[MrForbes]

If you have the wherewithal to design and build your own transmissions (and still make the rest of the robot effective), then go for it! If you don't, but you do have the money to buy aftermarket transmissions, then that might be the best way to go. Otherwise make the best of the kit transmissions...but you might have to design around them, as they generally are a low cost design that will just meet the need.

A single speed gearbox is a transmission, and a multi-speed gearbox is a transmission too.