View of the belly pan for the off season drive train we are working on. We have always built heavy robots, including belly pans (either un-pocketed 1/8" or 1/4" poly) so we decided to see how light we can build things. This 1/8" aluminum belly pan was water-jet by a sponsor.
Very nice. What did it end up weighing?
How much did the pollycarb belly pans weigh vs this?
Guessing off CAD (haven’t had a chance to weigh it in real life), ~3 lbs.
In comparison, the same size poly carbonate in 1/4" would weigh roughly 6.5 lbs. We could drop down to 1/8" in comparison since we have never really needed 1/4" besides 2016, but that still is only 3.25 lbs roughly. We just decided to experiment with using a fancy belly pan and test out how light weight we could make something.
I would HIGHLY avoid polycarbonate belly pans unless you know for a fact that it is electrostatic dissipative (ESD) polycarbonate.
If it isn’t ESD polycarb, you will build up a lot of static electricity and zap your electronics.
2018 was actually the first year as far as I know that my team did not use a polycarbonate belly pan. I know 2017, 16, 15 and I believe 14 for sure had polycarbonate and as far as I know we haven’t had any sort of failures from static electricity. I also have no idea what type of PC we use. We acquire all of our polycarbonate from local automation companies that consider 3’ x 3’ scrap considering they use it as windows on large machines.
Wow, that looks really sick! Looks like you could cut some weight out of the team number though.
The Aesthetic value is too much (unless you make all the holes in the shape of the team number).
That is a seriously nice belly pan!
would it hold up under the weight of a full robot though?
That’s part of the reason we are testing it now. Itll be used in a WCD so the tubes should act to stiffen the pan up. The only thing mounted to the pan are electrical components and then the battery. The only thing we are worried about is the load from the battery but there is another plate that mounts above to help truss around the battery.
Looks freakin’ sweet
As a sign of respect, I’m going to pick it apart a little bit
Structurally, the bellypan acts primarily as a shear plate - the border alone won’t do anything that a set of 4 typical versabrackets can’t. The contribution to chassis stiffness is driven by the fact that the bellypan prevents the frame “trapezoiding” on you. Your hex pattern will introduct some springiness in that direction, compared to solid or to a diamond pattern that is laser-focused on preventing shear.
If you want to run a true engineering study, I’d be very curious to see how the stiffness compares to solid 1/8" Al & 1/4" PC in rigidity.
Build up the frame with a test bellypan, clamp the back rail into a heavy workbench, apply load to the front rail and measure force vs displacement with a dial indicator in torsion and in lateral shear? With a decent dial indicator you shouldn’t need to put more than 100lbs on the chassis to see enough displacement to make a calculation (lbs/degree). Repeat for a second or third bellypan style. Compare weight to stiffness result. Consider cost. Write it up.
Of course, now that we’re measuring stiffness… what’s a good-enough stiffness value? Race car designers generally go “as high as possible”, but an FRC bot is not a racecar… YMMV. :]
Note that everything I just suggested doing is far beyond the scope of typical FRC team projects and comes much closer to real-world engineering. You’re already successfully piloting new design processes, new fabrication workflow, and are in progress to demonstrate the real-world feasibility of this design - great job! Keep it up!
EDIT: To be fair the actual modern engineering case study would be to model a subset of your scenarios in an FEA package, cost them out, pick the best, and then test that one setup with a few samples, to make sure it matched the FEA model. Full scale tests are expensive…