[NSRCA-discussion] Metal Servo Arms

[Bob Richards]

Earl,
   
  Good information. However, this is a static test. I think the real failure mode might be fatigue in a dynamic (vibration) environment. This is what usually causes threaded-rod type control horns to fail.
   
  Bob R.
  

Earl Haury <ejhaury at comcast.net> wrote:
      v\:* {   BEHAVIOR: url(#default#VML)  }  o\:* {   BEHAVIOR: url(#default#VML)  }  w\:* {   BEHAVIOR: url(#default#VML)  }  .shape {   BEHAVIOR: url(#default#VML)  }        st1\:*{behavior:url(#default#ieooui) }                The Al arms are quite resistant to twisting - but you're correct that the nylon wheel is plenty strong and the Al wheel stronger than either. 
   
  A few years back I tested the strength of the JR 8411 Al spline and the equivalent nylon spline coupled to stock & H9 Al arms. The test involved making an adaptor to set over a single arm and position an inch-lb torque wrench directly over the shaft. An output gear / shaft was clamped in a vise and the torque wrench used to measure the "give" point and the failure point with different combinations. All exceeded the torque rating of the servo.
   
  Nylon shaft & arm: "Give" @ 320 oz in and failure @ 480 oz in - the spline shaft twisted and slipped, arm spline damage (yet there was enough binding to retain some control transfer).
   
  Nylon shaft & Al arm: "Give @ 320 oz in and failure @ 560 oz in - shaft spline total failure.
   
  Al shaft & nylon arm: No "give" point. Crisp failure @ 560 oz in - arm spline total failure.
   
  Al shaft & Al arm: No "give" point, Crisp failure @ 1600 oz in - no spline damage, shaft broke below spine.
   
   
  Earl

   
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