wierd question.. need help creating virbation resistant stand for a "whole body" vibration 1

[foxfitnessrepair]

first off I dont like the idea of the machine nor do I believe it works but I have been recruited to create something to dampen the vibration. Here are the specs, and max user weight 250lbs
Model: EOS 6600
Commercial Vibration type: Oscillating (seesaw)
Amplitude: 0-10 mm
Color: Silver / Gray
Time setting: 1 minute to 60 minutes / Increments of 1 minute
Speed: 1 Hz to 40Hz / Increments of 1 Hz
Mode: Digital / Analog / Auto
Pre Set Programs: 1-Stand Straight / 2-Knee bent / 3-Push up
Control Panel: Digital display / LED Lights
Load Capacity: Max: 450 Lbs.
Power: 1.5 HP / 120 Volt 60 Hz
Dimensions: Platform: 9” W x 24” L
Assembled: 30” W x 38” L x 52” H
Weight: Net: 160 Lbs. / Gross: 195 Lbs.

Here is what im thinking, not exact and havent done calculations yet but my worries are balance of machine when user steps on it. and height the "plate" will have to be off the floor for total weight of about 450lbs (machine and user total)
Ive attatched rough idea

 

[GregLocock]

10mm at 40 Hz? You'll need a scraper to get the occupant off the platform.

Yes a trampoline is probably quite a good approach, as an isolator. If you want to design it propelry you need to know what floor vibration is acceptable to the other occupants of the building.



Cheers

Greg Locock


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[WolfHR]

Nice point about frequencies, Greg- 20Hz is already in audible range (theoretically) and 5-7Hz is I believe to be avoided*... Would it be a good idea to try to add damping (rubber will have some, but I believe since it's supposed to be used in trampolines, that it will be minimal), perhaps in corner posts (being a luddite, I'd consider using leather on steel friction, like in earliest shocks)?

* I've heard it said e.g. strobes are prohibited to operate at those frequencies- it is in something like brain alpha-wave frequency range and can have quite unpleasant effect on humans: nausea, headaches, even epileptic fits in extreme cases

 

[byrdj]

at $14K for this thing,

http://www.fbewellness.com/alternat...cial-professional-vibration-exercise-machine/

I would think it already has some isolation built into it.
I would think a plate on "motor mounts", then submerge the plate in about 1000lbs of dry sand

 

[foxfitnessrepair]

Thank you for the input, I definately did experience a very strange feeling after using it. The vibration causes a kind of numbness and "sea legs" almost. The vibration is so bad now that im thinking anything less will help. Simply just not a fully thought out design. The customer has tried rubber pads under the feet. Im thinking a more simple solution would be silicone gel under feet. Like a wrist gaurd for computer key board cut into fours, even then im thinking it will just shake off of them. Im seeing my first idea costing upwards of $500 dollars est. with trial and error of springs and welded square tubing/plate costs.

 

[IRstuff]

There seems to be a tendency in most engineers to simply start designing, without an inkling of what their design specifications are. How does one expect to know if they're done with their design when they don't even know what the requirements are?

Vibration "solutions" are a dime a dozen; the question is whether ANY of them will work within the confines of the overall operational requirements and constraints. Removing 40Hz vibrations is considerably different than removing 1Hz vibrations. Attenuating 1Hz vibrations may result in unacceptable sway, using conventional approaches.

One thing you must consider is that energy cannot be destroyed; the vibrational energy of the system MUST go SOMEWHERE. Your trampoline might reduce the vibration to the floor, but that may simply mean that your customer is going to riding a bucking bronco, AND potentially get injured getting on and off the system.

Putting everything on a memory foam mattress might be an alternate solution.

Nonetheless, until you have measurements and frequency response and power spectral densities, you ought to stop with the design and figure out the requirements.

TTFN
faq731-376

 

[rb1957]

is vibration is driven into the platform, right ?

so what effect are you trying to accomplish ? it sounds like 10mm @ 40 Hz isn't it

i suspect it's more the 40 Hz rather than the 10 mm; can you drive the platform at a lower frequency ?

FWIW, i think trying to isolate the "end-user" with silicon pads isn't addressing the fundamental issue.

 

[foxfitnessrepair]

I couldnt agree more. From the floor up I very much dislike this idea. Rubber dampening on shafts connected to board would have worked. Rubber matting under drive motor would help. I thik my best option at this point would be to respectfully bow-out. Its beginning to be quite a project for a bad design in the first place. Thanks for your input everyone, greatly appreciated.

 

[rb1957]

can you drive the platform at a lower frequency ?

 

[foxfitnessrepair]

yes there is lower settings, and vibration is not as bad at those settings but the person manufacturing these machines wants an all out solution at every speed. Thats been the issue because my first introduction to the machine I simply said why not make the max speed closer to the half speed. He went on about needing faster speeds for faster results etc. Hard to believe in my opinion

 

[IRstuff]

Reminds me of the electrical zapper that's supposed to get you a 6-pack or 8-pack abs:

So, if we double the voltage, the abs will develop twice as fast...

TTFN
faq731-376

 

[rb1957]

is there something physiological about 40 Hz ? what about 50 Hz ?

is it the amplitude = velocity (ie too fast ?) ?

 

[zekeman]

10mm @ 40Hz comes to 65g's. I don't think so.
I think you had better get a valid amplitude/ frequency spec first.
And then you could begin the isolation design.

You are looking at a 3 degree of system ( or maybe 2 if you lock the person to the output) which can be managed , given the guy is getting 14K for it.

Surprising they are selling the thing if floor vibration is such a problem.Or are they looking at a new design.

Or am I missing something?

 

[IRstuff]

The vibration to the floor is probably tolerable on a concrete flooring, which would be typical for a exercise gym, which is supposedly the intended use for this machine.

As usual with specs of this nature, you cannot arbitrarily assume that the 10mm amplitude goes with the highest frequency. The power specification would not support that.

Again, you haven't indicated where or how this is to be used. Mass along is very effective at damping vibrations, so placing the machine on its own concrete pad, isolated from the rest of the flooring would be one approach that we would use for our vibration test equipment.

TTFN
faq731-376

 

[foxfitnessrepair]

Very good idea IRstuff, I forgot to mention he happens to be on a fouth floor of an old wooden floored building. I have mentioned to him that I think moving would be the best idea, but he also sells these to people (not sure how many hope not alot) so he was also looking for a commercial application for my solution. Thats been one of the biggest set backs is trying to create something that will look and work well.

 

[zekeman]

On many levels concrete bases are not a practical solution for a homeowner use.s

To get a good solution, one needs to add a mass interface between the machine and the floor, adding another degree of freedom and use spring- dampers between that mass and the machine and to the floor.

Not easy or maybe not doable practically, but doable.

 

[foxfitnessrepair]

definately agree. I was even thinking about adding springs rubber on ea end of springs, under the steel plate on my first "trampoline" idea. for added stability under the plate to keep it from rocking aswell. The trampoline springs would be rubber coated also so there is not much spring noise. I have looked into washing machine vibration plates but they only go up to a max of about 300 lbs.

 

[Strong]

This devise should not be used on any floor above grade! The natural frequency of many types of common floors occur below 40-Hz, so there is potential for structural damage or at least annoyance from resonant structural vibrations. If you are trying to design a passive (springs) isolation system, then you have to consider the flexibility of the floor. You cannot assume the floor, even concrete slab on the ground, is infinitely rigid. For $14,000.00 the machine should have a built-in active vibration cancellation system! Good luck with that!

Walt

 

[Strong]

The trampoline would have no stability for the vertical person on the vertical machine.

Walt

 

[GregLocock]

There's a couple of ways round that.

Cheers

Greg Locock


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