yup, I remembered correctly. Got 6 MOSFETS. HUFA76419P3's rated for 20 amps and 60 volts. That's serious overkill, but what the hell. I've had 'em laying around for years now.

Thanks for the heads up, Nop! :-)
Yes they should do the job without the need for heatsinks.

It is a good idea to put a resistor in series with the gate, say 1K :-

It limits the current the PIC has to provide when charging the gate capacitance.

It slows down the switching slightly. You don't want really fast edges when driving a stepper as it just gives more switching noise.

It can also reduce a tendency to oscillate when the gate is driven with a low impedance.

Of course don't forget the back EMF diode.
LOL! A sketch would be useful. I am an AMATEUR, you know. :-P
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Ah! As they say, a pic is worth a thousand words. :-D

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