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Please help diagnose motor problem.

Please help diagnose motor problem.

Old 07-28-2012, 06:17 PM
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Default Please help diagnose motor problem.

A friend was running his RTR SC10 today. Stock brushed motor running with 5000mah 40c 2s lipo. He's put less than 10 batteries through this motor. While running today, it seemed to be running OK until he hit some pipe and tried to backup, it had completely died. We tried multiple batteries, motor appeared dead.

He took it apart and blew it out with a air hose, every looked OK. He got it back together and it still isn't turning. Once we did some testing with a multimeter, a AA battery and a NiCD, here's what we were able to find:

- With the motor out of the truck, he touches the connectors to the appropriate ends of a AA battery. The motor turns.
- When he touches the connectors to the appropriate ends of the NiCD battery, the motor turns.
- With the motor disconnected from the ESC and using a multimeter to test the voltage coming out of the ESC, idle reads around 0.5v and up to full throttle reads almost 17v. Going from idle to full gives the appropriate voltage increase.

However, as soon as we connect the motor to the ESC, we get nothing. I get no voltage read from where they connect. These are the normal bullet connectors on RTR vehicles. It's like as soon as they are connected, the ESC decides it doesn't want to output anything. The lights on the ESC still light accordingly (i.e. green for throttle, red for brake, dim amber at idle).

Can anyone tell me what's going on with this?
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Old 07-28-2012, 08:16 PM
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Connect the motor to the ESC and re-test for voltage at various throttle positions. I highly suspect the ESC to be the culprit and if my suspicions are correct, you will have no voltage when a load is introduced to the circuit.
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Old 07-28-2012, 08:21 PM
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what is the esc?
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Old 07-28-2012, 08:21 PM
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Originally Posted by SolderGlob View Post
Connect the motor to the ESC and re-test for voltage at various throttle positions. I highly suspect the ESC to be the culprit and if my suspicions are correct, you will have no voltage when a load is introduced to the circuit.
This is correct, there is absolutely zero voltage reading anywhere in the throttle range or at idle as soon as the motor is connected to the ESC. Without the motor connected, I get voltage reading from the ESC. Plug in the motor and nothing and it's like the ESC just dies.

What would cause it to do this? Just seems weird it will output voltage and then once it sees the motor, says "hell no".
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Old 07-28-2012, 08:22 PM
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Originally Posted by vw addict View Post
what is the esc?
Couldn't tell you now, I've left my buddy's house and it's a little too late to send him a text to find out. It is the standard SC10 RTR ESC, though.
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Old 07-28-2012, 08:24 PM
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Without getting too technical; the current source in the ESC has failed.
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Old 07-28-2012, 08:25 PM
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Originally Posted by SolderGlob View Post
Without getting too technical; the current source in the ESC has failed.
You sound very confident, I'll research this, thank you.
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Old 07-28-2012, 08:27 PM
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Originally Posted by blurredvision View Post
You sound very confident, I'll research this, thank you.
I would contact A/E customer service
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Old 07-28-2012, 08:41 PM
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Originally Posted by vw addict View Post
I would contact A/E customer service
He will be, definitely. I just like to learn about this stuff, plus this particular problem just seemed very odd.

Thanks all.
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