FMS Weak Motor Issue Yak 54 1300mm

[jeff]

Anyone else have the FMS 1300mm Yak 54? the 3948 760kv motor spins smooth and true, when cold but in flight, seems very weak, the plane flies slow and must be flown at full throttle, for all but landing. After a 6 min flight it is not very warm but does not spin freely, as it does before the flight. A guy at my local hobby shop said that not spinning freely after a flight, is normal, but I don't get that from my Rimfire 32, or the motor on my flyzone Sensei motor.
Would like to replace the 3 blade prop, but the prop adapter has the odd ball, hex block on it. Any help?

[Konrad]

RE: FMS Weak Motor Issue Yak 54 1300mm

How old are the batteries? Are you getting good voltage to the motor (ESC) under load?

Not spinning easily after a flight is NOT an indication of a problem. It usually means that some capacitor in the ESC is staying charged keeping the mosfet (special transistor) on, effectively shorting a motor winding. After about 5 minutes the Cap will self discharge and the motor will spin freely. If there was drag or an electrical problem with the motor it would he hot! RimFire 32? What I think you are seeing is a result of the ESC not the motor. This is normal with many ESC. Keeping a motor wind shorted cause electrical drag when you try to spin it. The motor is acting like a generator.

The hex drive is a good thing as it keeps the spinner and prop from slipping. You can use some washers with a 9mm hole to shim above the hex. Or ream (not drill) a 9mm hole in your replacement spinner and prop to allow them to pilot on the points of the hex. Always like 2 bladed prop for performance. I don't understand the idea of 3 and 4 bladed flying props. I cant see the blades in the air.

Try this on a loose motor, maybe the RimFire 32. Hold all three wires together in you hand or with some bare wire. Then try to spin the motor. You will notice that it is much harder to spin. This is what the mosfets are doing, tying the motor leads together.