Los Angeles designer needs local help

[lineofdraw]

I am an independent designer with a degree in art/illustration, not mechanical engineering. I am working on a project that requires 2 geneva wheels. One Geneva is 4 stop, the other is 3 stop.
Ive made a couple of genevas utilizing illustrations in books and a laser cutter cutting 1/8" delrin but the resulting wheels do not function perfectly.
My deadline is looming and I need perfect intermitant motion... can anyone help?

 

[ivymike]

have you already had a look at this article?

http://en.wikipedia.org/wiki/Geneva_wheel

 

[CorBlimeyLimey]

What do you mean by "perfect intermittent" motion?

This article may help;

http://www.me.berkeley.edu/~adarsh/Geneva.pdf

 

[MikeHalloran]

It's theoretically impossible to get perfect intermittent motion from the classical Geneva wheel because of the shock associated with the roller banging the slot. Many variants exist, or once existed, to deal with the problem, which remains.

It used to be possible to buy pocket-size 'precision' Geneva pairs from outfits like Secs and Berg and Pic and maybe half a dozen other 'precision' mechanical device suppliers.

I'm guessing that your mechanism is too large for them to do you any good, even if you could find them, though you gave little hint of scale or mass.

If your prime mover is electrical, it _is_ possible to get 'perfect' intermittent motion, or nearly any arbitrary motion, from a programmable (electric motor) drive... which is what I'd be inclined to use instead of a Geneva drive these days.

If all you need is better precision than a laser cutter can give you, a CNC mill can give you better edges, possibly starting with the same G-code.









Mike Halloran
Pembroke Pines, FL, USA

 

[lineofdraw]

Thanks for all the good information. I am really little better than a layman. Formulas and math go right over my head.
I am great at copying. I have had no luck finding quality images of a three stop geneva wheel.

Can anyone point me in the right direction?

 

[hydtools]

Here ya go.

http://www.tangendrives.com/seriesr.html

Ted

 

[EngineerTex]

Here's a three-stop cam that I drew up in a few minutes. You said that you can copy, so I hope that the geometry in here will be enough to get you going.

The geometry is pretty straightforward. If you need info on how to derive this, I could probably derive it and post it if you want.

Good luck.

-T

Engineering is not the science behind building things. It is the science behind not building things.

 

[unclesyd]

Here is EngineerTex's drawing in action.

http://mw.concord.org/modeler1.3/mirror/mechanics/genevadrive3arm.html

Look at the Molecular Modeler software and the additional models available.

 

[Compositepro]

There are many companies that make these mechanisms so it seems wise to get one off-the-shelf. I disagree that there is any banging involved is a properly made unit. The motions are modified sine and there are no discontinuities in the acceleration curves.