High-density polyethylene is one of the materials considered for the gearbox. It's important that the gearbox does not warp over time or deflect under pressure of the shafts; either of these could cause binding in or slipping of the gears.
Xyloy is a metal that can be used in the same molds and processes as injection-molded plastic, with no further processing needed. B9 has the capability of using Xyloy; we considered using it especially for our gears and sprockets.
Plywood is cheap, lightweight, and relatively strong. We considered its use as a back for the seat assembly, as structure inside the bucket, and as plating to connect the gearbox to the seat assembly's track.