Algodoo

This is a very simple clutch, you can use it and alter it if you want, but credit me, and lethalsquirl.

E to engage
D to disengage
Arrow Down to brake the wheel it's driving.

I'm going to have to give credit to lethalsquirl, I saw this phunlet: http://www.algodoo.com/algobox/details.php?id=45895
and thought I could try it with less parts.
I did get it with less parts but it's also a lot less reliable