What are the Pro’s and Con’s of a belly pan.
I notice most are made out of sheetmetal but would lexan make a good sub?
On 973 we like to run 6mm high quality Baltic Birch as the bellypan.
Very fitting for your team name.
We used Baltic birch in 2016 and it was great. I accidentally bought a lower quality sheet for 2017 and it was hard to work with and looked horrible. Look for the quality stuff.
Teams that used non-pocketed aluminum bellypans, what thickness and grade do you use?
Either .09" or .125"
We’ve made ours out of lexan many times and it’s worked well. It really started for us back with the cRio, since making it out of Lexan let it double as a non-conductive electrical board.
Belly pans add a lot of rigidity to your frame, making it more robust. It also can help keep field debris (and occasionally game pieces) out of your robot, and many teams use the space to mount electronics.
They definitely don’t have to be metal. Apex Robotics 5803 has used 1/8" polycarbonate for a belly pan every year so far. As Adam mentioned above, Birch is also a common option.
A non-pocketed 28" x 28" x .125" AL belly pan weighs 9.5 lbs. Great if you want ballast, but you can cut away 3/4 of the material and still be plenty stiff.
Belly Pans are really great at a lot of things:
- Simple electronics mounting
- Structural stability of the frame (cross-bracing)
- Protection of components on or above the belly pan
- Tie down locations for wiring
The drawbacks from my perspective are few:
- Possible added weight
- Lower ground clearance
- Difficult to access things from under the bot
I am sure there are others I am missing, but those are the most glaring to me.
As Adam said, wood works great, and a lot of teams use plexi, sheet metal, and various other materials. Many teams CNC lightening patterns with mounting holes already laid out so all they have to do is bolt the electronics down without even drilling. If you aren’t close to the weight limit a regular piece of thin (14 Ga ish) sheet aluminum is perfectly acceptable. Perforated materials seem to work well for a lot of teams as well.
Do you know the weight of a 254 style pocketed bellypan for comparison?
Whether you need a belly pan and how much depends on the rest of your construction.
The belly pan serves the structural function of helping keep your chassis square, essentially serving as a super-sized gusset. The harder you’re hitting things, the more likely you are to need it.
The belly pan serves the secondary functions of keeping things on the carpet and field coming up into your mechanisms (critical for STRONGHOLD as an example), and as a base for hardware (commonly controls).
The only cons I see are that it does take some resources (dollars, time, weight), and that it serves to keep things on the carpet coming up into your mechanisms, which may be desired for some pickups.
What we did the last three years and why:
- We skipped a belly pan completely for 2015 because it wasn’t needed.
- In 2016, we used 1/8" unpocketed aluminum to survive hard hits and rough terrain. (We probably would have used birch if not for a head coach with a “no wood after rookie year” rule.)
- We also skipped it in 2017, having cut a KoP chassis almost in half and planning an inside-the-chassis gear pickup.
Depending on area and how extreme the pocketing is, 2-4 lbs.
Where do you buy your plywood from?
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Ours is 0.09" thick. It weighs about 3 lb., and has cut-outs for gearboxes, tool access to encoders and shift cylinders, and inboard rear wheels.
Made of 6mm Baltic Birch, it would have been about one pound lighter.
My team has used Lexan belly pans the last couple of years. They worked very well, but the way we attached the first belly pan that we did put the lexan on some strain since we never heated it when we bent it, and in a post season competition it shattered(we were all suprised) into pieces while we were crossing a defense. However everything that the bellypan was there to protect was safe, and we had no problems this past year. We also didn’t mount anything directly to the belly pan, and I don’t think lexan would work as well in that aspect as other materials.
Do you guys mount the plywood with rivets? or some other method?
We went 1/16" alu once without pockets because it was what we had laying around. It held up fine even in a rough game. By the end of the season it had some nasty dents but overall it did it’s job. Would do it again if pocketing wasn’t a option.
We used perforated PVC last year, worked fine.
The Milkenknights have also started to use a 6mm Baltic Birch bellypan (thanks Adam). It’s plenty light, and now with out laser cutter Bellypan machining time went from 10+ hrs (routing lightened 1/8 aluminum bellypan) to ~30 minutes (routed wood bellypan) to under 5 minutes (lasercut wood bellypan). Because we’re making all of our stuff in house, that time difference is HUGE and clears up machines for other priorities. We mount with 3/16 rivets across our 1" hole pattern and have no issues with wood on our bellypan across 2 seasons and 5 robots.
Unless a sponsor is making your bellypan or you have above average machine access, I’d recommend using baltic birch or another similar material that doesn’t need to be lightened to really speed up your manufacturing process and free up machines for other jobs.
Are you sure it wasn’t acrylic or PVC or such? Its quite difficult to break polycarb, and I’ve never heard of it *shattering *unless it was well below room temperature or had been in the sun a few years.
Rivets are fine, if you put the wood on the side with the flange. If you have wood on the blind side, use a washerof the appropriate size. Note - these are snug-fit washers made for rivets. Washers for threaded fasteners have oversize holes and will not be gripped properly. Don’t forget to account for washer thickness when selecting a rivet grip range.
We generally do multi-part polycarb belly pans, usually one piece covers the “back”, one piece covers the “front” and a skinnier piece is mounted like a bridge between the two in such a manner that the drive motors and transmissions are left exposed. We typically use 1/8 in polycarb and we try to support the edges as much as possible. We like the polycarb because it is non-conducting (which isn’t as big a deal since the cRio is gone, but it is still a good safety net if a wire comes loose) and it is very easy to work with, we can cut it quickly with a band saw and we can bend it easily in house. Polycarb does not give you the structural rigidity that a metal pan would, but for us they are easier and cheaper to work with.