Eh Pike,
Just a thought for your tank mate, to improve the grip a heap better replace the chain with a toothed belt say off a car engine. It's easy to cut and join by splicing and contact cement seems to hold up pretty well. After looking at the tank I'm inspired enough to make 1 for me and my son. I do have a 7 channel R/C controller off an R/c plane so hopefully I won't have alot of trouble interfacing it. Then once I learn pic's a bit more replace the R/C controller and make it automonous.
Unless the laws are different in Australia?, it's an offence to use an airplane R/C for a model other than an aircraft - for very good sensible reasons!.
local scrap yard has the right stuff when you come at the right time and at dirt cheap prices. I got 7.5 kgs of aluminium for $13 US (15lbs) but you have to come at the right time or they'll send it off to a great big smelter.
i was considering a composite rubber/steel bolts tread system but i ran out of time and just took the easy way out with press fit cogs, and bikes chains. I'll draw a diagram soon so you know what i mean.