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Complex Translation of Linear Motion through Rotating Part

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theothersully

Marine/Ocean
Dec 13, 2011
5
Hi,

I'm facing a difficult linear motion problem.

Background:

There is a wing (foil) that can rotate 360 degrees on a post. This wing is to be controlled by a "trim tab" or "servo tab", which is, essentially a smaller wing just behind the main wing. The purpose of the small wing is to "steer" the larger wing and cause it to go from no lift to producing lift, but altering the angle of attack.

I need to use some type of control to steer the servo tab to either side, and I'm trying to do it mechanically, rather than with motors.

Ideally, somewhere on a table nearby, there would be a small joystick that says, "neutral" in the middle for having the servo tab perfectly aligned with the main foil. Then, there would be "left" and "right", allowing you to push the joystick to the left and right to move the servo tab left and right up on the wing.

Problem:

It needs to be mechanical. If the wing didn't rotate 360, a set of cables would do the trick nicely. BUT... the wing rotates through 360 and the cables would get all tangled up.

Question:

How can I, mechanically, translate the linear action of a joystick type lever as described above, to the servo tab on the wing, even when the wing is free to rotate through 360??

I would imagine this problem has come up in engineering before. I'm just a Physics (theory) guy. I'm kind of stumped on this one.

Any ideas?
 
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Somewhat like what I believe is the collector in a helicopter rotor. A thrust bearing arrangement operating linkage to rotate the servo tab. Flyball governors may be similar in action.

Ted
 
Thanks!

You guys are definitely onto something here.

This is what I first pictured, but since I only need one linear arm coming off the rotating piece, I figured it would jam or slide poorly with all the force on one side of the rotating collar.

Any tips for making a rotating collar like that ride smoothly up the shaft when all the force is on one side?

Also, we think alike again! I was looking at pictures of old mechanical governors just an hour ago.

Thanks for the input.

At least I know I'm sort of on the right track...
 
You might also consider a clutch throwout bearing arrangement.
Make the throw mechanism slide engage the shaft by at least two diameters to make it stable and remain aligned with the rotating shaft so it slides without binding, tilting.

Ted
 
"I figured it would jam or slide poorly with all the force on one side of the rotating collar."

You are seeing that picture in your mind because of the geometry between the collar and the shaft on which it slides. For example, if the shaft is 1" diameter and the sliding collar is 1" thick, then an offset force will cause binding. Its the ratio between the sliding diameter and the collar contact length that determines the potential for binding.

So.... make the contact length of the collar longer. In the example above, if the collar length was 4" instead of 1" it would be less likely to bind. In the field its known as "bearing separation".

Another solution presents itself in that word: "offset". If you can load the rotating collar at two symmetrical points instead of just one, the offset disappears. Think of a Y-shaped "yoke" that holds two rollers at opposing symmetrical contact points on the collar.
 
Amazing level of expertise here. I can't even thank you guys enough for the thoughtful and inventive answers to my question.

I think I'm all set at this point. All concerns have been addressed. Now, it's time to draft up and build this thing.

Thanks!
 
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