I was around when they built one of these on Junkyard Wars. (It failed in part because of a bum hydraulic pump.) Using rubber isn’t going to work because all that friction is counter to how these things work. (With higher friction rubber in order to get it to turn you’d need a ton more power all going into fighting the other spirals motion, tearing off your drive spiral, and straining your drive/suspension, non of it going into driving your device forward.)

The trick is to make the whole spiral as smooth and sleek as possible so there’s not much friction against the rotation, and more of the power goes into the forward/back drive. If you have too much friction you can rev and rev all you want to but you never go anywhere.

Take care choosing your pitch/spiral height to work with the target material. (the playa) More aggressive pitch means more stress on the drive train and spiral. If the spiral is too high (tall) it’ll be unable to turn in the playa and will tear itself off. Trying to make it work on lots of different materials is going to be much much harder then trying to tune for just one.

A cab is good because if the a spiral starts to come off it flogs the passengers. :] (I guess you can choose a rotation direction where it flogs the undercarriage instead for forward motion.)

For playa I wouldn’t choose a single perpendicular spiral strip. (too easy to bend/tear off) Much better to use an inverted V shape (or even maybe a 90 deg V) so both legs are welded down. For Playa you won’t need a lot of penetration, so you might even just be able to use stock small sized angle iron.

Sorry I’m just thinking out loud. blah blah blah.

Good luck with this project. I loved the Snail Car, and I can’t wait to see this come to life!

-Kurt

Alliance, NE