I just started collecting data on a few DC motor which drive gearboxes. I have noticed a peak in the higher frequency rang that I am unfamiliar with.

There is a peak at 61472 cpm with dominant sidebands of 6X the rotational speed of the motor. It also has sidebands of running speed and 2X running speed, depending on how you look at it.




I am not an expert when it comes to DC motors and was wondering if any of you have seen this.

Sorry for the poor images. I haven't figured out how to upload them correctly yet.

Red

For some reason, it didn't post my whole question. Sorry for the poor image. Apparently i didn't do it right. See the images here http://maintenanceforums.com/eve/forums/a/tpc/f/3751089011/m/8191030782


I am not an expert when it comes to DC motors and was wondering if any of you have seen this.

Is it gearmesh frequency at 68 orders? 6X sb, hmmm! not sure yet.

I suppose anything is possible. But, it is most dominant in the Motor Outboard Vertical position. Then the Motor Inboard Position. I do not see it at all in the gearbox.

The data I presented is on another unit that is similar and showing the same pattern. The one with the problem is at .1 in/sec (61474 cpm) in the motor outboard vertical position with the next highest peak at running speed (.015 in/sec)

Red

Red
this frequency is collector bar pass, and 6x may be related with retification power supply.

Ricardo Góz from Brazil

Good Morning,
A few questions: Can you see the commutator? Is the motor using tach or armature feedback? Does load effect the amplitudes?
I agree with Ricardo; the first thing I thought of was commutator bar pass.
Thanks and have a good day.

Jeff

Unfortunately, I will not be able to answer these questions until the next collection. But I do appreciate your input.

I am pretty sure there are more than 68 commutator segments. Could it be commutator segments divided by brush holders, or something like that? I suppose it could be. We will check this out during the next collection.