Question regarding vibration damping - Page 2 - PeachParts Mercedes-Benz Forum

Botnst · #16 09-17-2007, 10:14 PM

Quote:

Originally Posted by Brian Carlton

With a two bladed prop, I'm not grasping why you wish to isolate the frequency of 2250-2450 Hz? Operating engine speed is approx. in the range of 2500 rpm.........correct? With a two bladed prop, the desired frequency would be approx. 83 Hz.

Your plan to isolate via pads on the clamps and/or table should be effective.........however, I believe you'll need to use rubber of a specific durometer to address the specific frequency that you seek. I don't think you'll need fluid filled mounts to achieve a measure of success.

CJlipps already pointed-out the hz vs rpm mistake, for which I am grateful.

If you can direct me to a source of information and material that you describe, I'd love to talk to a tech that knows the product.

Botnst · #17 09-17-2007, 10:19 PM

Quote:

Originally Posted by KarTek

Here's a picture of a rig I made my buddy years ago for him to run a video camera in a helicopter. He just strapped it in the seat next to him. Make the "U" shaped piece under the camera out of 1/4" steel to increase the mass of the camera. The frame is SCH 40 1.5" PVC. For the suspension, simply use bungies. You'll have to wrap them tightly to keep the camera from wallowing and nodding. It's just a matter of experimenting until you find the combination that works. To tighten up the bungies, simply wrap more turns around the frame. Drill a 1/4" hole in the bottom of the mount and use the tripod mount hole in the camera to secure it. This makes it easy to remove and to operate the controls.

Maybe some version of this will work for you.

Somebody else suggested the bungie thing and we have certainly considered it. I'm surprised that it worked for you: We had thought that the buffeting of the aircraft would result in chaotic acceleration of the camera. But as you describe it -- tightly wound -- I can see that it would work. I'm also relieved that it worked in a helicopter. My one helicopter experience reminded me of a vibrating bed in a cheap hotel in Thermopolis, WY. Not that I ever stayed there, 0f course. But there was a whole lot of uncivilized shaking. It was a helicopter back in the olden days, so maybe they don't "whump-whump" anymore.

Brian Carlton · #18 09-17-2007, 10:22 PM

Quote:

Originally Posted by Botnst

CJlipps already pointed-out the hz vs rpm mistake, for which I am grateful.

If you can direct me to a source of information and material that you describe, I'd love to talk to a tech that knows the product.

The best source for such devices would be Lord. If you know the frequency that you wish to absorb.........they've got a material for you.

http://www.astrotex.com/lord.htm

KarTek · #19 09-17-2007, 10:25 PM

Ths trick is to get the mass of the camera up so that it's more resistant to acceleration. If the U mount isn't heavy enough, screw on some deep sea fishing weights. You may also have to add more bungies to dampen movements in more directions than just the basic 8.

Botnst · #20 09-18-2007, 01:22 PM

I posted the questions to an M.E. forum yesterday and it followed a more rigorously mathematical, but similar trajectory to this one. My brother looked over their math and dismissed it as overkill (or just wrong in one case) to demonstrate what he thought was intuitively obvious.

The consensus over there (so far) is there are several vibration-damping materials and designs that should work for the frequency range involved. Choose one and adjust the mounting empirically. If the mat is unsuccessful then go to the fluid-damping. I'm thinking anything more engineering-intensive is simply not worth it, given the flight envelope and data stream we seek.

When we get things going I'll post some pix. Maybe in a week.

B