# Clever Guys -- Here's one

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Because they are my competitor

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A good question. ;)

Amax = omega^2 * Xmax, where Xmax = peak height of sinusoidal oscillation and omega is angular frequency (radians per second).

8"p-p = 4" peak = 10.16cm, 30Hz = 30 circles per second = 30*2pi rad/s. Max acceleration is thus 36,576m/s^2, which yanking on a mere 454g (1lb) will produce a peak force of 16.8kN, around 1.7 metric tonnes. Hope you have a strong and light crankshaft!

For reference, a force of 10kN applied to a 1kg mass (2.2lbs) for 1/60th of a second (one half cycle at 30Hz) will accelerate it to a velocity of

167m/s, which if directed vertically will shoot it 1,417 meters in the air (about half a mile), I think. ;-)

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

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You slipped a decimal point. The acceleration would be

368g's, not 3680. That's for pure harmonic motion, for a slider crank with the rod 2x the length of the crank throw, 16" in this case, the max accel will be approx 25% higher.

Ned Simmons

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That's what I use : )

The pump flow requirement for 4 inches at 30 Hz is quite large, as you would expect.

For small displacements the sevo valve usually limits the frequency response

You can also run resonant dwell, but still nowhere near 4 inches

As someone esle pointed out, about 368 g's

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If you wanna have some fun, run in displacement mode and vary the frequency until the floor starts shaking...

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[snip]

He'd need A/D for the input pots. I was thinking you could use PWM instead of D/A for the speed control, but then perhaps hydraulic valves don't like that kind of treatment :)

Tim

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Pots would work, up/down buttons would work, what specifically came to mind was a couple of rotary encoders with knobs. There are some inexpensive ones out there now.

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If you do it with a crank and connecting rod, the motion is not quite sinusoidal. If the connecting rod is n times as long as the radius of the crank, the error, E, in percent is n 2 4 6 8 10 E 27 13 8 6 5 Note that as n gets bigger, the error gets smaller and converges on

100/(2*n)%.

Ted

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: A Sybian maybe? --Yeah, but he wants to use a 3 hp motor; must be for an elephant! :-)

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On Thu, 05 Aug 2004 03:09:55 GMT, RoyJ calmly ranted:

I'll bet they used more than a 3hp motor on that'un, wot?

- - - Brain cells come and brain cells go, but fat cells live forever. ---