Stepper motor control

Ugha

I've recently discovered stepper motors and how easy it really is to use them.

This has left me a few questions that I haven't been able to look up the answers to
on the 'net. Most are just things I'm curious about but some I'm concerned with.

1: Does running a stepper motor at a far lower voltage harm it or just reduce its power?
·· (I'm running a 24v stepper at 5v)
2: Besides losing sync with the controlling software, does "missing a step" due to the
·· load not moving or being too heavy to move, harm the stepper in any way?
3: Does running a unipolar stepper as bipolar (I THINK that's what its called when you
·· don't use the common ground line and just use a 5-wire stepper as if it is a 4 wire)
·· harm it or have any downside? Does it reduce torque or power?
4: I think I read somewhere that steppers are brushless. Does this mean that they have an
·· extremely long life compared to normal hobby DC motors?
5: I don't have an O-scope and my meter is too cheap to register the fast changes... What
·· kind of power is generated from a stepper when you attempt to use it as a generator?
6: Is it possible to detect in software when a stepper loses sync or misses a step? (higher
·· voltage draw or something like that?)
7: Is there anything else about steppers that I should know or do you have any helpful tips?

Thanks [noparse]:)[/noparse]

T Chap

Ugha said...


1: Does running a stepper motor at a far lower voltage harm it or just reduce its power?
(I'm running a 24v stepper at 5v)

What harms a motor is overcurrent, but yes you'll have less power at lower voltages, best to have voltages higher than the voltage rating, but use current limiting, usually with a method of 'chopping' the current at a threshold with PWM cutting the power to each coil when it exceeds the current set point.

2: Besides losing sync with the controlling software, does "missing a step" due to the
load not moving or being too heavy to move, harm the stepper in any way?

No

3: Does running a unipolar stepper as bipolar (I THINK that's what its called when you
don't use the common ground line and just use a 5-wire stepper as if it is a 4 wire)
harm it or have any downside? Does it reduce torque or power?

Can't use a bopolar driver on a uni motor and vice versa.

4: I think I read somewhere that steppers are brushless. Does this mean that they have an
extremely long life compared to normal hobby DC motors?

Steppers use an external logic for turning on and off each coil, so yes they should have a longer life versus a motor with brushes that can and do wear out.

5: I don't have an O-scope and my meter is too cheap to register the fast changes... What
kind of power is generated from a stepper when you attempt to use it as a generator?


6: Is it possible to detect in software when a stepper loses sync or misses a step? (higher
voltage draw or something like that?)

The easiest method is an encoder on the shaft, move one step = X steps on the encoder. There are sophisticated drivers and techniques that can determine what phase the stepper is on, based on the reverse flow of electricity, but these are hardware based, not software.

7: Is there anything else about steppers that I should know or do you have any helpful tips?

Bipolar is better for power, and requires a dual Hbridge type driver... versus 4 transistors only required to drive a unipolar.

Thanks [noparse]:)[/noparse]

Ugha

Thanks so much for the info TChapman!

I'm curious about how you said I can't use a bipolar circuit on a uni.

I've got two different steppers I salvaged out of a printer.
One has 4 wires and is very easy to drive by simply applying +5 to two wires and ground to the other two, cycling through them
like this makes it run pretty good.
I reverse the order the wires cycle through and the direction changes.
I believe this is a bipolar stepper as there are only 4 wires.

My other stepper has 5 wires, the center is a common ground (the resistance is half that of the others) so I believe that means its
a unipolar stepper.
When I connect the unipolar to the exact same circuit and leave the ground disconnected, this stepper runs as well (although with
quite a bit less torque.

This is just after a bunch of experimenting with a BS2, an H-bridge and my steppers. Please don't be afraid to tell me I'm completely
wrong with my theories as to what kind of steppers these are.

I'll post the extremely simple BS2 code and/or pictures of the steppers if needed.

$WMc%

Ugha

I posted these same "?'s" about a year ago.I know its a pain to look up old posts, But the anwsers are out there.

_____$WMc%________

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