pic: 25lb Drivetrain

[Chris is me]

Putting bearings straight into 1/8" wall tubing is just fine, it's only 1/16" wall tubing you really have to worry about ovalizing with. You should be fine there.

I'd consider riveting the bearings in instead of screws, just because I hate 4/40 screws and breaking taps and stuff. I guess if you have to change out a bearing there will be some rivet scraps inside your tube and that's kind of nasty.

Originally Posted by bkahl

A cross section of a C is almost negligibly weaker than a box. In this scenario, a single piece belly ban and front and back members is actually extremely rigid.

On top of that, a single-piece bumper could add even more strength.

By your logic, would not all drives with a similar single-piece belly pan and cross-members be weak, and limited in mounting? IIRC 971 uses a similar style design. What about the kit frame? It uses C-channel cross-members too.

I agree that the one piece belly pan / C-channel member will make this chassis likely rigid enough to perform well, particularly with stuff on top of it, but I wouldn't say a C-channel is "negligibly weaker" than tubing. It's certainly got substantially less resistance to bending. In this case, it's somewhat offset by the fact that it's got a giant bottom flange connecting it to the other side, and that the C-channel hugs the inside of the drive tube. This style of drive has certainly been battle-tested before.

I think this drive would get some strength benefit from making the top flange longer. Just an inch long is a little wimpy as a C-channel, and it could kink in the middle if hit really hard (and the bumpers aren't backed up with their own frame etc). I would just extend the whole flange to the length that is present at the points where it attaches to the frame. You're already using that material anyway; what's another few ounces per side to resist bending on impact a bit better. Especially if the belly pan is .090.