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Old Aug 03, 2012, 04:36 PM
Dr.M is offline
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United States, WA, Issaquah
Joined May 2011
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WARNING to all users of Solar Servo D654

The motor inside these servos is not supported by the backplate. Under the vibrational environment characteristic of a heli, it can slide down into the case and lose grip on the servo gears allowing the output shaft to rotate freely.

How I found out: following a crash of my 450, I did a few bench tests to figure out what happened. With some shaking and proding the servos while running the motor at full RPM (blades off ) I noticed inconsistent behavior from the elevator servo. What happened was that the motor inside the elevator servo case slid a few mm lower (away from the output shaft) allowing its small pinion to only make partial and intermittent contact with the first gear of the servo transmission. Under high load, the pinion would loose grip on the gear and allow the servo output shaft to rotate freely, though in static tests the servo would act and feel normal.

Solution: Open up the servo casing and add enough foam to push the motor body against the backplate. Not too much, as the servo case won't close properly, but enough to create some pressure in there.

Another issue related to gears disengaging has been reported. It was caused by the pinion on the motor shaft being installed too low for a positive contact with the first gear. See this post here:

Maiden flight report for Solar D770 added:
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Last edited by Dr.M; Nov 09, 2012 at 12:20 AM. Reason: added another solution
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