Blind rivets (also called POP rivets, a brand name) let you permanently assemble pieces. Use aluminum rivets for low weight. You need a blind rivet tool to use the rivets. The tool isn’t very expensive, and it’s sold with the rivet fasteners at your hardware store.
The downside to blind rivets is that construction is permanent. You cannot disassemble the robot unless you drill out the rivets. If disassembly is required, select a drill bit slightly smaller than the original hole. Drill out the center of the rivet. If the rivet post won’t come out, use a small screw extractor (available at hardware stores), then pull out the remaining metal pieces.
To use, the rivet is first inserted and locked into place in the tool. The end of the rivet is pushed through the materials to be joined. Squeezing the handle of the rivet tool mushrooms the two ends of a metal sheath, creating a firm, fastened joint. The center post then breaks off, leaving only the sheath.
Blind rivets come in various sizes and lengths. Choose the length based on the thickness of the materials to be joined. Bigger-diameter rivets are used when you need extra holding power.
A similar idea, but not as permanent, are plastic push rivets. These are constructed out of plastic (obviously), using a head on one end and a bifurcated or pronged shank on the other. (Okay, I have to admit that I’ve always wanted to use the word “bifurcated” in a sentence!)
To use, you press the parts of the shank together and push through the holes of the material you wish to join. Assuming the correct length of rivet, the prongs spread out on the other end of the material, locking things into place.
To work properly, the length of the rivet must match the thickness of the materials being joined.