The first question you should be asking yourself is what the purpose of the belly pan is. Depending on how you construct your chassis, the belly pan my play more or less of a role in the structure
. A well-designed belly pan can greatly improve the structural efficiency of the chassis and allow you to get the same stiffness with a much lighter design, but it's not always that integral.
The structural purpose of a belly pan, as Adam alluded to, is that it resists "parallelogramming". That is the tendency of a rectangular frame to become a parallelogram under certain load cases, usually when a force is applied at the corners or in shear. Without a belly pan, the corner attachment is the only thing that resists the parallelogram deformation. Gussets can help, but only so far. The belly pan is effectively one big gusset.
With that in mind, the structural efficiency of the belly pan is related to how well it can transmit the internal loads. If all you cared about was stiffening the frame against parallelogramming, you could achieve a similar effect by tensioning cables across the diagonals. When the frame parallelograms, the diagonals increase/decrease in length depending on which direction it's going. The cables would resist that.
The belly pan can do more (like provide electronics mounting), but the key point is that the load that's being resisted is along the diagonals of the frame. No matter what you do, that's the load path. The diamond works with that.
Quote:
Originally Posted by AdamHeard
Proper diamond has the same # of diamonds wide as tall, which leaves a strip of metal directly connecting corner to corner. This "string" is very strong (at resisting parallelograming).
|
That corner to corner strip equivalent to your "cable". It's actually a metal strip, so both diagonals contribute something because it can take a limited amount of compression as well. You have several strips (it is a pan after all) so the load is distributed among a much larger area. It's very efficient for the job that you want it to do.
If you put hexagons in there instead, you lose that direct load path. Now the load can't travel in a straight line corner to corner, it has to zig-zag around the pattern. Ultimately, that greatly reduces the structural capability and stiffness in this application. If you take a hard hit and part of your frame flexes, the hexagonal pattern is much more likely to show signs of buckling/crippling than the diamond. Even a diamond pattern that's not the same aspect ratio as the frame is still better than the hexagon. It doesn't have the same direct corner-to-corner strip, but it still has straight load paths all the way through the material.
In FRC applications it's rarely that critical unless you're designing on the very edge of the structural capability, but diamond is still objectively "better" than hexagonal structurally, which usually translates to lighter weight, since it can handle the same amount of abuse with less material.