PRE-ROTATOR

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Prerotation on this unit is accomplished with a small RC electric motor driving a sprocket and chain reduction which drives a Bendix type starter ring gear engagement of the 108 tooth gear attached to the rotor head shaft.  The motor is powered from an independent LIPO battery pack Velcroed to the mast through an electronic speed controller.  You slowly turn the speed controller up as the rotor speed comes up to avoid over-stressing the motor and drive-train--instead of just dumping full power into a dead stopped rotor system. Roger says he starts his takeoff roll at 120 rpm and turns off the pre-rotator motor at 170 rpm. If left on, the bendix does not seem to disengage and there is drag on the rotor from the motor and reduction drive.

The 10 cell battery pack puts out 30 some volts and takes a really sophisticated ground based charger to add energy to it. Larry says it takes about 5% out of the battery pack for each pre-rotation.  He said it ran my 24 foot blade up to 170 rpm at his 1300 feet elevation and should take them to 180 at my 6500 foot elevation in about 20 seconds (how did you measure rpm without out a rotor tach Larry?) With no blades attached, I see about 190 rpm meaning that is the maximum no-load speed for this motor and controller with this battery pack voltage and present gear reduction.  I did get a rotor tach that I have initially/temporarily installed.

The conclusion of all this is that it should be possible to add a second motor (and higher capacity controller?) or more powerful motor with half the speed reduction to prerotate to close to flight rotor rpm to minimize takeoff roll.

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This page contains a single entry by Cavlon News published on September 13, 2012 8:12 AM.

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