Weird .....

[Larry Dudeck]

Here is a question for you EE types.

In the process of mounting a gear box I needed to shorten the motor shaft of a S400 motor. My first attempt was to use a metal file.

With the motor mounted on the plane, I ran the motor at three or four thousand RPM. As soon as the metal file touched the motor shaft all four servos began to cycle through their entire range. Move the file away, servo movement stopped.

This didn't look like a very good idea so I quit.

My question to you is 'what was going on'?. Obviously the file and the motor shaft was generating a lot of RF interference that overwhelmed the receiver.

BTW, my Dremel with a cut-off disc made short work of shaft shortening.

(Can you say 'short work of shaft shortening' fast, five times?):D :D :D

[Norman Adlam]

Larry,

Metal - to metal contact is a well known way of generating local electrical interference, as you've discovered! :)

That's why people are warned abot potentionally noisy servo / horn etc connectors.

'course I can say 'short work of shaft shortening fast, five times' - there, I just did it! :D

(keep taking the tablets!)

Cheers,

[BMatthews]

Any spark you can make has radio frequency emmisions that will do a real number on your radio over a short range like this.

I suspect some of the field leakage from the motor was inducing some voltage into the file or motor shaft and when you touched the file to the shaft there were some sparks. That may be all that was needed but with you acting as an antenna by holding the file there was probably also a much more closed in path for the RF energy to couple to the reciever antenna.

Eliminating or at least damping out the RF energy of the sparks is why the motors use the capacitors of course. You just found another way to mess things up that bypasses the caps.... :D

[Mr.RC-CAM]

From what I understand, intermittant metal to metal electrical contact near the Rx antenna causes minute phase shifts in the airborne RF signal. This results in confusing the Rx's demodulator.

Any metal-to-metal make/break contact next to the R/C Rx is prone to do that. In this case, the file was just another spin on this. ;)

RC-CAM

[BMatthews]

Yes any metal in proximity to the antenna becomes part of the antenna system and intermittent "retuning" by mechanically varying it's configuration like that could cause stuff like this to happen. In this case with the motor running I suspect it's more likely to be electrical noise than any distortion to the recieved signal. The way to tell would be to stroke the file over the shaft without any power going through the motor. If it still caused glitches in the radio then it's the RF distortion. If there's no effect but it comes back with the motor running then it's electrical noise.

But then again RF is a little bit of black magic sometimes. Good call.

[Sparky Paul]

I can't believe you guys haven't seen your servos jump when you attach the Nicad to the glow plug! :D

[Larry Dudeck]

glo plug??????