pic: Chameleon Drive

[JesseK]

"Chameleon Drive" implies the thing blends into the background ... yet I totally see all of that drive in all configurations o.O
(Ok, I kid...)

The most basic piece of this 'drive' is the H-frame. Your H-frame setup is very verstatile. However, I don't think the gearbox configurations are. For the 8WD and 6WD tank variants, why not just use the CIMple boxes that come in the KOP? The chain runs are easily tensioned by sliding the transmission, it's lighter overall, c.g. is lower overall, and the sprocket reductions are adjustable so you aren't stuck with purchasing ~$100 in gears just to get the right speed for a given year.

For the slide drive (your bottom pic), you may find that the robot doesn't need to slide sideways as fast as it moves forward/back. If this is what you find, you may be able to use 2 RS-550's (properly geared...) in lieu of 2 CIMs, thereby putting the 2 CIMs back on the outer wheels for better power characteristics during normal play.