bad motor or bad battery - RC Groups
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May 12, 2005, 08:49 PM
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bad motor or bad battery

Ihave just got a parkzone J3 cub and flew it into a tree.i got it out .\,and tried to fly again unsuccessfully.have tied several times but the red wire on the moter came loose and i soldered it back on.Now with a fully charged will only run full throttle for a minite or so then go off and then only run 1/2 full .It seems like the bat will not hold a it possible that i got the motor too hot while soldering the wire back on or that i have a bad battery pack.I am very new to the hobby "1 week"any suggestions would be appreicated.
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May 12, 2005, 11:03 PM
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Not sure where to start but here goes, since you had to solder a wire back on to the motor I'm guessing you hit pretty hard, which could have caused internal damage to the motor as well( been there done that). this could be your trouble & I would think most likley. Is it possible your solder job is making contact with the motor case? This could also be giving you trouble. Unless you used a lot of heat when soldering I don't think this is likely to have caused you trouble with over heating the motor. Does you prop spin freely & or did you bend the prop shaft? If prop isn't spinnng freely this could be adding stress to the motor, drawing harder( more amps) on your batt. Once when I had crashed my cub the motor would run but the servos were gittering constantly, pulled motor wires everything was fine. Replaced motor, all was well.
I doubt that your batt is bad but of course it is possible. Do you have a battery that wasn't in the crash to compair with the one that was in the plane? If so, & it gives that same results when you run the motor, as the one that was crashed I would replace the motor. If you have a volt meter check to be sure your getting a full 8.4 volts on your fresh batteries. You could also remove the prop run the motor & mesure the voltage at the motor terminals to see your 8 volts, if you have full voltage & it slows down , new motor! Granted you won't have any load on the motor without the prop but that should allow the motor to run longer further proving the motor bad if it slows down in such a short time.
I can't remember what my amps were but I think I was pulling around 5 amps at full throttle, someone correct me if I'm off on this, so if you can measure your amps you would want to be in the area amp wise with the prop on. If it starts to go up or it's considerably higher, new motor.

This about does it for my 2 cents. I'm sure others will be able to give some insight.
May 14, 2005, 11:22 AM
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scratchandbash's Avatar
Sometimes the front bronze bushing of the motor gets pushed in on impact, causing high friction resistance inside the motor, thus power loss. I've done this, and lightly tapped the shaft from the rear, which pushed the bushing back in place. Just a thought.
May 14, 2005, 04:11 PM
Registered User
thanks guys

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