Looks good. “What’s odd?” Hmm…not sure…other than it looks like it wont be used to power your drive base (unless it’s for some type of crab wheel moving). The 2 sprockets look like they will be driving a chain going out opposite directions of the gearbox. We thought of doing the same thing early in the build period, but instead of making the gearbox we were going to purchase some through a company.
Looks good.
/me goes back to typing his chemistry formal lab report 
Is heavy, really heavy…answer to the odd question.
C’mon it’s easy. In the bottom left side of the gear/sprocket box there is a bore for a bearing but there isn’t one and that shaft doesn’t go all the way across.