[S_J_H]

Wow, I have not visited this forum in a long time. Cool to see my dampers had a lot of interest.
I did a lot of testing early on and there was no doubt that any viscous fluid fill in the cylinders reduced the effectiveness of the damper
I have been using these dampers for 4 years now. I have never EVER encountered any resonance since I installed them, and I have thousands of operating hours with them now.

Steve

[Walky]

Well, I'm almost finishing the rebuild of my machine; when it was made of MDF I was getting close to 100 IPM, now it's an aluminum gantry with a steel bed and I'm getting about 60 IPM using the same components. I guess the metallic structure makes if more likely to suffer from resonance problems, so the first thing I'll build will be some dampers. I know the extra weight makes a difference, but I'm pretty sure it shouldn't be this slow considering that now it's stalling under no load at the same speed I was using to cut wood with the old version of the machine. My gantry is made from a long 120mm x 50mm square aluminum tube, and my question is: will it make any difference if I fill it (and the 50x50mm steel tubes from the base of the machine) with foam or some other material in order to prevent echoing and probably vibrations? (not sure if resonance is the right word for this situation).

[RedskinsJBS]

I would fill the tubes with play sand or concrete

[Walky]

I would fill the tubes with play sand or concrete

Wouldn't the extra weight affect the machine's acceleration?.

Is there something lighter that could be used for a similar purpose?. I'm also worried that too much extra weight could damage my 16mm linear bearings and/or the rail mounting bolts (my supported rails are mounted at the side on the X axis).

Can extreme screw whipping worsen resonance problems? My screws are whipping between the nut and the back of the machine (opposite to the motor), because the support bearings (normal bearings) seem to have horrible runout; I have thrust bearings on their way and hope that'll help somehow.

[ger21]

Can extreme screw whipping worsen resonance problems?

The resonance I had wouldn't allow me to go fast enough to get screw whip. If you're have a resonance problem and are able to still go fast enough to get whipping, you probably are using the wrong screws for the application.

[Walky]

The resonance I had wouldn't allow me to go fast enough to get screw whip. If you're have a resonance problem and are able to still go fast enough to get whipping, you probably are using the wrong screws for the application.

The screw is, in fact, too small for my axis (3/8" all-thread and 1200mm long), but I'm aware of that and the reason to use them is local availability (I haven't located a single ACME or trapezoidal screw supplier in the country) and the fact that I already had 3/8" AB nuts at hand. My previous machine (same size, same rails) was made of MDF and the X axis whipped like crazy (worst than now), but I still managed to get near 100 IPM at usable cutting speeds (now I'm stuck at about 50-60 IPM). I tried placing bearings (the same used in the bearing blocks) on a small (20cm) piece of screw and rotating it by hand and it clearly has a noticeable runout from the bearings.

I'll upgrade to ballscrews when I can afford them, but before that I need to fix and sell a defective desktop chinese machine that turned my plans horribly upside down (I hit my head each time I remember that I almost, almost decided to get ballscrews and a VFD instead of this POS chinese crap; well, at least I got a SuperPID so half the problem is solved).

But anyway, back to my point, the fact is that I'm getting very low speed as compared to before, even when being conservative with aceleration, so there must be something wrong going on. So far the plan is to make some dampers and use thrust bearings to see if any of those changes makes a difference. I'm not sure about filling my gantry with concrete (because of my design, sand would fall without making modifications to the gantry), mostly out of fear of getting no difference and instead having to move even more mass around the X axis.

[Rift]

I came across this post on my search to find a solution on dampening the steppers in my Makerbot 3d printer. Its made of wood and at certain speeds the steppers produce a lot of resonance and vibration which flows through the wood like a hot knife through butter.

This makes the machine quite annoying at times.

The steppers on the MB are nema 17s. I'm curious how I could apply something like this to a stepper that has no shaft coming out the back? I think I understand how your design works but am unsure how to apply it to my situation.

Thanks in advanced!

[Steve-Tee]

Hi Rift,


Here is my solution to the single ended motor problem:

http://www.cnczone.com/forums/432326-post101.html


This works by adding a rattler to the motor-shaft coupler.
It might not be quite what you are looking for, but it does eliminate the dreaded resonance problem.

Here's hoping this helps.


Best wishes,
Steve-tee

[the.sniper]

I came across this post on my search to find a solution on dampening the steppers in my Makerbot 3d printer. Its made of wood and at certain speeds the steppers produce a lot of resonance and vibration which flows through the wood like a hot knife through butter.

This makes the machine quite annoying at times.

The steppers on the MB are nema 17s. I'm curious how I could apply something like this to a stepper that has no shaft coming out the back? I think I understand how your design works but am unsure how to apply it to my situation.

Thanks in advanced!

Rift,
Doesnt matter what side of the stepper the damper is mounted on.
Depending on your mounting you might need to get a little creative but
either mount it on/near/in between around the side where the shaft is now or
perhaps think about how much easier it might be if you get some double ended steppers (More money but a quick and easy solution).
Pics of your setup might get some users to post some ideas you may not have thought of yet?
The.Sniper

[Rift]

Steve

Thanks for the reply! That concept looks very interesting and might be what I'm looking for. Do you happen to have any pictures of the parts separated, and also maybe mounted on a stepper.

I'm having a little bit of a hard time making out how exactly it works.

Thanks again!

[Rift]

Rift,
Doesnt matter what side of the stepper the damper is mounted on.
Depending on your mounting you might need to get a little creative but
either mount it on/near/in between around the side where the shaft is now or
perhaps think about how much easier it might be if you get some double ended steppers (More money but a quick and easy solution).
Pics of your setup might get some users to post some ideas you may not have thought of yet?
The.Sniper

I think the biggest issue here is going to be space. Bellow are some pictures from the wiki on building the bot.

This is the Y axis bed which houses the stepper for the X axis.

X Motor Pulley Position | Flickr - Photo Sharing!
X Motor Mount 2 | Flickr - Photo Sharing!
Left Side To Y Stage | Flickr - Photo Sharing!


Here is the location for the Y axis stepper

Body Assembly L-R-M | Flickr - Photo Sharing!
IMG_20101208_194251 | Flickr - Photo Sharing!

And here is the location of the Z stepper. It has a threaded rod attached to it.

Z Axis Motor Mount | Flickr - Photo Sharing!

Also here is a picture with the axis put in place. As well as a video of a little bit of the noise I'm talking about.

http://www.flickr.com/photos/makerbot/5245443174/

[nomedia="http://www.youtube.com/watch?v=JGrr_61UcQw"]YouTube - MOV08212.MPG[/nomedia]
[nomedia="http://www.youtube.com/watch?v=-bTqRT72vvc"]YouTube - MOV08213.MPG[/nomedia]

Space is going to be my biggest enemy.

[Steve-Tee]

Steve

Thanks for the reply! That concept looks very interesting and might be what I'm looking for. Do you happen to have any pictures of the parts separated, and also maybe mounted on a stepper.

I'm having a little bit of a hard time making out how exactly it works.

Thanks again!

Howdee Rift,

You are welcome .
These devices are mounted on the two motors that drive the Y axis of my machine. before I applied them, it was impossible to get the Y axis to complete its traverse without repeated stalling.
Now, it's a different story .

Sorry, I don't have any more pics of this, but I may be able to describe it. It is made from a 50mm length of steel rod, drilled at both ends to accept the motor and the leadscrew.
At the middle of its length, I drilled a couple of holes at 180 degree intervals. These were then threaded, to accept 6mm bolts.
The tyre that runs on this is made from larger diameter rod and is about 20mm long. It has a pair of 7mm holes that the two bolts pass thru on their way to the threaded inner rod.
This results in a shaft coupler with a wobbly bit on it .
It's pretty basic, but the difference it makes it totally out of this world.
You'll find that pretty much anything that adds a rattle to the motor shaft will have a noticeable effect on motor performance.
Give it a go, I think you'll be pleased.


Best wishes,
Steve-tee.

[Steve-Tee]

Hi Rift,


Hmmm, having seen the videos that you have listed, I feel that the shaft mounted resonance damper may not be so helpful afterall.
I am guessing that the noises are coming from panels that are drumming with the motor pulses. Perhaps it's a matter of remounting the motors, so their vibrations are sent into heavier parts of the machine frame?

Either way, great machine. It's really amazing to watch .


Best wishes,
Steve.

[Rift]

Steve

Do you think something like this might be better suited? Iv had some trouble finding a supplier in the US tho.

http://www.astrosyn.com/shopimages/t...0Datasheet.pdf

Iv taken the bot completely apart and have been messing with a few different things. I notice that when I apply downward pressure onto the pulley that is on the stepper shaft the noise drastically lowers. Repositioning them is going to be a bit hard because of the limited amount of space. If I could couple something to the stepper I think that just might do the trick.

[Steve-Tee]

Howdee Rift,

Yes, I think you have hit on the right answer. A device like this will greatly reduce the degree of vibration transfer to the rest of the machine frame.
I suspect that a flywheel will achieve a similar result, by taking the sharp 'edge' of the motor steps. Trouble is, it could also lead to stalling at the moment of a direction change.
To some degree, the downward pressure you applied to the motor shaft is having the same effect as the flywheel would. it's helping to smooth out the individual steps, by applying a dynamic load to the rotor.
Perhaps you could get some degree of relief by adding a heavy steel plate to the front of the motor shell - where it bolts to the machine body. This would shift the resonant point to a lower frequency, so the annoying vibrations will be heard less often.
In combination with a heavier pulley, or a small flywheel, you might just bowl this problem over .


Best wishes,
Steve-tee.

[vger]

Walky,

When you changed from MDF to metal, did you change the way the motors are mounted?

When a stepper makes a step in one direction, there is a rotational force in the opposite direction on the motor frame. If the motor is not VERY solidly mounted it can cause resonance problems.

Steve

[mcArch]

First off, great thread, this is very helpful . . . So let's say I have these 2830oz-in steppers, I'm getting some vibrations throughout the rpm range (0 to 600rpm), and I want to make a damper to go on the 1/4", second motor shaft. My plan is to make these dampers with an aluminum housing, 4.5"od solid alum stock cut to shape on a lathe, then insert a steel "donut", or maybe a series of them so I can vary the weight? & the key would be the rubber gaskets that go between the "donut" & the housing & cap. Probably need some more screws in the cap other than the single center one so it does not back out on me. Is this a good starting point, any suggestions on the amount of weight I would start with for the "donuts"? I figure since the friction force is what is absorbing the vibration, then if I can adjust the friction force by varying the clamping force with the cap screws, it gives me one more level of fine tuning?
Any input would be greatly appreciated.
-
Calvino

[vger]

Actually... although friction may get you some results... a tuned resonance response of an elastic (spring) coupled weight is what you want. As the motor steps, it over shoots (due to inertia of the rotor and attached mass) and then swings back past the final rest position and then forward again decreasing in amplitude each time. Loosly hold a pencil verticly between 2 fingers and rapidly move your hand in a step to the left a couple of inches while observing the top of the pencil. Increase the mass at the top of the pencil and the resonance frequency decreases, while the amplitude of the resonance increases.

If you add somthing to the rotor with a resonance frequency that causes it's mass in motion to counteract the ringing of the motor rotor and attached mass, you have it.

Case in point... a vertical lift pump (200 HP) was shaking at the top at it's natural resonance (mass of the motor sticking up high above the mount) and could not be balanced out. The fix was a solid rod 1 1/2" diameter sticking up above the top of the motor with a 10 Lb weight that was adjustable along it's length. Once it was "tuned" the weight was in motion by about 2" but the top of the motor had less than .002" of motion.

Steve

[mcArch]

Thanks Steve, I see, the mass of the steel rings inside is the more critical part? The rubber gaskets should be thick enough to give some spring action, but would essentially dampen the resonance and absorb the energy as I understand it from the 2 white papers that you posted in #220. In other words, what you are talking about above is a Dynamic Vibration Absorber, but then by adding the "viscous damping" (in this case, the rubber gaskets) like I'm talking about, then we have a Damped Dynamic Vibration Absorber. Did I get that right? If so, then the question remains, without knowing the natural frequency of the motor, can I calculate it from knowing the rotor inertia and rpm range? What about the natural frequency of a rotating steel donut? How do I calculate that? I know how to get the moment of inertia, but not the natural frequency . . . ? & if it's not really feasible to calculate those values to follow through the formulas in the first white-paper listed there, then can I start with some ball-park mass in the donuts & then be able to fine-tune it? I know the mass of the entire motor, & the rotor inertia, but not the rotor mass . . . ? Part of the trouble is that I have to make the DDVA's in my shop here & then take them half way across the country & install them on the machine & don't want to have to completely re-build them out there . . . that would not be too good. Any thoughts?
Thanks for your input.
Cheers . . . --Mike

[Walky]

Walky,

When you changed from MDF to metal, did you change the way the motors are mounted?

When a stepper makes a step in one direction, there is a rotational force in the opposite direction on the motor frame. If the motor is not VERY solidly mounted it can cause resonance problems.

Steve

They're provisionally (until I can machine the parts I need for the definitive mounting) fixed in a way that's not extremely rigid, but not horrible either (4 screws leaving room for the coupler between the motor and the aluminum plate); one of the axis has its motor quite strongly fixed (screwed directly to an aluminum plate) and it was the one with the worst performance. I think the problem might have been the bearing I was using, which were not very straight axialy-wise and thus were causing progresively worst wipping (might have been the lock nuts and the way they contacted the bearings, too, because I got thrust bearings and the angle was still very wrong). I was using 3/8" threaded rod on 3/8" bearings, while the MDF machine used 3/8" rods on 9mm bearings filed to make a tight fit, which might explain the better performance. I might have underestimated how much effect the extra weight would have in the machine performance, too, silly me!.

Anyway, nevermind: I got sick of it, took out some savings from the bank and few days ago I got a couple of ballscrews with mounting blocks (I'll still use 3/8" rod on the Z axis, since it works fine as it is and I added a second AB acetal nut to it, back to back, to further reduce backlash). I'll still make dampers for the machine, though; it can't do any bad.

Thanks anyway


BTW: What about placing a couple of helical aluminum couplings 90º from the motor's shaft (by means of a "T" shaped piece), and take advantage of their springy effect for dampening?. Maybe put a small weight on the other end of each coupler, even a small screw or rod. Or maybe just use a single coupler directly into the shaft, then hold the "T" to it, and then a couple of weights at each end? The first option seems more reliable to me, but the second one might not be as crazy at slower speeds and small weights (so the coupler doesn't bend too much downwards).