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Hi all,
OK, this might be a bit of an odd/simplistic/amateur question.
Anyway - If I have an object of known mass (around 200grams), vibrating with a known dominant frequency (around 5-10Hz), what else am I likely to need to know in order to try and specify a suitable shock-damper to try to counter-act these vibrations? Max displacement? Velocity? Acceleration?
In an ideal world I would be using shock absorbers from mini radio-controlled cars, as they are readily available, cheap, and the fluid and spring weights can be adjusted. I do realise that I might not be able to get ones for the low weights I am looking at though..
Ta,
Duane.
The best damper is probably going to be determined more by the environment and geometry. Something that in itself has a frequency of, say, 1Hz and some damping.
More definition of the problem would be useful. Is the 200g object the source of the vibration, or is it being driven by vibrations through its support? Can you say what the object is?
Thanks for the reply.
I'd rather not say what the object/situation is at the moment.
The object is currently rigidly attached to a surface which is vibrating at a fairly random frequency response (I am doing Fourier Transforms on this discrete signal to get the dominant frequency). I then want to put spring-damper units between the surface and the object, to try to reduce the vibrations experienced by the object.
or use a tuned mass damper
Thanks, have been looking into them, but trying to keep the mass of the system to a minimum.
Can you mount the object anywhere on the plate? Is there a node that isn't vibrating?
I'm assuming the vibration is normal to the plane of the plate. I was thinking of some form of damped rubber pad, but with only 200g it will have to be very soft to get the frequency down to 1Hz. If you are using Fourier Transforms you obviously are well into the topic so probably know more than I do - but using f = 1/2pi (k/m)^0.5 you'd need a pad stiffness of only 8N/m, and that doesn't seem feasible. 3Hz might be far enough from the driving frequency, but 80N/m still seems very soft.
How much can you allow the object to move relative to the plate, either parallel or normal to it?
try a marshmallow 🙂
It if's no good, eat it. If it works find something non-edible with similar properties.
I know from my own experience, when I tried to mount a action cam to my bike I tried a variety of different spring damper selections from my rc car, they all gave me an improvement in the video quality in some situations but each had points where the video was unusable, my thoughts were that I had found the natural frequency of the spring, but I got bored of the project so never looked into it further.
Not sure whether this helps you but I'm pretty sure my camera was about 220g and the springs were the stock ones that came with a hpi savage,with various different oils, I was mounting to the handlebars via a pivoting arm 15cm long and had the spring damper assembly directly under the camera
^ actually that is a good idea. I had forgotten about those things.
[b]captaintomo[/b]'s link is good - those might have the kind of stiffness I suggested above but thought would be unfeasible (it also gives me some thoughts on how I might try to isolate a GoPro on a kayak from wave motion)
I know you want to keep the overall mass low, [b]Duane[/b], but you might find that adding some mass to the device will make it easier to isolate.
Thanks for the replies everyone.
The vibrating surface is vertical, and vibrating up and down (well, it's vibrating in all directions, but I'm only focussed on the vertical motions).
I don't think soft pads or that wire rope damper will give enough displacement unfortunately (that is something else I am trying to figure out..)
Does this approach make sense - the natural frequency of the spring/mass system should be equal to the dominant frequency of the vibrations (and this can be achieved by altering the spring constant)?
Ta,
Duane.