In our past robots we’ve used 1/4" perforated PVC sheet, but it’s gotten VERY expensive. I guess we could try 1/8".
What do your teams use?
We use a 1/16in or 1/8in aluminum sheet that we rivet to the bottom 2x1 rails of the robot frame. We normally use VHB tape or water jet holes for electronics mounting.
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I believe the last two years we used 5/16" sheets of 6061 Aluminum, probably will again this year. Is it probably overkill? Yep, but we like the peace of mind and putting more weight down low is never a bad thing.
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Polycarb. Place the left over weight wherever we need to.
Robot collisions won’t be as high speed so we don’t need the extreme stiffness down there which the 1/8” wall already provides.
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We use 1/8" aluminum that we cnc electronic mounting holes and a 1/2" hole pattern into.
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0.08 in 5052 aluminum
Aluminum is my preference, but polycarbonate is also slightly better than PVC in most cases.
This stuff is convenient and fits most chassis designs, including the kitbot – just bandsaw or jigsaw it to size.
Or, if you want aluminum and can’t machine it in-house, CAD it and order from FabWorks or SendCutSend.
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Last year my team used a 1/4” steel bellypan but the material this year will depend on the weight of the rest of the robot.
qty: 3
1/4in steel, stacked. No “speed holes” or ribbing/patterning. Powder–coated. No electronics or device mounting holes/features, just ballast. 17lbs-ish each?
Low CG? 
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We tend to 1/8” aluminum, but for test robots we’ve been using 5mm floor underlayment (plywood) as it is dirt cheap and easy to work with. Last year we built our comp robot with it and changed out to aluminum just before our first comp.
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I also support this method, especially if you have a laser cutter; we did it in 2023 and 2024. It’s pretty wild when all of the electronics are hanging there during the change, but it’s a great implementation of rapid prototyping and fail-faster.
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Wish we had one. But, just a few minutes with a jig saw and a drill and we’re good to go.
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How heavy was that?!
11 ga. 4130 from our 2024 chassis (until we need to lose some weight). We’ve got 2 regionals and an offseason on this monstrosity with no visible deformation in the frame rails that were previously attached.
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~30lbs with pocketing on one side and a 6 inch hole on the other
For the most recent bot we used a 1/4" aluminum plate and this is likely going to become the standard. In the past we also used 2 1/8" aluminum plates plus 1/8" of polycarbonate (mostly decorative), iirc one of the aluminum plates was originally going to be steel.
Recently we’ve talked about trying out a brainpan and adjusting our chassis structure but the belly pan will likely remain 1/4" aluminum.
Although we have not done this, one moderately common approach I see around is having less belly pan and more trusses. Having some 2"x1" bars span across your chassis means you can pocket out a 1/4" or 1/8" belly pan quite a bit. Of course this has pros and cons but it seems to have worked great for a lot of teams.
On a side note, we did use about 2.25" of MDF once on a off-season bot and it worked quite well.
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In the past we’ve used 6mm polycarbonate sheet that has been routed on the CNC router. This year we’ll probably look for something a little more substantial to reduce our center of gravity.
1/8in 6061 aluminum. usually solid pan. depending on height of the robot, we have considered steel as a material as well provided we can still meet our weight targets. We really dont like tippy robots so we push the CoM as low as possible
We have been using 1/4" aluminum, however we might switch to 1/4" or 1/8" steel this year for a lower COG.
This is pretty much what we did last season, but we didn’t swap it out for competition. It held up shockingly well and made mounting really straightforward, especially since we didn’t need the belly pan to provide any structural support to the robot since we got all of that from the frame anyways.
We started out with a fully wood belly pan originally and went through two regionals like that. After our second regional though, the wood where our battery was supported was getting really messed up due to the extra weight. We then machined a new aluminum belly pan in two pieces, 2/3 covered the area where most electronics were mounted that was still holding up well, 1/3 for the area where the battery was. We only ended up replacing the 1/3 area for Worlds and ran into no issues with the 2/3 that remained wood and even after the hard defense on Einstein it was still holding up really well and was still well-fastened to the robot with little damage to the wood except a few small areas along the edge.
We did end up replacing the second 2/3 this fall before Beach Blitz, but honestly we were still debating if that was even necessary and realistically probably could’ve gotten away without replacing it. So for a robot that is sufficiently rigid on a flat field, I think it’s definitely a great option due to how easy it makes mounting.
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