Shaker Load Capability

[sidbrazil]

Hi,

I have a little question. We are intending to use a small shaker (ButtKicker LFE), the supplier was very limited information available:

Frequency response: 5-200 Hz
Nominal Impedance: 4 Ohms
Power Handling: 400 Watts min.

Through the whole range of frequency the amplitude of acceleration intended is: 0,1 g-peak

Based on these information, is it possible to calculate the allowed mass?

Many thanks

 

[IRstuff]

Sure, why not? 1/2mass*v^2 is the KE as a function of time. The derivative of that equation is the power. v is a sinusoidal function of frequency and displacement.

TTFN

FAQ731-376

 

[GregLocock]

No it isn't. No you can't.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Co]

You need at least the distance the shaker moves the mass. For example, a simplified calculation results in an answer of 40.77kg in mass for a 0.5cm lift distance at 100Hz with 400Watts. If you turn up the freq you lower the amount you can lift. (this all assumes that you are lifting a couch) Although, I believe 0.5cm is probably too much for an apparatus like that. For a few mm in distance and a bit more power it could lift well over 200kg.
just a thought,

cheers,

 

[GregLocock]

Coppola-

That doesn't make sense dimensionally or anything else, and certainly doesn't come up with a credible answer for a 5 inch diameter shaker.

5mm amplitude at 100 Hz is around 150 g rms, is it not? So you'd need a force of 60 kN for your 40 kg mass. That's around 6 tonnes. I've never used a 6 tonne shaker, but I've seen them ,and it would be a 2" dia hydraulic ram, and would not hit 100 Hz.

sidbrazil

0.1g pk at 5 Hz is a displacement of 1mm peak, probably within the displacement limits.

Your spec doesn't help much as you need to define what mass you want to accelerate, not just the acceleration. You also need to know some details of the internals, turning a power capability into a table acceleration is not really practical by guesswork. IRstuff's equation is more along the lines of how much power would be needed for a certain mass and velocity, as a MINIMUM, it would be a very optimistic estimate for any commercially available system.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Co]

Greg-
Ok I will not contradict you here. Maybe I misunderstood the question. If so, maybe you can enlighten me.

I don't know any specs about the shaker in mind, I assumed that the maximum energy it needed to produce is to lift that MASS (in the face of gravity) in a particular time of 1/100s. And so, I assumed F is just F=mg. I just converted the energy required to lift a MASS a distance I just made up (5mm) into power. Done deal 5 second calculation.
Whether this information is valid for the particular case I don't know. But from the information provided, with an added parameter of distance it is possible to estimate a MASS (like I said, based on it being able to lift this MASS in the face of gravity in a particular time period)
I treated it like a basic physics problem. I know that in order to obtain a credible result we would need more information about the device I just did what I though might help.
Is there something I misunderstood? If so, please let me know.

Regards,

Coppola

 

[Co]

Actually I did a bit of reading. I figured out my assumptions do not apply here. Sorry for the inconvenience.

These help the situation:

A*(2*pi*f)^2=max accel.

Power=Re(F*v(w)), where v is the Fourier spectrum of the exciter velocity

cheers,

 

[jimkinney]

This device is designed to shake your chair in response to the low frequency channel in movie tracks, so you can feel the bass.

http://www.thebuttkicker.com/ButtKicker Brand Technology/index.htm

I doubt that it would come close to 1g with no load on it.

Jim Kinney
Kennedy Space Center, FL

 

[sidbrazil]

Thanks for all posts.

Here is the deal:
We are designing a mock-up for confort assessment. Due to commercial and practical aspects, we are using the Buttkicker shaker. What we are looking for is to create an vibro-acoustic atmosphere, and we are not so worried about amplitude precision.
Eventhough, we want to assure a 0,1g-peak of amplitude at least.

The manufactures has no information regarding eletrical to mechanical efficiency, and dynamic capability. Probably what we will do here is a try-out to figure out the best distribution of the shakers...

Anyway, many thanks.

 

[IRstuff]

I finally looked at the description of the shaker in question. It won't do what you are trying to do, since there is no direct coupling of the moving piston to the object being shaken.

If you want to shake something, then you need to get a real shaker.

TTFN

FAQ731-376

 

[GregLocock]

It's just an inertial driver? well, you could still use it to create a known vibration, using a feedback loop.

I bought a similar product for 20 bucks and found that it was compeletely useless when screwed to a chair - all it did was excite the resonances of the chair, ie musically all it had were wolf tones.

Oh well, the power supply and amp were worth 20 bucks.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[FeX32]

Interesting. I never knew that you could get those for your home theater . I looked at the Buttkicker shaker site and it seems that the specs on some of them do state a rated 'weight'.
For example:

http://www.thebuttkicker.com/home_theater/products/bk_mini_lfe.htm

I believe you would need more information if you were to dynamically model the system and calculate the mass of course.

TTFN,

Fe

 

[IRstuff]

Not sure which weight you refer to, but the only one visible is 2 lbs, which is the weight of the shaker itself.

TTFN

FAQ731-376

 

[FeX32]

Yes, you are correct. Sorry about that IRstuff.
Anyhow, if it were me I would just call the company. There is surely someone that would know the allowable mass.

ttyl,

Fe

 

[IRstuff]

If you're going to wrap a control system around it, then you might as well get something designed to do the job correctly:

http://www.dynsolusa.com/edshakers.htm

http://www.dataphysics.com/products/shakerfamily/shakers/index.htm

http://qualmark.com/Products/edShakersModels.html

http://www.lds-group.com/docs/display_product.php?product_item_id=448

TTFN

FAQ731-376

 

[FeX32]

You've got me interested. How would you go about controlling the inertial shaker? And for what reason does it need to be controlled? Thanks.

Fe

 

[GregLocock]

If you want a specific amplitude from it then you need a feedback controller, and a sensor. Steam powered modal analysers such as the HP 3562 (all hail the 3562) would do this for you automatically, on a sine sweep. Some shaker controllers would use spectrum shaping to get the same effect on pseudo-random and so on.

The problem with a chair is that it has a couple of very strong modes (bounce on seat and backlsapping) that are non linear and not particularly well damped. Finding a sensor location that would adequately sense all the modes would be tricky.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[FeX32]

Thanks Greg. I've never seen a HP 3562. I have only used some similar equipment by Brüel & Kjær.

Fe

 

[sidbrazil]

Hi guys,

Thanks again,as Greglocock pointed, the system is very cheap. We will get a shot down here.

The idea is to have some accelerometer on the foot and also at cushion region in order to verify the amount of vibratory level imposed. We will be controlling by a in-house executable programmed in Labview. If we experience an resonance (by our experience they are to 5 Hz the dundamental one) we could change the shape of output signal. We will spend some time here because this will be a open loop control system. It is not worthfull to create a program for closed loop control.

We are confident that in some level it will works. We've seen similar stuff being developed by Vienna University, Volkswagen and Airbus... keep in mind that the desired vibration level in pretty small.

 

[FeX32]

sidbrazil-

If this helps, the supplier indicates a maximum force of 70lbf for the BK-LFE (I believe the inertial mass is 3.5lb). You may be able to use this information.
ttyl,

Fe