Weird motor malfunction

[Sauerbrey]

Hi there,

I recently build the Flite Test Tiny Trainer. I put on the electronic components from another plane I had laying around and everything worked like a charm.

I wanted to maiden my new plane yesterday, but minutes before my first flight with the model I encountered a weird malfunction with my motor:

As soon as I throttle up the motor begins to turns for half a second in one direction, comes to an abrupt halt and turns the other direction, it keeps doing that until I cut the throttle. I tried changing the direction of the motor by changing the cables which unfortunately didnt help.

Can anybody help me with my problem? I suspect my ESC is malfunctioning but you have much more experience in this matter than I do.

Here are my specs:
Spektrum DX61
ESC: Hobbywing Skywalker 40A
Motor. Brushless Motor
Battery: 950mAh 2 Cell
Receiver: Spektrum S603

Thanks for the help and have a nice day
Georg

 

[Merv]

...As soon as I throttle up the motor begins to turns for half a second in one direction, comes to an abrupt halt and turns the other direction, it keeps doing that until I cut the throttle...

That stuttering behavior is typically of a broken connection between the motor & ESC. First check for a bad solder joint, gently tug on each of the bullet connectors, if one is only held by the heat shrink, it will easily come off. If all of your solder joints are good, look for a broken wire somewhere between the motor & ESC. One way is to unplug one of the 3 wires at a time. If the motor behaves the same, that’s the wire with the break. If you can solder, it’s an easy fix. I’ve done it many times.

The other possibility, one leg of the ESC has failed, I suppose it could be fixed, if one had the electronic skills. I have always chosen to replace the ESC rather than attempting a repair.

 

[quorneng]

Sauebrey
rSuch motor behaviour s caused by a broken connection on one of the three motor wires.
To start a brushless motor the ESC give a strong pulse to a pair of the wires. This makes the motor jump which causes a small voltage to be generated in the third wire. By measuring that voltage the ESC can determine which way the motor moved and organises the next pulse in next wire pair to start and continue the correct rotation.

Now is one of the wires is broken the ESC cannot "read" the third wire voltage so it just sends another pulse, hence the motor tends to just jump backwards and forwards. It will never run unless the bad connection can be rectified. Incidentally these starting pulses are at full power so the ESC is likely to quickly over heat and itself get damaged if you leave the motor jumping for too long.

As Merv suggests check the wiring to the motor very carefully, including any solder joints. However if the fault is a broken wire inside the motor or a component failure in the ESC then replacement is the only practical option.

 

[Sauerbrey]

@Merv, @quorneng Thank you so much! I resoderd the connections and it worked again