Alternatives to aluminum tube

More design questions:
I need a stick-like thing, about 30 inches long, to go from a pivot point to a little electric motor. It needs to be moderately rigid,
light and inexpensive in lots of 50 each or so. It would also be quite nice if it's moderately attractive -- mill finish aluminum without too many scuff marks is just fine for this. Prettier is better.
I'm thinking that thin-wall aluminum* tube of about 5/8" diameter will work well, and I'm getting ready to be shocked once again by how much things cost these days. While I'm waiting for quotes, I thought I'd solicit the group for suggestions.
Fiberglass? Carbon fiber? Phenolic? Other plastics? Titanium**? Extra thin-wall steel? Balsa wood comes to mind, but while it is low tech I suspect it'll cost more than aluminum. Cooked spaghetti is too limp, and uncooked is too brittle.
Anyone have suggestions? Do you have supplier names to go with your suggestions?
* Alloy isn't terribly important. Even dead soft would work, although harder would be better.
** OK, maybe it's more expensive than aluminum.
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Tim Wescott
Wescott Design Services
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pvc pipe? venetian blind replacement rods? wooden dowels? you don't give a lot of specs on size or what kinds of forces it has to withstand, whether it has to be weatherproof, etc.
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On Tue, 11 Mar 2008 11:01:30 -0700, charlie wrote:

Your "venetian blind rods" turned into "polycarbonate tube".
McMaster sells polycarbonate tube -- they have some 1/8 wall 5/8 OD tube that should be OK, if a bit more brittle than I'd really like. They want less than $2.50 a foot, and I should be able to get it for much less elsewhere if I dig. I'll see what else they have.
Thanks.
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Tim Wescott wrote:

You can get 5/8" hardwood dowels for less than $.50/foot.
http://www.hobbylinc.com/htm/mid/mid7910.htm
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Why bother, when you can get sticks for free?
John Martin
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John Martin wrote:

So I'm going to be including the cost of these things (A $x49 value!) in a high-end seminar, and you want me to put it together with stuff I find in the woods behind my house?
Hmm.
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Tim Wescott
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wrote:

1/2" CPVC pipe might work. It is readily available and not very expensive.
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Just a thought, Tim.
Several years ago we needed some very light, thin and very flexible wire to connect sensors on the pick-up-head of an old pick-and-place machine. The wire was subject to a lot of torque as the head rotated to the correct theta to place the part. Original wire was unobtanium.
I found a source of two conductor litz wire on Ebay. It was from England and was for hi-fi record pick-up heads. I think I ordered it from them a couple of times. It had one copper wire and one gold wire. The copper was insulated and the gold was twisted around the copper. The guy sold it by the meter and a meter was good for a couple of years for us. Something like this would power your fan motor and not add much weight to the arm. I am sure this will be a question in the near future :).
Paul
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On Tue, 11 Mar 2008 14:32:16 -0700, pdrahn wrote:

I actually have the circuitry, wiring and software issues well in hand. I even know where I'll be getting motors and propellers.
Hard to believe, I know, yet it's true.
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Hi, Tim. Should I say "here we go again!"? First, how will it be fastened to your device? Will it be twisted, pushed or pulled? Will it matter if it is solid or must it be a tube?
The first thing that comes to mind is using a piece of the white resin electric fence post available in your local farm store. These are either 3 or 4 ft. long and about 1/2 inch or perhaps 3/8 inch in diameter. We cut pieces off to use in a customer's product. I am not sure of what it is used for, but sometimes I am sent to buy another stick or two. They are quite stiff, but light.
If you want to look at carbon fiber tubes or fiberglass tubes, go check out an archery store. They have both for the local arrow makers. They might even cut them to the length you need.
The most critical factor with tube is crushing it when you make attachments.
Good luck!
Paul Drahn, President Jodeco, Inc. Redmond, OR
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On Tue, 11 Mar 2008 11:16:23 -0700, pdrahn wrote:

Asking dumb questions helps me think through all the details.
It'll (most likely) be glued into a hole (in a counterweight) on one end, and either have a motor/propeller assembly held to the other with an elastic on a peg, or a little ducted fan unit held to the other with a tapped cross-peg or an expandable plug (if I can find one).
In normal use uncooked spaghetti would work, it mostly needs strength to avoid damage during handling and while the student is learning about stability and overshoot.

I'll take a look the next time I'm at Wilco's.
<balance snipped>
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This seems to be an ideal application for virtual reality. That way your device could be made from smoke and mirrors!!!!! As stiff as you want and NO weight!
Sorry, just had to suggest this, but know it's not practical for the few you are designing for. Would be fun, however.
Paul
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On Tue, 11 Mar 2008 13:51:17 -0700, pdrahn wrote:

I could 'make' these things as simulations a heck of a lot easier than I can make the physical article. But control systems implementation is often very hands-on; having a sample of the real thing, in a way that's fun, slow enough to see what's going on, noisy enough to get a visceral feel for it, and the right size to grab, is the right thing to accompany what I'm doing.
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..
Unless you've ruled out aluminum tubes completely, try
http://www.texastowers.com/aluminum.htm
- Pretty good properties
- UPSable lengths.
- Cheaper than a lot of other stuff.
- Adjacent sizes in the list telescope too.
- If you insist on 6061, google for OnlineMetals.com
Hth, Fred
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How about a hardwood dowel? Easy to find in craft shops or woodwork places, diameters 1/4" to 3/4", and with some effort (sand smooth, wax, wrap with a string and friction-polish) you can get nice surface appearance.
A length of bamboo could do, too, but unless you have a weedy patch of the stuff in your backyard, it's gonna be hard to find a source of short sticks.
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wrote:

Dollar store bamboo plant stakes @ 12/$1 Gerry :-)} London, Canada
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    Hmm ... does it need to be more rigid in one direction of rotation than the other (e.g. more load with clockwise rotation than with counter-clockwise?) If so, then either carbon fiber or fiberglass, laid with the right fiber orientation would probably be stronger. (Note that this is presuming that you are transferring torque through the tube from the motor's shaft.
    If you need it stronger in compression or tension, then other choices might be better -- though tension would do well with either fiberglass or carbon fiber.

    Thin wall? Is it being used for torque (as I suggested above) or just to hold a motor tensioned against the belt or gears?

    Define how you are planning to use it, and perhaps we can come up with better selections.

    Especially if it needs any working to make it the right shape.
    Enjoy,         DoN.
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DoN. Nichols wrote:

Neither. The tube is pivoted on a horizontal axis, the motor has a propeller on it that turns the assembly on the pivot. The only working load that the tube has is the weight of the motor and any transitory loads from the thrust of the propeller while it is accelerating the assembly.
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Tim Wescott wrote:

How about economy grade hunting arrow shafting? I know its smaller than 5/8 but unless your motor weights a couple pounds or something it should be fine. It's fairly thick walled so drill and tap each end to facilitate attaching the counterweight and motor.
Regards Paul
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On Tue, 11 Mar 2008 20:47:26 -0600, Paul wrote:

...
The description in an earlier thread (see beginning of any hit at http://groups.google.com/groups/search?q d8e61b8f8f6fe4 ) refers to "a propeller on a stick. You mount the propeller on a motor on the stick (light aluminum tube), you counterweight and pivot the stick so the thrust of the propeller will move it easily, ..." [for use in control systems seminar workshops] so I suppose TW probably will use a few ounces of DC PM motor with fairly low current draw.
I think 6063 .75x.75x.06" tubing, at under $1/foot, is probably a dollar less per beam than arrow shafting, plus being easier to attach to the axle. In TW's plan, the beam is fixed to the axle, which rotates in bearings and turns the sensor pot that provides feedback to the PID controller. One way to save on bearings would be to glue the pot to the side of a .5" (.840" OD) PVC pipe in line with a drilled-through pivot hole, and use a fixed axle. Schedule 40 .5" PVC at .17#/ft is slightly lighter than the aluminum tubing, and .75" PVC at 0.226#/ft is slightly heavier. Both have about 0.11" wall thickness in Schedule 40 so are fairly stiff.
-jiw
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