[Tristan Lall]

McMaster is a bit strange with regard to shipping to Canada (provided nothing has changed in the last several months). They'll happily and promptly ship to existing customers, but I've heard several times from potential Canadian customers that they're being turned down.

Since you're in Kincardine, maybe one of the Bruce Power folks can arrange for you to ship it to their dock? (Surely they've got a prior relationship with McMaster.)

As for belly pan materials, laminated carbon fibre and plywood was just what I was going to suggest. Companies like DragonPlate sell it, and it's expensive but excellent. I've never been able to afford enough of it to use on an FRC robot though.

Garolite can work too, though I've never seen it laminated with a lightweight core. You may have to build your own using a high quality epoxy and some appropriately smooth plywood or other material.

With any of these composites, machining can be a bit of a pain (not to mention the dust is nasty). If you still have a way to get some parts cut on a waterjet, that may be the thing to do, provided that any wood core is marine grade (or similar) so the glue won't dissolve, and doesn't expand too much when wet. (I seem to recall that DragonPlate says they've tried this with their plywood-cored material, with decent, but cosmetically poor results.) Otherwise, they're usually cut with a CNC router (but the material wears out cutting tools quite quickly).

I'd actually be interested in seeing how progressively-stiffer robots perform on the playing surface. There's probably a point where more stiffness becomes inconsequential in any given design, and it might be worthwhile to experiment with several materials to try and find it.

One final thought: in most designs using one, the belly pan is probably most useful as something that keeps the frame rectangular, rather than something that keeps it from bending in the vertical direction. In that sense, buckling resistance in 2-D is probably more important—and that has a lot to do with the way you attach it to the frame rails. (Lots of rivets are good!)