Rc kill switch for gas engines

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      A RC kill switch is basically a cut off switch of a gas engine ignition operated via the radio transmiter (TX). The idea is that the engine’s ignition kill switch it’s safer to be on the TX than on the model itself. Of course the engine can be killed by the throttle trim but it’s not 100% guarantied if the servo or the connection rod fails. The switch itself may be mechanical (analog) or electronic (optical).

      Mechanical switch

      A mechanical kill switch consists of a servo (it can be a once-crashed servo that isn’t quite control surface trustworthy) and a micro switch.

      The mechanical setup with a servo and a micro switch is still popular among pilots which are still using magneto equipped engines such as Zenoah G 62 SL.

       It has some disadvantages such as:

           1. Possible servo failure.

           2. Minor interference (glitches) to receiver due to moving parts of the micro switch.

           3. Inability to kill the engine in case something goes wrong with the receiver’s (RX) power supply.

      Optical on/off switch

      The optical on/off switch is handy in case something happens and you need to kill the engine remotely. For example, the throttle servo fails or the throttle gets stuck somehow with the engine running. Worse scenario is having the engine stuck at a fast idle, too fast to land and too slow to fly. It is really impossible to reach up there as the plane flies by to try to flip the switch! Several brand names kill switches are available in the market today such as:  

      The optical on/off switch has the advantage to automatically kill the ignition when the RX is off, so you can, even if your RX has a wrong failsafe and is non-responsive (that would be your own programming error by the way, but never mind) to kill the engine by just switching off your RX. Mechanically operated kill switch, will not kill your engine in case something goes wrong with the RX power supply, but the optical switch WILL.

Opto Gas Kill Switch - Rc Kavala Acro Team

By a kill switch here

      It is equipped with an indication led for armed ignition, preventing you from a full afternoon of fruitlessly hitting the propeller! Plug in the unit to an AUX channel on the TX. Then hook up the power in line to the battery and the power out line to the CDI module.


      Then when the Radio is up and running, toggling a switch on the TX turns the CDI unit on or off. Since it is optically isolated any RFI on the wires going to the RX are kept to a minimum.

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This Post Has 4 Comments

  1. chuck

    i am building the 123 inch B-25 J and have two r/c gas motors with electronic ignitions and two cut off switches..can I wire them in parrallel….
    thanks again;
    chuck s.
    j3cub43@yahoo.com

    1. Dimitrios Katsoulis

      Hi Chuck
      Logically you can connect the kill switces in parallel. It does not make any difference if they are supplied by one battery or two separate ones. The receiver will simply send the on/off signal to both the internal electronic circuits.
      We wish you success with your giant B-25J!

  2. Dave

    Hi all,
    I built a rc lawn mower due to physical issus. I was able to use a rc relay to turn on and off power to the motor relay. Even the failsafe works. I tride a Battleswitch that cost almost 4x what I paid for the “oversea” relay and the wires tried in SC and S2. SC and S1 would trip when main power was turned on. Nothing would trigger with SC and S2. I place the relay between the main switch load to the hot side of the 120amp relay for controller. Now i want to kill (ground) the lawn mower engine coil ground with a relay. I wave another relay and a optical kill relay. It has the RX plug a power in and out. The RX has it own trans 5v power supply. Been staring at the power lead thinking how to wire it to keep the grnd circuit open for run then close it via TX to kill the engine. Ive also thinking of playing with a relay that keeps the circuit open with power or closes with power loss. This is a little off but i do fly drones.

  3. Dave

    Hi all,
    I built a rc lawn mower due to physical issus. I was able to use a rc relay to turn on and off power to the motor relay. Even the failsafe works. I tride a Battleswitch that cost almost 4x what I paid for the “oversea” relay and the wires tried in SC and S2. SC and S1 would trip when main power was turned on. Nothing would trigger with SC and S2. I place the relay between the main switch load to the hot side of the 120amp relay for controller. Now i want to kill (ground) the lawn mower engine coil ground with a relay. I have another relay and a Rcexl optical kill relay. It has the RX plug a power in and out . The RX has it own trans 5v power supply. Been staring at the power lead thinking how to wire it to keep the grnd circuit open for run then close it via TX to kill the engine. Ive also thinking of playing with a relay that keeps the circuit open with power or closes with power loss. This is a little off but i do fly drones.

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