Linear positioning

Hello,
ik would like to build somthing like this: http://users.pandora.be/Ivevanlee/helpme/Untitled-1.html
many off-the-shelf stuff works only straight and I would like to build a
cheap version myself. If there is a good off-the-shelf product I would very much like to know about it!
Controlling a stepper trough a computer is no problem and I have programming experience. Just absolutely no engineering experience :) Can anyone point me in the right direction or answer questions like: - is connecting a stepper the right way to go? - what kind of wheels should I mount on the stepper? - what kind of rails should I use? - are any of these components easy to find?
any information you could give me would be welcome!
many thanks,
Ive
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    --Well I'd start simple and go with model railroad stuff, then scale up from there. What sort of load were you expecting to apply; i.e. how much torque will you need to hold position/change position?
--
"Steamboat Ed" Haas : There's never a tachikoma
Hacking the Trailing Edge! : around when I need one!
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steamer wrote:

that's a good idea. It should support about 1 kilograms (2.2 pounds), or a little more. However... the weight extends to the middle of the arc (not completely).
ok, some pointed me to this: http://www.hepcomotion.com/db_pages/products/proddetail.php?id 29&cat=circ
that's what i'm looking for... it's just really expensive... not sure if I could build that myself :)
Ive
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This is too vague. Tell us, clearly, what you're doing.
If you only have a load of 1 kg, consider curtain track, used for draw drapes. There are motors for such things. Here's a useful system.
http://rongli-cn.en.alibaba.com/product/50008398/50051379/Motorized_Blinds_Track/Curved_Track_With_Motorized_Remote_Control_Unit.html
                John Nagle
Ive wrote:

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Hi Ive,
I missed the beginning of this discussion, and it's overkill, but would the mechanism of an automatic garage door opener do? Could be cheap, especially a used one...
Peter
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I worked on a comparable project for a theater a while back, to move a large animatronic figure.
We ended up just putting the animatronic figure on a wheeled base, with an arm extending out to the center of its arc, where it connected to a pivot point. This arm was pushed and pulled by a linear actuator. It ended up being a fairly long one, because if we put it too close to the pivot point, then we would have needed a much stronger actuator.
The benefit of the above is that the object tracks very accurately on the arc. The drawback is that the movement is not linear in relation to the actuator, plus the need for a fairly long or strong actuator.
On another similar project with a flatter curve, the animatronic figure was placed on a skid and a simple track was made by putting angle and curved bar on a plywood base. The skid just slid on the wood between those tracks. The skid was moved by a belt that ran underneath it,but on top of the plywood. The belt had a small skid of its own with a pin sticking up to make contact with the Animatronic skid. The line of the belt was actually straight, but the pin was allowed to slide in its relation underneath the large skid.
This idea is definitely not a precision positioning technique, but it was simple!
Joe Dunfee
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Joe wrote:

well, the problem is that i would like to put mount it somewhere, mid-air. so i'm looking for a sort of light rail of some sorts. and some wheels. And even then i'm wondering if that would be precise enough. I have no experience with that.
another thing is that i don't have to middle of the arc as a resting point...
Ive
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The curved curtain track was a good idea. But, perhaps you want your trolly to sit on top of the track.
Perhaps a cheap way to go is to get steel or aluminum bar (perhaps 1/8" x 1") and bend it to the shape of the track you want. Then your "trolly" can have flat wheels that sit on top o the rail, and wheels on the side that keep it upright and guide it along the track.
To drive it, you might fasten a length of timing belt along the outside of the track. Then, your stepper motor would need sprocket that mates into the timing belt to drive it.
Joe Dunfee
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