shock absorbtion in R/C servo linkage

[BrendanP]

I have 2 servos controlling throttle and choke on a small petrol motor. I was told that in the case of a back fire the butterfly valve in the throttle body can be violently moved open or shut. This force is then transmitted to the servos via the control cables which can damage the servos gearing , bearings etc.

Is this true? If so what can I do about it?

I was told that one idea is to bend a 'Z' in a piece of piano wire and have that as part of the control linkage, the 'Z' allows compression or tension movement and so provides some 'shock absorbtion'.

Is there a commerical soloution for this problem off the shelf. I thought R/C models might have to deal with a similar problem from time to time.

 

[joe of loath]

yes, they are servo savers. they are 2 peices of plastic with a spring in the middle. the servo will keep it still and the arm attatched to the cable will move. the spring will then move the linkage back. i see you are in the us. search on tower hobbies for servo savers.

p.s. for any other RC related questions use RCtech.net i am an active member there, and there are hundreds of other people ready to help.

 

[craig008]

it depends on ur linkage, i would go to a model shop to see how they get over the problem. on remote controlled car its the plastis arm with a spring and a stop slider.
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FERRARI F50

 

[BeanieBots]

As stated by Joe of Loath, they are called "servo savers" and have various forms. Normally two sprung loaded plates. Throttle linkages are are usually pre-tensioned sprung loaded rods that will "give" when excess load (often the the throttle stop) is applied. The "spring" also affords shock/vibration absorption.

 

[BrendanP]

Thanks guys, I'll follow up the advice re. the R/C forum Joe.

 

[Wrenow]

Oh, and, the "Z" bend also works. How well depends on the size of the Z and the stiffness of the wire. Another possibility is using two "parallel" wires, one on each side of the servo arm, knd of like

 _._
<_._>

or
 _._
(_._)

driving opposite sides of the throttle linkage. If you put a bend or curve in them, they will provide some "cushion" and positive turn without the possibility of over-turning and locking.

Servo savers are more elegant, of course.

Good luck.

Wreno