Strong lightweight structural material

For this year Science olympiad, we have to build a robot that picks stuff and places it into a jar. It has to reach about 5 feet and lift objects up to 2-3 ounces.

I plan on making it fully automated, unlike last year one that won the Illinois State Olympiad.

I want to make it's arms to be as lightweight as possible, from some super thin material. But it has to be easy to work with. Something like thin aluminum extruded square tubing or some such. Any suggestions?

Again the arms only need to reach 5 ft and lift 2-3 ounces.

Thanks

i ===============================================================

In terms of greatest stiffness per weight of material, round tube is better than square. I'd start with very thin wall aluminum tubing like you suggested, in a truss structure. Something like three tubes in a triangle, connected by smaller short sections angled at 45 degrees to the main tubes to form a stiff triangulated structure. Something like an antenna mast.

----- Regards, Carl Ijames

Well, wood iis good, maybe fiberglass tube is better (try Grainger.com, and other industrial suppliers). Joining by glue is most rigid, and works well on glue or fiberglass-reinforced-plastic, not so well on aluminum

If money were no object, titanium boiler tubing is a standard stock item... it's light.

Fiberglass fish pole sections?

Carbon-fiber tubes are the high-end solution. There aren't many materials that are lighter and even fewer that are stiffer, which probably will be an issue in your design.

It comes in all kinds of grades. You don't need the fancy or expensive ones. Try Googling "carbon fiber tube" and you'll see what's available.

Practically all of it is epoxy-resin-based, or compatible with epoxy, so assembling pieces with it won't be difficult.

"Ignoramus23308" wrote in message news: snipped-for-privacy@giganews.com...

The front pole of my 1970's 2R is ~16mm (5/8") in diameter with a wall thickness of 0.4mm and weighs 65g per meter including the elastic cord. The rear pole is 10mm. Jack Stephenson showed me that I could stand on the middle of a slightly short (~1') scrap section of front pole supported at the ends by 2x4 blocks.

IIRC it's alloy 7005. This is the current pole material:

-jsw

"Ignoramus23308" wrote in message news: snipped-for-privacy@giganews.com...

Maybe you could buy one piece of long enough arrow shaft tubing from a custom arrow maker, then brace it with struts and stays like a sailboat mast. You might need a box or drainpipe to protect it in transport.

-jsw

"I"? Be careful that you don't get too involved and get your son disqualified.

Full automation is a very lofty goal, it would seem. How will you train it to find the object, then place it in a row with others it has picked up? University teams are still having trouble with this. G'luck!

Are you thinking "enclosed robotic arm" or "automated crane" here? Hook end or fingers which clamp the object? Where are the rules?

Thain't much here.

Long distance, light weight. For crane style, how about an aluminum I-beam for the arm? (best pic I could find)

Rotate the tower, run the arm back and forth on the tower for distance and have a triangulated pivot point

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- To change one's self is sufficient. It's the idiots who want to change the world who are causing all the trouble. --Anonymous

I looked at some sites and found

They have several types of fiber glass as well as kevlar and carbon fiber.

But my advice is to discuss this with your son. You can give him some idea of how to come up with the best material and design. Lots to consider. Co st, ease of working, etc. You might also consider a piece that is tapered. The stress will not be the same close to the robot and at the end doing t he pickup. Could also be prestressed with some kevlar or Spectra doing the prestresing.

Dan

Google "kite" "carbon fiber" "tube". You'll get lots of results.

If you get the extruded tube remember that it tends to split -- I'd connect to it with ferrules or other things that fully surround it, or back up the longitudinal fibers with a layer of roving wound crossways.

Lots of stiffness for the weight...

You spend $500 on a wee tent? Wow!

Strong stuff, Maynard.

- To change one's self is sufficient. It's the idiots who want to change the world who are causing all the trouble. --Anonymous

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Hmm ... one possible source if round would do is from "Texas Towers" -- telescoping aluminum tubing, 1/16" wall thickness in 1/8" diameter size steps. Each tube is 6' long. I used some of their product in making an antenna recently. Not sure whether this will be light-weight enough for you. They're on the web, so you can see what they have.

Good Luck, DoN.

Carbone fiber tube. 7075 aluminum for mounting and reinforcing stress points.

Carbon fiber tube from hobby shop. Epoxies well.

Don't demonstrate boastfully how strong it is to your kids - don't ask how I know this..

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"Arms as lightweight as possible" might be the wrong focus; I imagine what you actually want is fast and accurate positioning. A central tower can be heavy and still have a low moment of inertia as it rotates with a lightweight boom supported by Kevlar strands. (The tower could be fixed in place instead of rotating, but that might complicate things.) A pickup unit would slide back and forth on the boom. Have a motor and pulley at the tower; another pulley at the end of the boom; and a loop of Kevlar around the pulleys to drag the slider back and forth.

Gunner, I just received four 10mm square carbon fiber tubes (with a round hole inside).

They are clearly stronger than steel by far, and so much lighter.

Really amazing material.

Liebherr is now experimenting with carbon fiber as material to make crane booms. That would greatly increase lifting capacity of cranes because it would eliminate a lot of weight placed at great radius.

i

Should be no problem for you. But in long term usages it is important to insulate electrically between the carbon fiber and metals. Carbon is at the very end of the electrochemical series.

Dan