Stepper Motor General Question

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Peter B - 25 Apr 2010 08:23 GMT

I want to drive a small machine at 120 rpm using a stepper motor.

I could run it direct or by a pully to give a reduction so that the
stepper motor runs faster.

Which will give the best torque to the machine from the motor? Looking
at previous posts the suggestion is that full step is best but how
would direct drive on 1/4 step setting compare with full step and
say 3:1 reduction with a toothed belt drive?

Are there any easy rules of thumb to apply?

Thanks Peter

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Bob Minchin - 26 Apr 2010 08:46 GMT

> I want to drive a small machine at 120 rpm using a stepper motor.
>
[quoted text clipped - 9 lines]
>
> Thanks Peter

You might find the thread "Sizing Stepper motors for CNC"
in this group dated 4th to 6th april 10 useful
Especially the comments made by Tony Jeffree.

I am taking my first 'steps' in using stepper motors so have lots to
learn. You will certainly have to ramp up your drive frequency gently
to accelerate the motor from a standstill to 120 rpm.
I have used a voltage controlled oscillator, VCO, followed by a divided
by 1, 2, 4, &8, so that I can play with microstepping on the driver
module and still get the same motor speed
eg divide by 2 and use 1/4 microstepping gives same speed as divide by 8
and full step.
So far the vco control voltage is slugged with a capacitor to stop the
motor stalling which is simple and effective.

This could all be done with a PIC but I don't have the software
development environment set up at home so mixed analogue/digital design
is more suitable for me at the moment.

Bob

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Peter B - 26 Apr 2010 10:49 GMT

On Apr 26, 8:46�am, Bob Minchin
<bob.minchinREM...@YOURHATntlworld.com> wrote:

> > I want to drive a small machine at 120 rpm using a stepper motor.
>
[quoted text clipped - 30 lines]
>
> Bob

Bob,

I am also taking my first steps but is is interesting to learn.

I want the machine to stop after a specific number of pulses which
depends upon what step I am using from the motor, which is why I asked
the question but it would be 20,000 for a full step. Press reset and
away it goes again. I may resort to just using a position sensor to
count the revs, depends how reliable it is.

That part is working, I have used a 555 as oscillator and 4017's as
the pre settable counters because I had them in stock. I am using a
driver frrom Model Engineers Digital Workshop which also seems fine.

I was thinking about using a VCO as it is difficult to ramp up a 555
so I was going to drive via a belt with a tensioner to take up some of
the jolt.

Would be interested in seeing your VCO circuit if possible? it is
around 2khz depending on the step I use.

Peter

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Bob Minchin - 26 Apr 2010 10:59 GMT

> On Apr 26, 8:46�am, Bob Minchin
> <bob.minchinREM...@YOURHATntlworld.com> wrote:
[quoted text clipped - 55 lines]
>
> Peter

I use a 4046 cmos phase lock loop chip but just the vco section and
connect the phase comparator inputs to Vss.

Circuit is straight from the data sheet. The control voltage is slugged
with series 330 and 10uF capacitor.

In your system you can still count the pluses and when you want to stop,
arrange to short the capacitor to Vss and use the logic VCO enable to
stop the oscillator.

Email me direct if you want to discuss further.

Bob

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Peter B - 26 Apr 2010 13:14 GMT

On Apr 26, 10:59�am, Bob Minchin
<bob.minchinREM...@YOURHATntlworld.com> wrote:

> > On Apr 26, 8:46 am, Bob Minchin
> > <bob.minchinREM...@YOURHATntlworld.com> �wrote:
[quoted text clipped - 71 lines]
>
> - Show quoted text -

Thats a good idea Bob. Just ordered some 4046's to give it a try,
never used one before but the gating facility sounds good. Was
thinking of going the pic route but thats even more learing!

Thanks Peter

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Model Forum / General / Models / April 2010

Stepper Motor General Question