Stepper Motor Resonance (Nat'l Freq)

Thread Starter


Joined Mar 11, 2007

I'm using a SLO SYN drive and stepping motor (20-to-80 VDC, 6 A input) to operate a worm gear.
The motor is stuttering at around 60, 120 - and sometimes 280 - Hz, when set on 200 pulses per revolution.
The motor itself (per manufacturer) has a natural frequency around 129 Hz.
Through use of a signal generator and power supplies, I've been able to eliminate all other potential causes of noise.
I am convinced it is a resonance issue.

I cannot use the 1/2-step or micro-step functions of the drive due to my inability to increase the # of input pulses (coming from cmos printed circuit boards).
This is a shame b/c it greatly reduces the stutter each time I increase pulses/rev.

The only other advice the manufacturer gives is to A) wire the motor (8-lead) in series vs. in parallel....did it -- no change... and/or B) use a double-shafted motor and place a silicon disc on the back side.
Got one on order.... 4-week lead time.
But I want to fix the problem now!

My question is regarding a third option:
After looking at the All About Circuits website, I'm wondering if I could use a 1) Low-Pass Filter,
2) Band-Pass Filter
3) resonance filter

I've tried the Low-Pass filter and must've used the wrong capacitor size, as the motor would not turn at all.
Which is funny b/c I used a similar filter on my pulse input to the drive and it did an excellent job cleaning up the ac noise.
Was taking the positive lead of the capacitor and connecting to one of the four leads from the drive, leading to the motor windings.
The other lead of the capacitor was going to ground.
Had tried several capacitors ranging from .5 micro-F to 6 micro-F.
Should I use larger?

Also tried the resonance filter, but did not have inductors large enough.
Read that using the primary on a 120V transformer will work.
I have a 120V isolation transformer.... can I use this?
Not sure if I have enough space for four add'l transformers in my cabinet.....

And where would I place these filters..... between power source and drive, or between drive and motor?
There is 6 amps going into the drive, 1.5 amps going to each of the four motor leads.

Also - what is a good method for determining if I have a good ground?
I put in a couple ground rods (and a hole next to them for filling with water), but how do I tell?
Someone told me to measure b/w AC common-to-ground and DC common-to-ground, but I have an isolation transformer feeding my DC, so my resistance on that side is high.

Did I mention this project has been eating my lunch for almost a month....
I've used this same drive + motor on two other machines and did not have the stuttering issue.


Joined Jul 17, 2007
Which SLO-SYN stepper are you using? Is it a unipolar type? (I guess you kind of answered that with the 8-lead statement ;) )

Do you have a schematic available of the CMOS board that's driving it, or at least a list of signals? Are you using an H bridge chopper driver?


Joined Feb 24, 2006
STOP! You are wasting your time trying to apply an electrical solution to a mechanical problem. The 129 Hz. resonance quoted by the manufacturer is for the rotor and the shaft with no load. Add the mechanical load and the location of the mechanical resonance will shift. The only reliable solution that I'm aware of is to ramp the velocity up to the operating speed and to ramp it back down scrupulously avoiding the velocity wich creates the resonance. Anything else that you do is pissin' into the wind.

What I'm saying is that you need to 86 that controller and get yourself one with a microcontroller that can do the job.

BTW - once you get pat the mechanical resonance, you will run into an electrical one, but at a much higher frequency from 3-5kHz.