What type/shape of metal ( i.e. tubular aluminum) should I use for a robot frame?

I am building a robot. It will be about 1.5 meters long, about 30 centimeters high, about 40 centimeters wide ( all dimensions excluding wheels, tracks, etc.). It's body will be a metal frame with an outer fiberglass shell. The frame needs to be strong, lightweight, and rugged. It would also be nice if the frame could be welded with a homade stick welder, but that isn't a primary concern. Any advice is appreciated. Thanks!

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recon5068 years ago
This would remind me of a design I played around with for a battlebot a couple years back... Since it doesn't seem that you have access to an Advanced Squarewave AC TIG Welder and a pure Argon gas tank, your best bet would be steel. However, if you are cool with not welding it, you might want to look into Structural Aluminum kits, that come with pre-fabricated connectors for all sorts of angles. Structural Aluminum is basically a honeycombed solid bar of Aluminum. It is light, but at the same time it has more structural integrity that your run-of-the-mill steel tubing. (Unless it's 4130 Chromoly, but then you'd obviously know more than me, and as such what would you need me for?) Kits are fairly cheap, and the bars themselves would run you about 75 cents per foot length of 1"x1" standard bar (that's 6061 T65 Alloy). Now, if your homemade stick welder is AC, you may have a chance of welding your Aluminum. It wouldn't be pretty, but if done remotely right it will hold your robot together pretty well. If you have any questions regarding anything I have said, just PM me. -recon506
i would suggest steel in the shape of an octogon
robotguy48 years ago
For a robotics team, we used extruded aluminum that looked something like this, but solid. Its nice because you can slide and adjust things easily (no welding required!) I think we got ours from Bosch.

I'd suggest not going with steel if you need it to be lightweight. Steel is freaking heavy!
Yeah that stuff is awesome... if you have a corporate sponsor. You can tap the center hole and mount special interlocking bolts in it to get nice 90 degree struts, its really easy and quick to work with, but it is expensive.
conrad24688 years ago
STEEL! hollow square tubes! but thats what i think...
or angle iron... but you have the right idea!
I cast my own parts using recycle aluminum, it works really well and parts needing welding can be soldered using alumalloy knockoff from "harbor freight" and a propane hand torch. aluminum is allot lighter than any other metal saving money on bigger servos while also retaining tensile strength comperable to steel and its cheap! the real thing to figure out is battery output verses weight . Trying to get an hour use out of it before needing recharge is the hard part for larger projects..
For a small robot, I would definitely go with aluminum. It is more likely than not strong enough for your purposes, and is fairly lightweight. Good luck, and hopefully this is helpful!
mikeasaurus8 years ago
For strength your best bet is to use tubular steel, or square pipe (HSS). However due to weight issues (and power issues too if your robot has a weak motor it won't be able to lift it's own frame) you might want to try something less bulky, like steel rods or aluminum. However, aluminum has it's own set of problems as welding aluminum is different (and much more precise) than steel, the fact that you have a homemade welder could make this very difficult. Beware.

Also, it depends on what kinds of loads this robot will be under. If there is lots of stress make sure you have solid welds. Since you are fabricating the frame you might want to try using a truss design, it doesn't have to be super beefed up, but something that will withstand dynamic loads (since it will be moving).

Based on my experience with welding and the dimensions you've listed I would recommend steel rods cut to length then welded using the above mentioned truss design.

Hope that helps!