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Old 12-14-2003, 01:15 PM
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Stick Jammer
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Default RE: pull pull geometry

Originally posted by Rodney:

It is also much less strain on the servo bearings.
At the risk of starting a huge debate, I'm curious as to why a lot of people feel there is any less strain on pull-pull servo bearings when using a bellcrank (or pulley) instead of a direct connection. The cables of a pull-pull don't need to be excessively tight at neutral, not enough to cause the bearings to wear out while just sitting there. Once the servo starts to travel and there is a flight load on the rudder (or whatever surface), that load is being equally transferred to the servo in either setup. The bearing of the bellcrank doesn't take any of the flight load. If the mechanical ratio of the setup is the same with or without a bellcrank of some sort, the flight load imparted on the servo ain't gonna change. If it did, then we should be able to use smaller, cheaper, less powerful servos for the same application. It's just not the case. I'd be curious to hear from anyone who has honestly wore out a servo bearing by using direct connection for a pull-pull.