Foot step simulator

[HarveyH42]

Anybody have any ideas on how to build a device that simulates the vibrations made when walking/running?

I'll need a transducer or some other mechanical device able to create the vibrations (maybe 1-5 Hz), lower than subwoofer frequencies.

Need a circuit to ramp the amplitude, so it starts low and increases over several seconds. This should make seem like the vibrations are approaching, getting closer.

And maybe vary the frequency, like walking faster, or running.

The only device remotely simlar to the needed transducer I've ever read about, was pneumatic oscilator, used by Nikola Tesla in his earthquake experiments (mechanical resonance). But the details were always vague, for obvious reasons... Hopefully, this won't be operating anywhere near those frequencies or power output. Don't think an earthquake is possiable in Florida, maybe open a sinkhole...
So, any suggestions on a ultra low frequency transducer is appreciated.

The ramp circuit, can probably pull off the timing capacitor in a low freqency 555 timer circuit. Should be simple enough. Maybe I can tie the frequency and amplitude together (higher frequency and louder output).

 

[RadioRon]

My first thought was to go strictly mechanical since you can get a lot of mechanical vibration out of a small motor with an offcenter arm attached to its shaft. Variable frequency is easy using a speed control (like in a simple battery operated drill), but I kinda got hung up on the variable amplitude part. Hmmmm, need more coffee for this one....