[Aren Siekmeier]

If you're going the custom route, why not make them even smaller, say 3 inches? Obviously you can't get much smaller for it to be driven really at all, but decreasing the footprint makes room for other stuff. Although 4 inches is probably good enough and it already looks to be a tough scale for some of the finer details.

I would agree that these are Heavy Duty. I wouldn't know, but those nice fat mounting tabs don't look ready to bend any time soon, particularly in comparison to AndyMark's sheet metal versions. It definitely comes at the cost of manufacturing ease, though.

You should definitely pursue this as a way to explore your team's abilities and gain experience with the detailed manufacturing process. However, in general, I don't really see a competitive advantage to these things, when four 4" omnis at 90º to each other offers the exact same functionality with approximately the same footprint, far less loss due to the rollers, and much simpler (and cheaper) wheels.