Has anyone come up with a drive/gearbox where the cims are oriented on the same axis as the chassis sides so they don’t protrude into the middle of the chassis?
Bruce
We did a bit of playing with these garage door opener gears
and made a gearbox out of 2x3" steel rectangular tubing that supported the gears and a CIM. I did not get any pictures of it, unfortunately. It was for a winch, not a drive system, but it might work?
Back when drill motors were the drive motors of choice, a lot of teams used worm gear systems to couple the motor to the wheel. The ones I have seen put the motor shaft in the fore/aft robot direction; some could have been oriented vertically.
This made motor bias a non-problem, either incidentally or by design, as the motors would both be turning in the same direction when the robot was moving straight.
In the past when we used to get the drill motors in the kit, team 108 has used bevel gears to make our drivetrain. Even though it worked well, due to the inefficiency, we will probably never do it again.
Worm gears are generally low efficiency. I know 1425 used some high efficiency 4 lead worm gears in 07.
75 used a shaft and bevel gear setup in 07 as well.
Of the two I liked 1425’s setup better, but the space advantage really wasn’t a big deal. Hasn’t been a year yet where you needed the entire center to be empty.
Putting the gearbox over the chassis rails, like 330 in 07/08, might be a better space savings for you.
Back in '96 “hexcalibur” used miter gears direct from the drill transmissions to their drive axles.
The robot used to be at the FIRST Place in NH.
I couldn’t find any pictures.
It was a seriously sweet machine. 
Try to find some pictures of 1075 from the offseason 2006 thru offseason 2008 era. We had a tank drive setup that placed the CIMs inside the belt. they drove a shaft running the length of the belt, and through a AM shifter, into a bevel gear, driving a chain into the cog that drove the belts. If you can find pictures from Kettering Kickoff 2007 or 2008, you’ll have the best chance of seeing how we did it.
Late in the 08 offseason (for brunswick eruption), we switched to a 6wd drop center built on the same platform (ie. any of our 06-08 bots could interchange drive units.) For 09 we built a 2+2 swerve, with 4 modes, and for 2010, we built DS Swerve (FRC’s first, and only, to my knowledge, invertable swerve drive [photo here: http://www.chiefdelphi.com/media/photos/35499]).
In 2003 team 95 used worm gears with the CIM motors and some 45deg helical gears with Bosch drill motors in our swerve drive. The helical gears were pretty okay, the worm gears were awfully inefficient.
To do it again I would use bevel gears, though we’ve never had a space issue with a conventional tank style drive.