[Paul Hamilton]

Reactor 35" EP with Electrifly Rimfire 35-36-1200kv, Electrifly silver series 45A ESC, Turnigy 40-50C 2200mah and APC 11x7 electric prop. First lipo electric plane. Awsome performance similar to .15 nitro. 4th flight motor stops. On the ground advancing the throttle gives 1/2 sec burst and motor stops. Disassembled motor and two of the windings have been hot and melted some of the insulation. Reassembled motor and after several 1/2 sec bursts the motor is very hot. The motor is cooked?? How do I tell if the ESC is also damaged?? Is the prop too big for this setup

[philipa_240sx]

Paul,

You never mentioned the number of cells?

Although I have never used the Rimfire series, Dr. Kiwi on RCG has done some testing and found GP's prop recommendations and ratings to be overly optimistic for this motor. He tested the 1000Kv version of this motor and found that a 10x5 on 4S and 11x7 on 3S was the max for continuous operation. At 1200Kv, the prop sizes would have to be even smaller!

The general rule of thumb is 3W/gram (motor weight) continuous. It's a simple calculation purely based on the maximum amount of heat dissipation without melting the windings.

Great Planes recommendations for this motor is an astounding 500W continuous:

500W/102g = 4.9W/g

This is way over 3W/g and I would be very impressed if the motor could sustain this for any prolonged period of time!

Anyways, back to your problem...

I can almost certainly say this motor is over propped. Dr. Kiwi's tests prove GP's prop recommendations are way too big. Although he did not test the 1200Kv version, it's likely that a 10" prop on 3S or 9" on 4S is the biggest you can run.

As for the ESC, depends how bad it the damage to the motor was. If the windings shorted it's possible the FET's on the ESC are cooked as well. The only way to know for sure is to test on a known good motor.

Finally,

The most valuable tool when it comes to electrics is a Watt Meter. Without one, you are just guessing. But even without one, a simple static test (60sec continuous operation) and checking motor temps is decent indicator if you are over propping. The motor case should never get above 50degC or so. Oh, and be careful... unplug the motor and use a thermometer (ie digital meat thermometer) to avoid burns!

[Paul Hamilton]

The battery was a 4s 2200mah 14.8v When comparing the prop size to those recommended on the motors at HOBBY KING it seems the 11x7 is way too big!! I must get a watt meter. Thanks for the info

[philipa_240sx]

Originally Posted by Paul Hamilton

I must get a watt meter. Thanks for the info

Some cheaper watt meters use resistance shunts with questionable accuracy. The better ones use hall effect sensors. A few recommendations for quality watt meters:

Available from Hobbyking:
- RCElectronics WattsUp
- AEO-RC P1 Meter (Hobbyking X1)

Locally available in Canada:
- Bantam e-Station - from RCFlightStore
- Astroflight Wattmeter - from Great Hobbies

And at the more expensive end of the scale:
- Eagletree eLogger
- Hyperion E-meter

[philipa_240sx]

Originally Posted by Paul Hamilton

The battery was a 4s 2200mah 14.8v

From the GP Reactor Bipe Manual:

Motor & Propeller Recommendation
- Great Planes RimFire™ 35-36-1200kV Brushless Out-runner Motor (GPMG4620)
- APC 11" x 7" TE Thin Electric Propeller (APCQ4128 ) recommended(draws 34 amps max.)

The Reactor Bipe EP has been tested with 11.1V LiPo packs
ranging from 1200mAh to 2100mAh.

And there is the answer to your problem... the 11x7 prop is recommended with a 3S (11.1V) lipo. If you went down a prop size (say 10x5 or 10x7), the 4S pack probably would have worked.

Now that you are in the market for a replacement motor, you should look at the Motrolfly series from Subsonic Planes:

http://www.subsonicplanes.com/Motrolfly_Motors.html

Something like the DM2810-830 with an 11x7 or 11x.8.5 prop (4S) would give you tons of power. Drop Ken Young a line at Subsonic Planes: subsonicplanes@yahoo.com He'll set you up with a great motor. I've purchased several motors from him and they are very good for the price. Plus Ken backs up his products with great service.