Swerve Chassis Question - Belly pan

We are new to swerve and have a few questions:

  1. Should the belly pan be an integral part of the frame (ie bolts to the underside of the frame rails), or can it be a pan that sits on a shelf inside the frame?

  2. What do most people make the belly pan out of? Aluminum? Polycarb? Plywood?

  3. Should the swerve chassis have a 2x1 support running across the middle of the frame?

I’ll help here:

  1. You will ideally want it as an integral part of the frame.

  2. We prefer aluminum and you can reference what the poofs do but Wood and polycarb work great as well! Baltic birch has been my choice for offseason robots.

  3. You don’t need to, but depending on mechanisms it may be a great point to mount elevators and arms to.

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We have some 3mm plywood we use for a laser. Would something like that be too thin for a belly pan?

I’d recommend using thicker wood for the bellypan, more like the 3/4" stuff you use for the bumpers.

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We use 3 mm stuff for ours, but requires additional supports if you want it to span the entire chassis.

It starts to flex over the entire span

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Would probably aim for 6-9mm or .25" - .375" thick wood.


Yes, BECAUSE you need good frame stiffness (which is where you were going with the 2x1 question) bellypan is probably the lightest way to go about this. Ideally you want 1/4 of the robot weight (assuming 4 modules) on each wheel. Flex in the frame matters in this sense.

With careful work you can integrate stiffness into the super structure… But bellypan is easier.

So would you recommend the thicker plywood and the middle brace or something different?

Plywood is a great material, 3mm may be a little thin, but that is a gut feeling. It is probably okay, I wouldn’t be scared, but 3/8 is probably a better call overall (bolted into the shelf)

It is cost effective, easy to modify/iterate… Only “problem” is it is a relatively light material down low. “Health mass” down low is important, the bellypan is a great place to splurge.

We don’t have any sheet aluminum or thicker polycarbonate so we are limited to plywood at this point.

I think we have some .25" and .5" plywood, so we can use that.

Would you do the brace as well?
Also, do most teams just bolt the pan to the frame with through bolts or nut certs, or pop rivets?

.5 plywood would be great.

A dozen fasteners around the frame perimeter (probably threaded so you can assure similar torque) with ny-lock nuts and washers is probably sufficient.

If you want a brace I would put a piece of angle aluminum or 1x1 bolted in a few places to increase stiffness. 2x1 is overkill.

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1/4" is enough for sure, that’s what 1072 did in 2020. However to get more weight down low on the robot 1/2" is good.

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3/8 AL bellypan. Just cause.


Baltic birch has been my choice for #1 seeding championships robots.

But also for offseason robots.


This is only 27lbs on a 28x26 robot. Unironically, I would consider it. 1/8" steel could also work if you can drill it, for the same weight.

You seem pretty familiar with swerve. We are just starting. Is it possible to configure the swerve chassis in a rectangle or does it have to be in a square orientation?

Remember the thicker the bellypan the lower the ground clearance.

Easily done in a rectangle. There is nothing mechanically causing an issue with this. There will of course be less stability in one direction. a lot of default code assumes square, so you will need to look into that.