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Dynon Servo shear screw replacement

ben barron

Well Known Member
Patron
My roll servo stopped working on my last flight. Jeff at Dynon gave ma a simple test to confirm it was a failed shear screw, which I did. I now need to install a new screw. Has anyone out there done this? Can it be done in place? The new screw goes in a new hole. Will the servo re-set it self as the arm will be in a different location to align with the new screw?

Dynon sends out (at no cost) a new screw when you reach out and then fill out a form. Www.dyninavioniocs.com/guides/servo_shear_screw_replacement_instructions rev_E.pdf
 
I’ve replaced both pitch and roll, but it’s not a big deal. Yes you need to remove the servo but getting access is pretty simple. Which hole you use is immaterial as when you are finished, you’ll go back into the software and run the setup app again.
BTW, at least in the RV10 servos, the replacement screws are noticeably beefier than the originals and I haven’t had any issues since.
 
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shear screw

I was able to replace the shear screw in place on the aft "roll" servo. One has to remove the arm by pulling the castle nut ,this gives access to three screw holes, use a new screw hole for screw and locktite. The arm will reposition its self . Was a lot easier not having to remove the servo. Works Great, Good Luck RV 12
 
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For you guys who had broken shear screws can you attribute it to anything unusual or is the design just susceptible to the problem?
 
A couple of years ago I sheared the pitch shear screw in my RV-12. This was due to my over-enthusiastic movement of the stabilator during a period of aerial messing about. The shear screw is easily replaced using the Dynon-supplied kit. At that time Dynon told me that they had strengthened the shear screw to make such issues less likely. No problem since.
 
shear screw

My shear screw broke because off runaway trim. I was correcting the condition before the autopilot was disconnected. My autopilot has been a problem trimming nose down and full left roll, so my immediate correction was needed! Dynon and I are fixing the problem. However it seemed to shear quite easily,worked safely and as designed. Ben
 
The old shear screws are easy to shear, I once had a pitch issue and when I went to check to see if the screw was loose, all I did was checking with an allen wrench and it broke with very little tension applied.
 
I had broken shear screw on the pitch and roll servos in my -7 this past summer. At first, I noticed that the AP would not hold altitude, occassionally at first, then more frequently. After I replaced that shear screw, I discovered the shear screw in the roll servo was also broken when I was trouble shooting a frequent AP disconnect. No AP flight anomolies associated with the broken roll servo shear screw that I could detect; the frequent AP disconnect was apparently due to some conbination of a faulty roll servo circuit board and/or intermittant ground.

Dynon indicates that their new shear screws are more robust that the early ones.

Warren
RV-7, 300 hrs
Minneapolis
 
New Design Shear Screw

The new design shear screw was available late in the 1st quarter of 2017. It was a redesign due to a premature fatigue failure of the old design screw during normal use.
 
With a call / email to Dynon tuesday, they sent the new roll servo shear screw via USPS so i recieved it 2 days later. The part came with lockTite, Allen wrench and cotter pin all at no cost. That?s great service.

It was Easy install in place.

My question now is with a 2015 vintage servo should i be changing out the pitch servo shear screw? I would like to avoid failure in flight when i need it.
 
Ben,

Same thing I am thinking. My servos were installed in 2012 and have 800 hours on them. Sounds like I should replace them at annual.

Rich
 
Well, my pitch servo shear screw failed, but I am posting because the way it failed made the test results ambiguous. When the screw sheared it left a nub sticking up through the hole in the actuator arm so instead of no resistance to movement of the elevator it had about 15 degrees of servo shaft rotation as a dead zone. What was happening was the servo would try to put in the proper elevator position and rotate through 15 degrees until the nub contacted one edge of the hole in the arm. Then the arm moved, but to go in the opposite direction the servo had to rotate 15 degrees for the nub to contact the opposite side of the hole and move the arm. Had it been a clean shear there would have been no resistance to manually moving the elevator with the AP engaged.
 
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