## Oscillation and Randomization

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feedme
Posts: 170
Joined: Sat Jan 30, 2010 3:59 am UTC

### Oscillation and Randomization

I've got this project in my computer aided engineering class where we're supposed to design a tennis ball machine on top of a 5 foot tripod. It's supposed to be able to randomly aim the ball and cover the entire court. Being a mechanical engineering student the problem suggests we use a motor driven four bar linkage for simplicity.

While looking up various types of tennis ball machines and such, I came across a brand called Lobster that advertises "triple oscillation" which produces a random shot pattern. I know those machines are more electronic but I was wondering if there was any way to have something be random while still mechanical?

Any other ideas would be helpful also!

BlackSails
Posts: 5315
Joined: Thu Dec 20, 2007 5:48 am UTC

### Re: Oscillation and Randomization

Have some sort of mechanism that is very, very close to slipping, so sometimes it slips a small amount?

Qaanol
The Cheshirest Catamount
Posts: 3062
Joined: Sat May 09, 2009 11:55 pm UTC

### Re: Oscillation and Randomization

Having two axes of rotation which are periodic with irrationally-related periods will never repeat a direction. Add in a periodic ball velocity irrationally-related to the others and you might have enough complexity to pass for randomness.
wee free kings

D.B.
Posts: 197
Joined: Wed Sep 09, 2009 3:08 pm UTC

### Re: Oscillation and Randomization

You might be able to get something chaotic (e.g. like a double pendulum or swinging atwood's machine). That way although the motion itself is deterministic, small changes in your initial conditions (which we might be able to argue are essentially random) will quickly magnify and the overall impression wil be one of randomness. How exactly you could go about implementing this I've no clue...

Slightly less seriously, one could implement a mechanical turing machine and have it compute a hash function.

See also the chronophage for inspiration, which uses "a countwheel with semi random spacing" to make it appear to blink at irregular intervals.