how do you tell when your motor's going bad - RC Groups
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Jun 03, 2002, 09:49 AM
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how do you tell when your motor's going bad

I was flying my soarstar with the stock motor over the weekend, and on the first flight with the second battery I started to get some surging in the motor. I noticed this during a low and slow fly-by at 15 feet off the ground 20 yards away from me, at about 1/4 throttle. The effect was almost as if I had punched the throttle a little and then released. Instantly I became worried and went around and landed. Since a soccer team was arriving anyway to use the field, I figured it was about time to go home. I'm pretty sure it was not radio interference.

Is this anything to worry about? If so, what should I be worrying about? What are the symptoms of a motor wearing out? (This is the second season I've used the motor right out of the box and I have never done any maintenance, break-in etc.)

Hopefully someone can help.
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Jun 03, 2002, 09:57 AM
Registered User
How old is the motor? Sounds like a glitch maybe? Have you ever put some oil on it?
Jun 03, 2002, 12:02 PM
Registered User

how old is the motor

It's a year old, with light usage by most standards (ie I don't fly it that often). No oil's ever been put it in.
Jun 03, 2002, 03:17 PM
soft yummy goodness.
freq's Avatar
Timing is probably about right for the Speed 400's life expectancy in this appication. Mine don't last nearly as long in a Zagi with higher current draw.

Speed change could be related to bushing or brush wear. As the brushes wear down, they can create more sparking which can also lead to radio glitching.

Horizon Hobby used to sell a replacement motor complete with gearbox for around $20, but I can't find it on their site today. Strange as it was there a few weeks ago. If your gearbox is fine (keep it greased and ballbearings oiled), you could just replace the motor with any $8 6V Speed400.

Jun 03, 2002, 08:28 PM
Registered User
I agree with freq. After a year,,it's probably had it. You might want to try some electric motor cleaner. It's what the car/truck guys use to clean their electric race motors. Your LHS should have plenty. Give that a try, that may help.
Jun 04, 2002, 01:01 AM
Registered User


When i had my ESC fry, someone said it may be the motor. They said to check resistance, which I measured and it was 0.3 ohms, measured on the 200 scale. I checked my new (never used) Graupner motor. It was about 33. Figured motor was bad and replaced. I soldered wires to the new motor, and the capacitor from pole to pole from the old motor, and started break-in. Measured ohms before break-in and was still at about 30. After 15 minutes on a single d cell, the ohms are down to .3

Is this an indictation of a problem? Should I be worried about plugging my new ESC into this new motor now? Is my old motor still ok?

Anyone know if resistance is a way to check for motor problems?


Jun 04, 2002, 03:00 PM
Registered User

which electricity meter?

Thanks for the input everyone. I'll look at getting a replacement motor. In the meantime, I'll try to test the ESC. Does anyone have any recommendations on the electronics meters for this (or other issues)? I see the posts recommending chargers are all over the board, but maybe there is some consensus here.
Jun 04, 2002, 05:40 PM
soft yummy goodness.
freq's Avatar
Ah ha! Finally found the SFM direct replacement for the Soarstar. Horizon Hobby part # SFM2032 $18. Includes motor & 1.85:1 gearbox.

Jun 04, 2002, 06:11 PM
Registered User
What often happens with these 380 & 550 Mabuchi style motors is that the brushes wear down so far that the spring arm can no longer hold enough tension on the commutator to make a good enough connection for the high currents we fliers tend to need.

I don't know if that's your problem for certain, but I have experienced the same "surging", and it was due to brush wear. The brush wasn't completely gone, just so thin that it wouldn't make good contact at the lower spring pressure.

You could upgrade to something with replaceable brushes, and those motors tend to have more consistent spring pressure as the brush wears. But at one motor per year, you're not doing bad.
Sep 23, 2002, 07:53 PM
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stevem1928's Avatar
you could just replace the motor with any $8 6V Speed400.
Where do you get the $8 motors?
Sep 23, 2002, 10:21 PM
burning holes in the sky
jjs63james's Avatar
Here is a Great place to get sp 400 zagi motors !
$7.99 Can. funds

just type in ghp013 into the search box.