Simulation of force produced by a falling mass

[Pina87]

Hi.
Does anyone have any suggestions how to simulate the force produced by a mass of 2,5 kg (max) falling from a hight of 20cm (max) into someones hands. We want to make some measurements in which we want to be able to change the amplitude of the force. The measurements would be held for 30 repetitions with a 2-5 second pause betwen. It is very important that we can simulate the impulse.

I was thinking about solenoids but I am affraid that it could come to overheating. Or not?

Any suggestions?

 

[TheTick]

Force exerted depends on the amount of distance taken to absorb the kinetic energy. A soft cushion will absorb the energy over greater distance than a hard surface. This does not include energy dissipated by deforming or breaking the falling object or the landing surface.

 

[IRstuff]

The expected terminal velocity is about 2 m/s. I would comtemplate something like what Mythbusters often uses, which is a swing arm powered by an actuator, either electrical or pneumatic. You'd need to instrument it to verify speed, and ensure that the hitting end is shaped to match the size and stiffness of the "mass."

A low-mass swing arm with an actual 2.5kg mass would seem preferrable to me. There's a lot of dynamics that have to be duplicated to make any simulation match the actual reality.

Are you testing the hand or the object? If it's the object, there's much less to do to get verisimilitude.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Cockroach]

Yes, TheTick is correct. You essentially treat the problem as a change in impulse, which is work departed to the surrounding environment from change in velocity. That work is essentially force time the distance to stop that body from downward motion.

You could get this from inelastic collision theory since you assume no mass loss or gain to that body and simply a change in direction, velocity variance.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[zekeman]

Mdv/dt=F
Fdt=d)mv) and integrating you get
impulse=change of momentum

As the Tick implies you can get various F vs t values depending on the stopping mechanism.

Not sure what you are after but an accelerometer with a readout can get you that force-time history.The area under that curve is the change of momentum (mv) but in general you can't get a constant force over time.

I would start with wooden stops of various stiffness for the stop test.

 

[Pina87]

IRstuff: can you please paste a link of the swing arm, because I only get motorcycle swing arm in Google .

I'm also very limited with the space the simulator should take. We tought to put it in a box of 30x30x30cm.

Thnx for everything

 

[MiketheEngineer]

This has been discussed probably a 100 times in these forums - Search them

Basically; F=ma

Once you figure a - or de-acceleration which is based on distance and time or delta l/delta t - you got it.

That is the detail where the devil lives.....

Why do you thin Ford & Chevy and BMW, etc spend thousands of dollars crashing cars every year.

If they knew those numbers - they wouldn't wwater their time and money.

I have found that a few ACTUAL test will teach you a lot..

 

[IRstuff]

Just imagine a ballistic pendulum rotated 90°. If you're really cramped for space, you should consider a scaled-down version of

http://hmtbj.com/eng/products_shock_series.html

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize