Paul,
 I wonder how long it will be until someone puts a brushless DC servomotor on
to drive the prop pitch? The rotor of the brushless motor has the magnets,
with the coils external and stationary. An encoder must also be on the shaft
of course but you could even use it to monitor actual prop rpm!  There are
lots of sealed encoders for machine tools that are in VERY dirty
environments. The electric comutation is very reliable and there is very
little wear just sealed bearings. In fact the prop end could just be
connected and only one bearing would be needed. The system is even tunable
for deadband to prevent the RPM hunting that was mentioned in several posts.
These motors are also the smallest in size of any dc motor for a given
torque. Just my two cents. Bill Jepson

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