Hi,
I have just built an RC switch circuit that drives a relay, which is controlled by a Futaba transmitter and receiver.

The switch itself operates fine with a throw of the 6th channel switch, switching the relay on and off.

But when a servo on any other of the 5 channels is operated it interferes with this circuit causing the relay to switch rapidly between states.

Could this be something to do with the servos current draw?, but then again the 6v powering the receiver is regulated.

It appears that a servo being operated sends a spike through the switch circuit causing the output of the 4013(pin 12) to go high, yes/no?

Does anybody know of a way to eradicate this problem?

Thanks for your time.
NM
(Circuit Fig A)

 

If your power supply is not capable of powering the motor it shuts off or current limit its output to a lower value as not to burn out. Check if your power supply is able to power the motor. What the rating voltage and current of the motor? What is the stall current of your motor? What is the power of your power supply?

Connect a large electrolitic capacitor in parallel with the motor to see if it solves your problem.

 

Mik3,
Thanks for your help, a 220uF cap across the motor terminals solved the problem!

Although I thought this would have been taken into account when the servo itself was designed.

Regards NM