Stepper Motors Unipolar in Bipolar Mode

Hey everyone.

I have a stepper motor with 6 leads, using shift registers and transistor arrays.
I need more torque however, so I'm thinking of changing it leaving out the 2 centre taps and driving it in bipolar mode using the MC3479.

Would ignoring the centre taps give me the increased torque advantage of using a bipolar stepper motor?

Thanks!

> Would ignoring the centre taps give me the
> increased torque advantage of using a bipolar
> stepper motor?
>

Driving such a motor in bipolar mode would inherently give more torque due to the fact that twice as much coil is energized at a time.
It probably won't do wonders though, but at least you'll learn smth. by doing it, so it's probably worth a try,

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~/= Marius

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Stepper motor ratings are for a given temperature rise, i.e. power, so when you use two coils instead of one you still need to observe the maximum power rating.

Powers is I^2 x R so when you double R by using the whole coil you have to divide I by sqrt(2), i.e, 1.4, to stay within the power rating. The voltage needs to increase by 1.4.

Because the magnetic field is proportional to ampere turns it will increase by 1.4 as you have doubled the turns but reduced the current by 1.4.

Torque should increase by the same amount, but I have read that the magnetics can become saturated and not give the increase you expect.

Inductance is proportional to turns squared so you increase it by 4. That causes the torque to fall of with increasing speed 4 times quicker when using a constant current drive, or by 2 when using constant voltage (where the time constant is L/R).

Edited 3 time(s). Last edit at 02/14/2009 07:41AM by nophead.

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[www.hydraraptor.blogspot.com]

Hi,
can you send to me an informations about the all kinds of step motors and all about it ( with photos)

thank you

fares