[MrForbes]

I like the idea of using parts you already have. But sometimes the parts are just not right enough for the job.

A concern for a robot like this is control. I'd try to err on the side of too slow of operating speed, rather than too fast. That means you might have to get creative with transmissions, to get enough reduction. The sand environment is tough on chains and toothed belts. I dont know if the AM planetary gearbox is sealed well enough, but I expect you could add a dust seal over the output shaft if needed.

We have used V belts for reduction and making a "forgiving" drive system for mechanisms on our FRC robots, you might look into them. Around here it's easy to get large and small pulleys, as they fit the very common evaporative coolers we use in the summer.

btw if you look at the garden cart....it could have the wheelbase and track width modified, and you might be able to use the steering system. They turn very sharp.