Motor arming and kill switch

Mike Shellim 26 April 2016
Updated 24 July 2017

Here's a recipe for a safe arming/kill switch for an electric motor. It's designed on the premise that arming the motor should be difficult, and killing it should be easy - but not so easy that you can do it accidentallly.

It's based on the safety switch recipe with a couple of mods.

Operation

To arm the motor:
  1. Throttle to idle
  2. Elevator stick back, and hold.
  3. Pull and release SH.
  4. Release stick

To kill the motor:

How it works

The system is implemented as a bunch of logical switches, see screenshot below. Key points:

Highlighted areas show differences from the safety switch recipe.

Usage

Here's the suggested mixer setup for controlling a motor on CH3:

How it works:

[Aside: an alternative method is to have the motor active by default, and use the Override special function to disable it. However, I don't recommended this. The Override function is applied at the last stage in the command pipeline, and has no effect on the raw channel outputs. This can cause problems if you reference the motor channel e.g. to detect if the motor is running. The method shown above is more explicit and easier to debug.]

The following demo shows the arming/kill switch operating on CH3.

MotorArmKill.zip

Safety!