Re: [CAD_CAM_EDM_DRO] Bipolar vs Unipolar vs Chopper Driver

I'll try and describe it... (it's late, and words may fail me :-) ).

Bipolar and Unipolar motors are the two basic types of motors.

In (most) bipolar steppers there are two coils, or windings. To make the
stepper move you alternately apply power to each coil, reversing the
polarity each "step". Hence bipolar, having two poles, or switching between
two poles at least. A bipolar stepper has four wires (generally).

A unipolar stepper has four windings, which may or may not be connected
together internally, giving 6 or 8 wires. To make the unipolar stepper move
you common up one end of all the windings (in some cases this is done
internally) and connect the other end of the windings to the driver,
alternately turn on one coil at a time (or two if half or microstepping) and
it moves around. You only ever apply the power one way to any given coil,
so hence unipolar, or having one pole.

It all gets a bit messy from there on in, as you can drive most unipolar
steppers in a bipolar manner, but not visa-versa. In general a bipolar
stepper (or a unipolar stepper drive in a bipolar manner) will produce more
torque for a given input power than a unipolar motor.

The "chopper" refers to the electronics in the driver, and can refer to
either a unipolar driver of bipolar driver. Boy, this description could get
long, I'll stop while I'm ahead. There are some excellent tutorials on the
net for stepper theory, have a look at http://www.cs.uiowa.edu/~jones/step/
which is the only one I can find in my bookmarks, I'm sure you could find
more if you hit the search engines.

Cheers, Chris.

* Design engineer, Assembly worker, Cleaner.
* Ohmark Electronics. PO Box 5302, Christchurch, New Zealand.
* http://www.ohmark.co.nz

----- Original Message -----
From: John Guenther <jguenther@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Saturday, September 30, 2000 11:11 PM
Subject: [CAD_CAM_EDM_DRO] Bipolar vs Unipolar vs Chopper Driver


> Ok, here is my question for the week.
>
> What is the difference / benefits between bipolar, unipolar and chopper
> drivers? I see lots of advertising for each type, what is the best type
for
> small machines using NEMA 23 or NEMA 34 stepper motors?
>
> Thanks in advance
>
> John Guenther
>
>
>
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