Oh boy, now you have no excuse for not building that robot! Nothing is easier or faster than building with extrusion and we've added 20mm square aluminum extrusion and components to our catalog. This product is the extrusion itself. Made of aluminum, its exactly 20x20mm square and has slots on all four sides. You can use T-nuts that slide into the slots to connect plates, couplers, PCBs, cut-outs, etc. Its sort of like a big-sized Erector set.
We like the 20mm for being just large enough for sturdy DIY projects and robots, but not too clunky and heavy. Each piece here is 610mm long (2 feet), and is easily cut down with a hacksaw or bandsaw. Grab some T-nuts, screws and plates to build a frame, then finish off with end-caps.
Slotted Aluminum Extrusion - 20mm x 20mm - 610mm long (2:10)