I have an old 1988 catapillar 426 backhoe, 4x4. It weighs about 16000lbs, but is not really *that* big. I don't use it for anything anymore, and so I was wondering if it might be an interesting to convert it into a robot. Perhaps just remote control, but maybe have macros built in so it could perform repetive operations like digging a trench. Since I already have the major component (the working backhoe), I am thinking maybe it would not be too expensive to automate it? Air cylinders to actuate the brakes (they are somewhat mechanical....the foot pedals control a complex linkage to the rear differential, which contains a wet plate brake thing). The brakes actually do not work that well anyway :-). Steering could be as simple as a large gearmotor or something. The expensive part would be replacing the hydraulic spool valves with solinoid valves...that could run many $$$.
I have about 21 acres of very interesting mountain land to play on. I could be part of that exclusive club of 16000lb robotic backhoe owners...
Rick