I messaged Greg yesterday asking him some questions about his large tank drone and he was kind enough to answer in some detail. He does have a discussion at this link regarding his questions on APM. I don't want to distract from that so as he suggested I have started a new discussion to continue the leeching of information about his drone and related engineering questions.
Here is his response to my first couple questions:
First is, how much load and how rugged do you want your drone to be? We did 6 wheels so that it could do very rugged terrain and carry heavy loads (500lbs) stablely. And low tire pressure could act as suspension (so we wouldn't have to put shocks on it). It is also meant to be a vehicle (you can ride it). You may not need that. This class of machine and motor can draw 150-200amps at times, sabertooth can't handle that. You need industrial motor controller (we use Curtis, I can look up the models for you) one for each motor. Also, I think CAN bus is more reliable and a better control system than resistive throttle.
(Also, with drone this size, you got to think about safety. Mine is 350lbs and can go 20-30mph. Fully loaded it is a small car. So I like a LOT of failsafety on it. )
All in all, we had to move into the industrial realm...the hobbyist/DIY stuff doesn't really cover this much power. This is more a vehicle than anything else. The motor controllers on this (if the company will even sell them to you) are normally used to operate fork lifts.
4 wheels is good if you don't need to carry a ton through rugged terrain. Our next version we expect to be smaller 4 wheels. Still skid steer. That one maybe you can use a sabertooth for and smaller motors.
Meanwhile, I am going to get my colleague to join the forum; Dave (works with me) is an engineer and machinist, and he did all the gearing on that drone...he is a kind of gear expert (used to be head engineer for a Formula One team) I am programming/electronics mostly, and dave is the classic engineer. We did that drone together.
I think I can most the CAD drawings for it. Maybe make it an opensource hardware platform that we can all improve on. Branch into a 4 wheel version also?
I will get some pictures, designs, motor options, motor controller types and battery suggestions.