My take on a stepper damper

[S_J_H]

I have recently been battling with some bad mid range resonance on my x3 mill. I am using a Xylotex 4 axis drive with 425 oz steppers. I had reduced the resonance by greatly reducing the Vref on the drive. However this is a very poor fix as it hurts performance. I looked at several damper designs used on engines. Elastomer, fluid and a pendulum type. I decided a pendulum type might offer the quickest response and be able to absorb a wider frequency range so I gave it a shot. The results are nothing short of amazing. It completely absorbs all resonance and vibration problems I was having. I was able to turn up the Vref to full power without a trace of resonance with the damper installed. Remove it and the ugly resonance is back. It's dramatic how well this damper works. TCI makes a automotive type of this damper for racing and they call it the "rattler". This is because when it is working you can hear the rollers working. It's very interesting to hear this damper work. At feeds where there was usually resonance the damper will be very active with the rollers making noise while they are absorbing the resonance. At speeds when the stepper is in a resonance free operating range it is dead silent. It's easy to make. My design is about 2.45 in diameter with 9 rollers.The rollers have .045 clearance in the pockets. http://i109.photobucket.com/albums/n...rdamper001.jpg http://i109.photobucket.com/albums/n...rdamper002.jpg http://i109.photobucket.com/albums/n...rdamper003.jpg http://i109.photobucket.com/albums/n...rdamper004.jpg Steve

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[Ninhil]

Thats pretty cool to see you fixed your problems. I'm still a little uncertain as to how it works, but nonetheless it does work, so thats great!

Do you think resonance wouldn't be an issue had you used the 269 oz/in motors from xylotex?

Are you happy with the 425 on the z-axis? I suppose one of my decisions will be to see if a 269 oz/in compared to the 425 oz/in would work better upon the z-axis.

What I'm getting at is perhaps the resonance is a function of the 425's?

[Buzz9075]

Steve, this is cool. While I have gotten rid of most of my reasonance it comes back and haunts me from time to time on some very specific movements. Any chance you have dimensions on parts so that I can create one test. Thanks

[S_J_H]

Ninhil, I have a set of 269's also and yes they do have less resonance for the most part. But they are quite a bit weaker. The 425's with the damper are much stronger. I have no issues with resonance on the z axis. The leadscrew drive is totally different than what I have on my table and it just does not seem to have this problem. For a Q&A on this type of damper I'll refer to a real automotive damper using a similar design.- http://www.tciauto.com/Products/Tech...ttler_tech.asp Buzz, It was brought to my attention I should test the damper without rollers and with the rollers packed so they can not roll. This to qualify the effect is from the action of the rollers and not simply a flywheel effect. I will do those tests tonight or tomorrow and report back. I'll give some measurements at that time. Steve

[ger21]

Do you need to lower your acceleration due to the extra weight on the motor?

[Buzz9075]

Steve, thanks. Think there would be a different if this was made out of wood or metal? While I could make it out of metal it would be more complicated.

[S_J_H]

Well the flywheel effect alone is responsible for about 90-95% of the reduction using my lab quality senses for test measurements . With the rollers functional the steppers are just a little bit quieter and smoother than with them packed tight. With the rollers removed it still has enough inertia to dampen maybe 80% over nothing at all attached to the stepper. A simple flywheel does a tremendous job of eliminating the resonance and I guess I am just late to learn this. The extra work to make this functional damper over a simple flywheel may not be worth it as the motor impulses are weak enough to be damped pretty well with just a simple flywheel. GER21, I ran the roadrunner test code in MACH AT 60IPM and 6 for acel with the damper on and it was the smoothest code I have ever seen with this mill. In other words, no I did not have to lower the acceleration at all. I may be able to raise it now that all the vibration and resonance is gone. Steve

[S_J_H]

Buzz, I suppose it could be made from a hardwood. I think you'll need steel rollers though. I would first try a metal flywheel as that is simple to make compared to this damper and it seems to work almost as well on my mill. But if anybody wants to make one of these roller dampers and give it a try, the specs for the one I made are- body 2.45" diameter 9 holes on a 1.75" bolt circle Holes .505" wide and .625" deep. roller slugs .460" wide and .585" long Steve

[Buzz9075]

Steve, thanks for all the info. I will give this a try this week and let you know how it goes.

[Pres]

Besides being considerably more compact, the above adds to the benefits of a belt drive for steppers.
e.g.
No coupler needed, easy change to flywheel dampening, and minimal alignment problem.

The roller dampener seems really neat.
I wonder about the effect of more weight clearance or using lead
(or DU - i heard it is really heavy & cheap in Iraq)

Thanks for the thread!

Pres

[Apples]

S J H

It's amazing how much of a difference that has made. I'd like to do it on my steppers as well.

My steppers do not have the shaft out the back of the motor. I guess that yours did.

Would it make any difference if I had the flywheel on the other shaft of my timing belt setup no the actual motor shaft? I wonder if it will, because I have a 4" alum. timing pulley there anyway. Wouldn't that alum. pulley do just the same.

I have also replyed to the same post on yahoo groups, dunno if it sent ok though.

Cheers
Peter
Australia

[Jason Marsha]

About a year back I picked a stepper out of a copier with thick laminated metal disk on the end shaft and never knew what it was for, now I do.
I think I destroyed it in the removal but as a diligent packrat its "remains" are lying around somewhere.
I will post a pic if I find it.

Jason

Edit: Found the pic

[Apples]

Would the flywheel idea work with very low rpm's. Say 10rpm?

Peter
Australia

[S_J_H]

Would it make any difference if I had the flywheel on the other shaft of my timing belt setup no the actual motor shaft? I wonder if it will, because I have a 4" alum. timing pulley there anyway. Wouldn't that alum. pulley do just the same

Peter, I tested it both ways and yes it worked equally well on the other shaft. I have a 1.75" pulley on the ballscrew and it does nothing to dampen the resonation. I tried loading the table by tightening the gibs to reduce the resonance before making the damper as I read sometimes that helps. Oddly this only worked for the x axis which is direct driven. It had no effect at all on the belt driven Y axis, tight, loose it made no difference at all. So the loading effect does not seem to be transfered through the belt to the stepper, at least on my machine. But the damper action does seem to transfer through the belt and stop the resonation cold in it's tracks. I found that interesting. Steve

[P.Passuello]

Hi
After reading everyones posts about resonance I thought I would see if adding a flywheel (as I dont have a damper at present)to my motor shaft would help. Sitting on the workbench with no load they only run at 800pps maximum. Anything above this they sound like they are rattling themselves to peices and miss steps, at about 1000pps or higher they would stall and hence I have never installed them. Tonight I connected a weight to the motor shaft and run new tests. With the weight connected I can now run the motors at 5000pps and they work smoothly every time on the test bench. I also note that if while it is running I rest my hand lightly on the motor, (not the shaft) it will stall every time. My theory was to get the motors running on the bench then connect them to a machine but it looks like they won't run properly unless connected to a machine. If I get time later this week I will connect to my current machine and see what happens. I may have been trying to solve a problem that didn't exist.

PS I like the look of the damper shown in Steve's Post. They look simple to make and sound like they are really effective. I look forward to hearing how Buzz9075 gets on with his ones.

Cheers
Peter

[Fixittt]

hi guys very nice thread as I have chased this demond for years.

I was laying in bed wondering....
resonance is essentually vibration that the motor causes.

I have not been able to do it yet, but I want to try sticking a few peices of dynamay on a stepper mottor and see what that does for me.

has anyone ever thought about this?

[307startup]

That is probably the most innovative fix I have seen yet here on CNCzone! Excellent job S_J_H! Did you use some kind of ratio to determine the sizes of your flywheel and rollers?

[OCNC]

Has anyone thought about or experimented with the length of the mounting standoffs in regard to this problem. In other words what would happen if the stepper was mounted directly to the mass of the table in full contact via it's face plate?

Chris

[ger21]

Has anyone thought about or experimented with the length of the mounting standoffs in regard to this problem. In other words what would happen if the stepper was mounted directly to the mass of the table in full contact via it's face plate?

Chris

I tend to think that mounting steppers on standoffs is a bad idea. Even though many people have no problems mounting them that way. The manual for the PacSci steppers I have says they should be mounted tightly to a metal surface, although that's mainly to help draw heat from the motor. But standoffs can't be as rigid as a plate. It also says don't mount the motor where it's subject to vibrations.

[Ninhil]

I tend to think that mounting steppers on standoffs is a bad idea. Even though many people have no problems mounting them that way. The manual for the PacSci steppers I have says they should be mounted tightly to a metal surface, although that's mainly to help draw heat from the motor. But standoffs can't be as rigid as a plate. It also says don't mount the motor where it's subject to vibrations.

well this is interesting.. so if you mount the motor directly to the ballscrew with a flexible coupler, this motor resonance shouldn't be as much of an issue!