Hello,
My Picolario telemetry system has just saved the third plane.
For those who dont know, my HKM ASW-27 has a nose-mounted electric motor. Today I was trying for the first time, a Kontronik Fun 500 motor with 5.2:1 gearbox, 14 x 7 folding prop, and 16 x RC2400 pack. The circuit from the motor to speed controller to battery is straight and the wires are just long enough.
An ACT "Powerbooster 24" BEC is spliced into the drive battery side of the speed controller and provides power to the Rx and servos. A 4-cell 500AR backup battery is connected to the Rx and servos through a separate circuit.
During the second flight with this motor/prop/battery combo, a couple of climbs to altitude went normally. A few radio glitches hit the Rx but they were intermittent and did not seem to be life-threatening. Glitches cause the telemetry to make a unique sound and can cause a momentary low-voltage warning.
Following the minor glitches, the telemetry indicated that the voltage on the Rx was continuing down, where I would expect it to stay constant due to the BEC. I brought the plane lower for observation, then tried to run the motor, but it was wouldnt run. Landed safely.
Post-landing, I found that the motor had unscrewed from the gearbox, twisting the motor and controller wires, and had UNPLUGGING the drive battery. This disabled the motor and the BEC, so the Rx and servos were powered only by the 500mah backup battery.
The Kontronik Fun 500 does not have mechanical lock on the gearbox thread. With a normal folding tractor prop, the torque of the motor tends to unscrew the gearbox. The torque which tends to unscrew the motor from the gearbox is the sum of the motor shaft output torque and the reaction caused by accelerating the commutator. The gearbox was relatively dry, so maybe the lack of grease caused extra vibration which helped to loosen it. The motor/gearbox was noisier than I would expect.
Lessons Learned: Lock threaded gearboxes. Picolario telemetry and independently-wired backup batteries saves airplanes
Rgds, Jimmy
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