pic: 25lb Drivetrain

[GeeTwo]

I do like the concept, and the weight economy! It's designs like this that make me want the team to invest in a sheet metal brake, probably even ahead of a lathe. If we just had the space for some real shop machines (32'x24' for storage and workshop and programming and maybe everything else).

While c-channel is not as strong as tube (especially in torsion, and significantly in around the axis perpendicular to the "missing" face), I do not see this as a showstopper - as previously noted, the 2014-2016 kit bots used folded c-channel to rave reviews. (3946 purchased some 2015 frames on closeout that we plan to use in 2017, or in 2018 on the low-percentage chance that we decide to go another route.)

There is plenty of room for attachment points. The top of the front and rear rails, and the portions of the tube which do not have chain behind them can be perforated as needed.

I understand that chain-in-tube is usually "set it and forget it" over the course of an FRC season, but with the capped tube ends, this design does not seem to have a good way to swap out the chains if disaster should strike. As a first mitigation, I would probably NOT perforate the drive tube for mount points, but rather mount a c-channel or thick-wall tube of versa-frame in a location which would allow a side tube, wheels, chains, gearbox, and motors to be removed as a single unit without removing anything else but the bumpers, or design "everything but" the drive chassis and things mounted to the belly pan to be easily removable to allow drive rail removal and repair.

Finally, This was not a design point, but someone brought it up: I don't see how this could work as a kit frame. Kits usually ship in a box roughly 36" x 8" x 8", but this belly pan unit would have to ship as something rather larger. Even more critically, there is no good way to make this so that a team can select "long/square/wide" using a band saw. (And OBTW, the kitbots since at least 2012 have a LOT more options than are listed in the manual, if you are willing to put in a bit of skull work.) If you skipped the belly pan, much more is possible, but that misses the key feature that makes this such a weight saver.