Alt Bike Culture - how does it work?

i wonder about the how does beer bike work ? How they can transport that energy to back whells. I think its a really funny alt bike. I really want to know about its shaft and gear system. If you know something please share . :notamused:

http://www.youtube.com/watch?v=MkulQvz-efw

Looks like it's based on a rear wheel drive automotive platform. Probably has spockets on the drive shaft. Very cool clip, thanks!

But what kind of sprockets? Because the pedals are opposite and how can you make the shaft to turn in one way?

I believe they have two shafts

Yes, two shafts, and a differential.

is it possible to connect two shafts to one differential? actually i watched some different videos about beerbike and i think there must be one shaft and a complex sprockets system. im some confused about it :S because if you have two shaft that turning to different ways is it possible to work differential to one way? it seems like a basic physics problem but in practice its not so much easy to do.

Also thanks for your replies. They lightened me someway :)

Looks like it's belt drive,so 1 belt runs correctly the other belt has a twist in it to make it run backwards.I can't tell if it has jackshafts or not,doesn't look like it,they may be running the belt directly against the driveshaft.