Here's a poser for you- motor runs with model switched off. - RC Groups
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May 05, 2002, 01:37 PM
Sloping off....
leccyflyer's Avatar

Here's a poser for you- motor runs with model switched off.


An old favourite electric model of mine developed a fault yesterday that had us all puzzled. It's a speed 400 glider-ish model, the Searching 400. This has a 6v Sp400, Robbe 6.5x4 folder, 7x500ARs, a Westbury 20 amp ESC and a Hitec Mi04 receiver. The Westbury is equipped with a BEC, an arming button and a receiver swith.

After completing a flight I went over to retreive the model. I switched off the receiver, then switched off my transmitter and carried the model back to the pits. On the way back to the pits the motor started to run intermittently at low speed, despite the radio being switched off. I switched the radio back on, TX first-then RX and everything functioned normally. Then switched the radio off again and the motor began to run intermittently again.

One idea was that that the receiver switch must be malfunctioning, but if that is the case the servos did not work, only the motor, also the arming button isn't performing any useful function. The alternative is that the ESC itself is broken and I shall replace that with a more modern unit now in any case, I was just curious if anyone else had experienced such a fault.

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May 05, 2002, 01:57 PM
Been There! Done That!
boomerace's Avatar
Aliens..... Spooks..... That's a new one. What had you guys been drinking? I'll have some.
May 05, 2002, 02:05 PM
Plane hugging cat
Vonbaron's Avatar
Yes Brian, I've experienced it with my RCLine 20A ESC.

I don't trust arming switches. They are not off switches. Safest way is to put a switch on the motor battery lead and leave the arming switch on.
May 06, 2002, 12:00 PM
Supersonic Engineering
GordonTarling's Avatar
Brian - the problem is probably due to the fact that the FET gates don't have pull-down resistors on them. When not being driven by whatever device is used to drive them, the gate voltage will 'float' and pick up any stray voltages that happen to be around. If you have easy access to the circuit board, a 10K pulldown resistor from drive FET gates to ground would probably do the trick.

May 06, 2002, 12:13 PM
Sloping off....
leccyflyer's Avatar
Thanks for the tips chaps.

I don't like arming buttons either, for me the model is considered live as soon as the battery is inserted.

I'll probably retire this one as it's a bit old and heavy for this model, a smaller, more modern unit would allow me to shed a bit of excess weight. It'll go to a good home though and maybe those resistors will find their way onto the circuit board there.