# stepper motor & frequency problem

Discussion in 'Homework Help' started by tracker, Jun 13, 2011.

1. ### tracker Thread Starter Member

Jun 1, 2011
41
1
Hi guys, i'm trying to drive a stepper (full-step) at a rather high frequency (5kHz).

I was told under load, there are certain 'harmonics' or frequency range which the stepper would just stall and refuse to drive.
I Add that when i drive it at 50 Hz it works.

Is this true? Can someone explain the theory behind it? And how can i find this range of frequencies to avoid?

I tried googling for it but i'm getting inrelevant results (i think harmonics is not the right keyword).

2. ### BillB3857 Senior Member

Feb 28, 2009
2,402
348
I tried to post a link, but couldn't get it to work, so here is the pdf. There is a good explanation of what your problem is on page 5 under Slew Rate. Hope this helps.

• ###### 001_motorbas.pdf
File size:
189.8 KB
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34
tracker likes this.

Jun 1, 2011
41
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thanks broth

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
In addition to those harmonics, you generally have to start the motor at a lower rate and increase to the maximum over time. Check your motor specs, too - some will not step that fast.

tracker likes this.
5. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
5kHz is a mighty zippy step rate - particularly when you don't have access to the motors' specifications.

As Beenthere says, you can't start and stop stepper motors instantaneously - you have to increase/decrease the stepping rate gradually. This is to overcome the inertia of the motor itself. If you have a heavy load attached, that will also impact the rate of acceleration/deacceleration that your motor will be able to handle - and you'll wind up with it just buzzing instead of rotating.

The faster a stepper motor turns, the less torque it will have, due to the amount of time it takes to get the current flowing in the motors' windings - so at some point, the motor simply will not be able to turn any faster, even if you have no load attached.

tracker likes this.

Jun 1, 2011
41
1