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Stepper Synchros?

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Eric HertzEric Hertz 04/26/2018 at 04:074 Comments

https://hackaday.com/2018/04/25/retrotechtacular-synchros-go-to-war-and-peace/

Random thoughts:

Most unipolars I've disassembled don't actually have alternating north/south... which might be better. E.G. North is usually on top, south at the bottom. Then, toothed, a bit like gears. OTOH, if viewed as a projection, I guess they do alternate. And the windings cover both halves...

So...?

I'm 50/50 on thinking this'd work. The other half says both motors would find a steady-state position they'd want to stay in, and trying to rotate one by hand would be resisted, just as if the motor was driven normally; the influence of one's slight flux-change would be minor in comparison to the winding currents. oh, and about 20% that I'm way off... so, 40/40/20, I guess.

Discussions

Morning.Star wrote 04/26/2018 at 05:07 point

Oh wow, thats interesting. Nice one Eric :-)

When I was building my RepRap I had to plug two stepper motors into the same port to drive the screw threads holding the X carriage, so it moved equally on both sides.

When I started rebuilding it for the mill (which is still sat there looking sorry for itself) I joined the cables onto one plug for this because the Sanguino board only had one socket each for the motors. When I went to fit them, I moved one and jumped when the other one moved with it.

I figured it would have been noticed, but I didnt know about synchros and I just filed it for future reference. That was way before Hackaday tho, back when I had a workshop.

So I gather the AC power supply then just increases the holding torque of the motors? The magnets themselves supply the switching pulses, its really neat how that works. :-D

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Eric Hertz wrote 04/26/2018 at 06:04 point

i guess I thought the ac would work similar to the synchro's rotor winding. I guess. not.

one thought is... at really low speeds and really short distances, the current generated by the moving magnet isn't enough to overcome friction, etc,., but, more problematic, really, is the static magnetic attraction between the rotor and the windings' ferrous teeth. detent-torque. so, maybe driving the windings with AC would essentially nullify the detent torque... and, yes, also increase holding-torque in any fractional position.

but, I think you're right that the AC does nothing to increase the current generated by moving one shaft... I kinda thought it would... essentially using alternating current's magnetism to essentially increase the net magnetic force between rotor and stator, thus looking as though, for a non ac-driven setup, the static magnets on the rotor are stronger than they actually are, causing greater currents for the same small motion.

or something.

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Morning.Star wrote 04/26/2018 at 11:07 point

If it moved synchronously with the AC, or the signal matched the 'throw' that might  work. I wondered about that myself but other than the driving-pattern on the coils that already exists I couldnt see a way to use it. Try it :-)

But it was interesting to see how reliably the first motor drove the second providing it was a good positive rotation. Just clicking the rotor round slowly made the second one 'bump' and sometimes turn.

I've tried spinning a DC motor with a generator, that seems to dump energy somewhere and it takes a lot of work to shift the second set of coils. Its probably the commutator switching...

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Eric Hertz wrote 04/26/2018 at 17:38 point

"try it" therein lies one of the multitude of problems. Maybe next month.

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