pic: Custom made, sheet metal Chassis

Custom made chassis from team 3478, plannig to use this chassis at IRI.

What speed is this drivetrain geared for? I didn’t think a two stage ball shifter direct driving a wheel gave enough reduction for 4+ inch wheels.

Are you using a turret punch or a laser cutter to cut out the sides? If turret punch, make sure your tolerances will support this design.

You’re weakening your frame by breaking the upper-inner flanges for gearbox clearance. Instead of two C-shaped pieces of metal, try flipping the upper flange of the inner sheet pieces in the opposite direction, creating an “S bend” on the piece. This allows you vertical room for gearbox clearance while keeping the top flange continuous, which is important for the strength of the chassis.


Yea, I would be careful about this. Even the slowest case it’s going to be on the very fast end of FRC bots, unless there is another reduction hidden in there some how.

You can use this tool to help you:


This year we used a ball shifter plus a 2:1 reduction using the sprockets. We had a low gear of 7fps and a high gear of 16fps.

Edit: You could also try to add a support for the battery as part of your drivetrain, i’ve seen many top teams do this

In general, looks really good!

What thickness sheet metal are you using?

Where and how does the bellypan mount?

What drop are you using?

You might want to do a bit more overlap between the front frame member and the 4 “drive channel” frame members. Looks like you only have 3 holes within 1". Getting even another .5" (or preferably 1") would be great. Your bellypan and material thickness might make this issue less significant though.

I’d recommend having a few standoffs or stiffeners going between the inner and outer plates of your drive channels. A couple of these in strategic locations can go a long way towards reducing stresses at your other joints.


Agreed that this does weaken the frame, but if the belly pan is mounting on each side of the gearbox, the sheet metal thickness isn’t on the low side, and they add a couple drive-channel-stiffeners, I think the way they have it would be fine. That said, I’ve only fabricated one sheet metal drivebase (despite seeing dozens and designing a few). The s-bend can be a neat fix, but can also make accessing the wheels fairly annoying.

Nathan Streeter:
We do have stiffners between the plates, we are also joining the drive plates vertically to the rest of the chassis, this is our first sheet metal chassis so what do you exactly mean by belly pan?
The current drop is 1/8", we are using de blue nitril tread from mc master.

Concerning the gearbox issue, our last robot had it that way (direct drive) but with the 2 cim vex ball shifter, we had no trouble in our drive although we thought it was somewhat slow, thats why we are using it this way with a 3 cim Vex ball shifter

The belly pan the flat piece of metal in the bottom of the chassis that all of your electronics are mounted to.
Please note that it’s not a sheet metal drivetrain feature. Belly pans are on basically every drivetrain (including the old and new KOP drivetrains).