Our team was considering fiberglass for this years robot. We are a third year team and have used extrusion for the past two years. We decided to use aluminum square 1x1 tubing for our drive train. But for our manipulator we were thinking of using fiberglass to keep our center of gravity low. We have never used fiberglass before and we were wondering as to specifically how to join fiberglass square tubing (from mcmaster’s) together since we could not weld it like aluminum. Any help on fiberglass would be greatly appreciated.
You can get 5’ sections. You should use 1 piece for each section of the arm. Do not use normal metal techniques. Avoid drilling holes in the pultrusion. Clamp things onto it. For where hinges and joints will attach to the ends, bolts can be embedded in ends with filled epoxy. Tube in tube construction works very well to reinforce the ends where the major stresses are. You’ll need some laminating epoxy, 2 Lb 2 part urethane foam, 1/4" chopped carbon or fiberglass. Try to avoid imparting stress on a single point. Spread it out over an area. We made our arm out of fiberglass last year and it was amazingly strong. The arm weighed 23 pounds complete with motors. If it was aluminum, we calculated it would have weighed 44 lbs.
Team 93 used fiber glass impregnated plastic last year on our upper frame. It worked out really well, only one piece of it ever broke. To attach it to other members, we milled down a piece of structural aluminum to a press fit inside the fiber glass and tapped the hole of the aluminum.
We built our entire robot out of extruded fiberglass from Creativepultrusions.com. They have angle and tube, c-channel and I-beams etc… You can use lock nuts, washers and bolts and even bolts that can be counter sunk if your fiberglass is thick enough. Fiberglass kits from Home Depot work great too, just scuff up the surfaces you want to fiberglass together. The kit comes with the resin, hardner and some kind of nylon cheese cloth. Attach the cloth around the joint and fiberglass away.
If you need any help....coachfredi@hotmail.com 602-764-3000 ext 60233
Ask for Fredi Lajvardi
Also checkout Creativepultrusions.com and contact them if you want expert Help!!! Please tell them Carl Hayden High School team 842 sent you.
just a quick safety reminder - even though the extruded fiberglass looks and feels pretty solid, it’s still fiberglass. If you cut it and/or drill it, you expose a bunch of tiny glass fibers that hurt and itch like heck if (when) they get on your skin, especially your fingers. Be sure to seal them up good and use gloves when handling.
Also, engineering wise remember that the elastic modulus of fiberglass is on the order of 100-300 ksi versus aluminum which is 10 Mpsi, so check your deflections if it’s going to be highly statically loaded. Conversely, this makes it better than aluminum for absorbing shock coming from “rigorous interaction with other robots” (except a direct hit since it’s more brittle) since the spring rate is much lower.
Yes, using 1/4" wall will yield an arm more than strong enough for the tetras and rough play. However the weight penalty and the effects on cg are not good. 1/8" wall is much lighter. If the ends are reinforced with tube in tube you can have almost the same strength with a weight savings. Think double butted tubing.
