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Bellcrank setup

Old 12-28-2003, 08:48 PM
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john flynn
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Default Bellcrank setup

Gidday all, by looking at the image below, can anyone tell me how to determine the optimal position to connect the pushrod onto the bellcrank? I know that the further in to the center the more movement but more strain on the servo and the further out less movement but easier on the servo. Is there a formula to determine the best position? Thanks for any assistance given. Kind regards, John.
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Old 12-28-2003, 11:57 PM
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swooper
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Default RE: Bellcrank setup

Seems like it would be best to set up the servo-to-bellcrank link so that full servo travel gives the desired full rudder deflection.
I would make both the servo arm and the link position on the bellcrank long to minimize free play.
best wishes!
Old 12-29-2003, 01:26 AM
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3DFanatic
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Default RE: Bellcrank setup

Can you avoid using the bellcrank alltogether? Installing a bellcrank is automatic slop in whatever they're connected to.
Old 12-29-2003, 06:36 AM
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john flynn
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Default RE: Bellcrank setup

Thanks for the input fellas. So long as the pushrod that drives the bellcrank is sturdy, kept short and straight and the keeper holes for the clevises are the right size, the system will be no more suseptable to slop than any push/pull setup. A symmetrical closed loop from the bellcrank to the control horns remains in constant tension so no slop is possible that side. Swooper, what you suggest is what I want to end up with, I guess I'll have to make a mock up to achieve it. I was just going to drill a series of holes down one side of the bellcrank and try em all to find the right spot. But I was hoping someone could point out geometrical formula I could use instead of all the mucking around. Thanks again for your help men. Kind regards, John.
Old 12-29-2003, 03:10 PM
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nashtm
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Default RE: Bellcrank setup

It all depends - its a trade off between torque and throw required.
I now try to avoid bellcranks as thet do introduce some play - even if you have no slop the slightest amount of play ( even a tiny amount) at the center pivot causes poor centering of the control surface.

Tim
Old 12-29-2003, 07:19 PM
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Default RE: Bellcrank setup

If your servo arm is 1 in from the pivot point to the pushrod hole and travels through 60 degrees and the bellcrank is drilled 1 in from the pivot point, the rudder will move through 60 degrees also. If you drill 2 in. at the bellcrank the rudder should move 30 degrees. Correct me if i'm wrong.
Old 12-29-2003, 08:18 PM
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john flynn
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Default RE: Bellcrank setup

Thanks Flypaper, that's the sort of info I'm chasing. Before going ahead, I might just wait for a bit and see if anyone extends or disputes your data. Kind regards, John.

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