Stepper motor noise

[dmparrott]

Just a quick question I was hoping someone could answer.

I've just completed the project of CNC'ing a benchtop milling machine and everything seems to be working fine. I'm running three 495 in. oz. steppers for each axis and one of the steppers makes some noise when stopped. The noise is a very high-pitched whine when the motor has current applied but is stationary. When it starts moving, the noise disappears. I tried to rotate the shaft to see if it was doing this at just one spot on the armature but it does it no matter where it stops. The other two motors are completely silent when not moving. Does this noise indicate some type of problem with the motor?

Thanks for your help.

Dennis

[pminmo]

No it's fairly normal for chopped drivers. Some drivers are worse than others, so motor driver combinations are worse. Some drivers are quiet with certain motors and then the same driver quite noisey with a different motor of different specifications.

[dmparrott]

Phil,

Thanks for your reply. I'm using the Gecko 203 drivers with these steppers and I just thought it was kind of strange that one motor would be noisy while the other two are perfectly quiet. Do you think if I swapped motors around that the same motor would continue to make noise with a different driver or is it inherent in that particular motor? I suppose I could try it and see what happens. Could it also be a setting for that axis in the Mach 3 software that I missed? Has anyone else out there in CNC Zone land experienced this problem?

Dennis

[Mariss Freimanis]

Dennis,

I'm guessing the noise you are describing is a possible workmanship defect in the drive. It does not affect the reliability or performance of the drive, it is cosmetic and simply irritating. If you like, please return the drive for evaluation and write the word "expedite" on the outside of the package. We will resolve the problem and return the drive the same day we get it.

Mariss

[dmparrott]

Mariss,

I appreciate your offer to evaluate the driver and I may take you up on that. I did swap the drive to another motor and found that the same motor continues to make noise with a different driver so I'm guessing it's not a problem with the drive. So now I'm thinking it might be some sort of electrical interference. I am using shielded four-wire cable to the drives. The enclosure I'm using (an old Packard Bell CPU) doesn't allow for much room with for the PS, BOB, drivers, relays, etc. so I was wondering if the close proximity of all the components may be inducing noise on some of the wiring. I could forward a photo of the set-up if that might help to figure out the problem. Thanks for your help.

Dennis

[Mariss Freimanis]

Then it is unlikely the drive is the cause. Motor laminations are impregnated with a varnish and baked in an oven after the laminations (motor body) are stacked. If done improperly, some of the laminations fail to get "glued" together and are free to vibrate minutely. They then will "sing" when the motor is driven with a switching type drive.

I'm assuming the sound is a steady, pure and very high pitched whistle? The sound stays the same no matter where the motor is stopped in angular position? If so, this is the reason and not the drive.

The G203V uses what's called an over-constrained PWM switching topology. Uncompensated, this topology can exhibit a characteristic called double-pulsing. This causes a "chirping" sound if uncorrected. Feed-forward compensation is used in the G203V to prevent double-pulsing and it keeps the drive completely silent when stopped or turning slowly. Again, all of the above has no effect on accuracy or reliability; it is there only to eliminate annoying sounds.

Mariss