[S_J_H]

Excellent job S_J_H! Did you use some kind of ratio to determine the sizes of your flywheel and rollers?

Thanks, I searched for a while to look for such a calculation but found nothing. I just sort of guessed based on the size of the stepper motor. Maybe I got lucky. ger21, I have my Y axis mounted to a plate and my x axis on four .75" diameter steel standoffs. The Y axis resonated much worse than my x axis before the damper. The Y axis is also belt driven. My Z axis is also belt driven and mounted on a less rigid weldment plate. It suffers no resonance at all. It drives a 10TPI acme though. Tighten the gib on the x axis and it has a large effect on removing the resonance. Tighten the gib on the y axis and there is absolutely no effect on resonance. There are just so many things that seem to play into the resonance picture. All I know right now is that the flywheel/damper kills the resonance dead cold in it's tracks on either axis. Take it off, and wow, instant nasty loud resonance is back. The rollers are noisy though. When I get the time I am going to try filling the roller pockets with a high viscosity liquid to dampen the roller action and see what effect that has. I realize most of the resonance removal is from inertia of the flywheel. There is no doubt about that. However what causes this resonance is best removed with a real damper. Just like the crankshaft on an engine tends to break over time without a harmonic damper. IMHO a real damper can only help and certainly will have no adverse effect over that of just a simple flywheel. Probably just boils down to how much work you want to invest in the part. I figure, heck with a cnc mill at my disposal I might as well make something a little nicer than just a simple flywheel. Steve

[OCNC]

When you mount the stepper on standoffs you're creating a cantilevered beam (a short one to be sure) but it follows that it's natural frequency will be lower than what you will get if the stepper is connected closer to the table mass. By being closer to the table the natural frequency has increased above the resonant frequency while by adding the weight to the outboard end of the stepper (while on standoffs) the natural frequency has been decreased below the resonant frequency. In either case the problem has been solved (at least for that speed range or maybe you could say 'octave') by adjusting the natural frequency of the system to be out of phase with the point of resonance.

Chris

[Jay C]

How about a with/without set of videos

[S_J_H]

Just an update. There is no longer any doubt about whether or not most of the effect is from flywheel inertia. It is MUCH more effective than a simple flywheel. In my early testing I had thought it was mainly flywheel effect. After much more testing I was able to get the steppers to resonate quite badly with only a flywheel(rollers packed so they can not move). Allowing the rollers to move completely eliminates this resonance. Also filling the dampers with a heavy oil totally ruins the effect and they do not work at all. The rollers must be free to move in the pockets. Steve

[S_J_H]

How about a with/without set of videos

Ok, I'll try and do that later today. Steve

[S_J_H]

ok,
You'll need the latest version of Flash to view these clips.

Clip one shows the Y axis jogging smoothly at 30IPM with the damper installed.
http://s109.photobucket.com/albums/n...t=damperon.flv

Clip two shows how it sounds when nothing is changed but removing the damper!
http://s109.photobucket.com/albums/n...=damperoff.flv

Turn up the volume and enjoy.

Steve :rainfro:

[Jay C]

WOW! Yeah big difference. Thanks

[Apples]

How many motor rpm's do you think that the resonances is happening at?

Your motors are bout 270oz-in yes?

Peter
Australia

[S_J_H]

Peter,
Around 200-300 rpm seems to be the bad spot for these motors/drive.
I am using 425oz motors.

Steve

[Buzz9075]

While I don't get much stalling any more I get this sound alot... which means stalling will happen sooner or latter. Once I get things back together (doing some z axis and gantry changes and adjustments) I am going to give this a try.

[Buzz9075]

Steve,

I got a piece of plastic 2" thick the other day. Put together a draft drawing below. While I still have to figure out how to secure to shaft I figured I would see what you think.

As I don't have a lathe to turn down metal bar, what do you think if I change the diameter of the slugs to a .5 and adjust the holes to .55. Might need a little adjust to the bolt circle to all for room between the slug holes. In the diagram I have put in 2 circles with .55D.

[Jason Marsha]

Thats a big difference allright.

Jason

[S_J_H]

Buzz,
that should work just fine. My first damper I just cnc interolated the pockets with a .25" endmill. On my 2nd damper I cnc indexed the holes and drilled them manually using the quill with a 9/16" endmill.
So I just used non turned .5" stock which gave me .0625" clearance in the second damper. It works just as well.
Good luck! I think you'll find it well worth your effort.Tremendous difference in smoothness.
Steve

[Buzz9075]

Excellent. I am picking up some .5" bar today. Should be able to squeeze machining this in sometime this week.

[twice2]

S_J_H,
I too have bad resonance with 425's.
I noticed just squeezing the motor with my hand would calm it...
Lowering current helped a bit but my mill has little mass.

I did not have a way to test your design in metal so I copied your design in pine. I filled the nine pockets with lead slugs, some rattle, some don't...
I made a cap with recess and 3 screws to hold them in.
I can post the dxf and the sheetcam job it someone wants it.

My results are dramatic - from 2.0 Vref @ 20 ipm to 3.33 Vref @ 43 ipm.
I could go faster but my screws get alittle whippy
I will probably turn the current down a bit as I currently don't need all the torque these motors can deliver, keeps them cooler and less power consumption...

Thanks for leading the way
Best Mike

[P.Passuello]

Hi twice2
Thats some great results you have there. Interested to see that even one made out of wood works fine. I would be like to see your dxf and sheetcam job if you would post them.
Cheers
Peter

[twice2]

I guess one could try filling the pockets with fishing sinkers, lead split shot etc...
Here are my files.

[Oldmanandhistoy]

Just a quick post to say thank you to Steve aka S J H for this thread. It inspired me to do some thing I would not have dreamed of trying before. The results are way beyond my expectations.
Using the resonance damper described here has make my X axis go from unusable (because of resonance and high motor inertia) to a system which gives my 7m/min (275”/min) rapids (machine has more but I don’t want to push it at this stage; still setting it up) of smooth motion. This is with a stepper motor, Trapezoidal screw and a drive with no mid band resonance suppression.
It is a remarkable device that makes drives with MBRS unnecessary imho which every one should know about.
One last thing I made it from 1” MDF with steel rollers just for test purposes and it works a dream. I plan to cut one from aluminium using my new machine.

Thanks again,

John

[S_J_H]

John,
You are welcome! I have not checked this forum in quite some time and just saw this. I am very glad this helped you!
Steve

[S_J_H]

Sorry I missed your post Mike! I am very glad they worked for you as well!

Steve