Posted by Jason Hilton on October 15, 2012 at 9:33pm
Hi,I finally completed and configured my 3dr-c quad full kit (880kv motors). About 5 minutes into my (very stable!) first flight, the quad unexpectedly flipped over and hit the ground. I killed the throttle when it happened, and I was very low so didn't sustain any damage. After some diagnosis, I found that one of the motors was twitching back and forth when under throttle. At first it went away, but I continued to bench test (this all happened today) and now the motor only twitches.I have tested the following:-I have ruled out it begin the PDB by swapping another ESC to the side that the problem is occurring-I also ruled out bad bullet connectors by soldering the wires directly, the problem persists-I switched the ESC to a different motor and it did not turn (there is a possibility it was a connection issue when connected to a confirmed good motor, I had already soldered in and had to use test leads to connect to the second motor)-I switched the motor to a different ESC and it continued to twitchIs it possible I received both a bad motor and a bad ESC? I'm certain the motor is bad as it behaves the same regardless of the ESC it's connected to. The ESC may have issues, but I can't be certain.
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The wires of most mainstream hobby brushless motors are very poorly supported as they go into the bell housing (normally just a small piece of heatshrink). It's very easy to have a wire break or short inside that housing, which will show up as a stuttering motor.
I now always put a small dab of epoxy to try stabilise the wires of any new motor. As you've checked the motor with a different ESC I'd suspect that's it is probably one of those internal wires. I have been able, on two motors, to carefully resolder the broken wire where the original solder had broken but the actual internal wires are lacquer coated it can be hard to get the solder to stick. Otherwise replacement is the only option unless you're keen to rewind the motor.
Replies
The wires of most mainstream hobby brushless motors are very poorly supported as they go into the bell housing (normally just a small piece of heatshrink). It's very easy to have a wire break or short inside that housing, which will show up as a stuttering motor.
I now always put a small dab of epoxy to try stabilise the wires of any new motor. As you've checked the motor with a different ESC I'd suspect that's it is probably one of those internal wires. I have been able, on two motors, to carefully resolder the broken wire where the original solder had broken but the actual internal wires are lacquer coated it can be hard to get the solder to stick. Otherwise replacement is the only option unless you're keen to rewind the motor.