[EricH]

Originally Posted by drakesword

I think treads would be good at traction but not much more.

Incorrect, actually. Treads are often used when the surface that needs to be crossed is marshy, somewhat swampy, unstable, dirty, or sandy, or some combination of those.

The objective is to spread out the weight so that the pressure is less so that you don't sink down into whatever it is you're trying to cross. Think snowshoes--if you're not wearing them, you break through any crust the snow has on it and go knee-, shin-, or ankle-deep until you get to the point at which the snow under your foot will support you. If you're wearing snowshoes, you go much less deep, because there is more snow to take your weight. Tank tracks take the entire weight of the vehicle and spread it out over the length of the vehicle by some width that, for a large military tank, could easily be a yard or two (taking both treads together).

For sand, it may not be as much of an issue, but it's still worth looking at. There's a reason a lot of heavy construction equipment and tanks use treads. An awful lot of small, light military/police-type robots use treads.

Large wheels are also an option, especially if you want car-type steering. Just make sure that they're big enough to let the robot scoot over the top of the sand as much as possible, or that the robot is heavy enough and has enough ground clearance to pack the sand behind it.