pic: 25lb Drivetrain

[bkahl]

Originally Posted by Sperkowsky

By removing the crossmember 2x1s in favor of the bent sheet metal you are saving a bit of weight. But it is not as strong and you are more limited in mounting points. The few pounds its saves is just not worth it imo.

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.

EDIT:

Originally Posted by cad321

Is there a reason you chose not to use bearing blocks on your drive wheels? Although I haven't built a WCD before, my understanding is that their benefits far outweigh the cons (the only con in this I could see is possibly weight as you're limiting it to 25lbs).

Another reason for this design may be for maintenance.

With the one-piece belly pan and members design, you "cap" the end of your drive tubes, making it hard to change a chain in an (unlikely) emergency. Being able to pull bearings from the tube may allow you to slide a chain in without taking the belly pan off (even though it still sounds like a nightmare).

[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.

[Ty Tremblay]

I wouldn't even bother with holding the bearings in the tube. If you used screws and washers on the ends of the axles (or properly toleranced snap ring grooves) the bearings will have no where to go any way. 319 tapped the ends of our thunderhex shafts 1/4-20 and ran them all season without issues.

[JesseK]

The bellypan design is quite interesting. If it were the basis for a kitbot, it would turn the kitbot frame into a 7-piece rivet operation.
It's like the AMU chassis found a way to become WCD.