While I still think that this is a field element, if it IS a robot piece...my vote goes to battery mount. Doesn't it just look like a battery would fit in there nicely?
Though the reason that I don't think that it's a robot part is because of the pins/bolts/?? at the ends of the two tubes. No matter where this assembly would attach, it would be VERY constricting in terms of robot design. I understand that the rover wheels last year changed drive trains a lot, but most teams were able to simply modify whatever they had previously used to encompass a differently sized wheel. If this part is to scale by Inventor standards, it seems like it would HIGHLY constrict robot design - even if you found a different way to attach it to your robot/were allowed to do so.
I'm not trying to shut down any ideas; just my $0.02