Re: Servo gear stripping question

It happened twice to me that I killed and aileron servo in a nose-on crash, with no other damage to the ship (apart from a few dents). In
particular, I don't think that anything hit the ailerons or the connection. These are 9euro micro servos with plastic gear. What happened is that, I think, the wing tips flexed forward which caused the aileron to be forced upwards violently. My question: is there a way to save the servo from excessive and sudden load (apart from not crashing, of course), for example by introducing a weaker point somewhere else, which is easier to repair? I have a u-bent in the rod (music wire), but it is clearly much stronger than the little cogs in the servo.
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lataj
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There are servo arms for car throttles that have a device in them but it is NOT recommended for Ail. Ail needs a better servo because it is an important function. IMHO mk
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What you are seeing is reasonably common in the lightweight electric genre but more frequently with 2 aileron servos. The weight of the ailerons at impact forces is in excess of the servo gear train. Use a smaller diameter of music wire as that should help with the problem.
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This is piss poor advice - do what MK suggested and put a couple of 10-12 gramme class servos in there.
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Boo

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Really it depends in the plane. I have foamys that use flimsy wire and that probably saves those little 55 servo gears all the time but these planes don't trim for pattern either. His plane my be worth less than good servos cost. mk
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I'm sorry if I seemed to be putting words in your mouth mk. However I do think that putting flexible linkages on any major control is a bad idea for a toy aeroplane, park flyer or otherwise.
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Boo

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Generally true.(pull pull to be the exception). Make sure UP is a PULL function. :) mk
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:-)
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Boo

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Think I'll consider bigger servos, they are cheaper anyway. And very close to the COG in my case, and my planes are too light anyway. I am not sure using any kind of spring loaded linkage for ailerons is a good idea. I am afraid of the ailerons starting to flutter in a dive.
lataj
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lataj
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I'm sure you will be happy with this solution lataj, it's what I did when my EPP slope soarer broke all 4 of the HS81 servos in a crash - replaced them with metal gear HS85 servos and never had another problem.
Good luck,
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Boo

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Good luck, let us know how it goes. What plane is it? mk

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A little stressed are we? How much more than his aircraft should his servos cost? How much more than his naked airframe should his servos weigh?
While I agree, in general, with your apparent thesis about inflexible controls I don't think he should be carrying big servos in a small park flyer which is what it takes to survive the type of impacts he is experiencing without using the more flexible sizes of music wire. It becomes a matter of practicality. You MIGHT have noticed that this was NOT recommended for an elevator application, or not as your short fuse dictates. . .
Having said that, there is no reason a more flexible size of music wire would be the wrong thing for the elevator if it was set up properly (UP pull rather than push) as MK noted.
YOUR MILEAGE MAY VARY!
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????
> How much more than his aircraft should his servos

Depends, doesn't it ? And if he has to replace the broken ones anyway then why is it sensible to pay for ones which are just going to go the same way as the last lot ?
> How much more than his naked airframe should his servos weigh?
Well, IIRC the ones fitted are 8 gramme class servos so that would be an increase of 4-8 grammes in total. I don't know how much the airframe weighs but you can carry 8 gramms in eg a Shocky without it being a disasterous encumberment so I think your point is misplaced.

I don't think 12 gramme servos are "big" compared to 8 gramme ones. 12 gramme servos will readily fit in most park flyers maybe needing a small amount of relieving with a scalpel blade.
> which is what it takes to survive the type of impacts he is

> Having said that, there is no reason a more flexible size of music wire > would be the wrong thing for the elevator if it was set up properly (UP > pull rather than push) as MK noted.
Aileron controls are not less important to the flying qualities of a model than elevator controls and I don't think flexibility in the linkage is acceptable in either case.
I wasn't trying to annoy you SO'CH, but I really do think the better way forward for the OP is a slightly beefier servo. This is particularly true if the originally supplied ones came with the kit - IME these are very often far too flimsy for the job.
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Boo

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Whatever.
I don't by RTF.
When I buy wimpy special application servos, I usually install them in such a manner to insure their survivability. Flexible linkages have their place if properly used. It only takes a little thought and the installation should be obvious.
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How about one of the linkages usually used on throttles. It has a quick link on the servo arm with a hole large enough for the rod to pass through the link with a spring on each side, with the springs retained on the rod by wheel collars.
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Jim in NC



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