Motor arming and kill switch

Mike Shellim 26 April 2016
Updated 3 Oct 2021

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

Operation

To arm the motor:

1. Throttle to idle
2. Elevator stick back
3. Pull SH

To kill the motor:

• Pull SH for 2 secs

How it works

The system is based on the safety switch recipe with a couple of mods.

• L3 is the arming switch. It's a Sticky switch. It's set by the arming gesture (L1), and reset by the disarm gesture (L5).
• L1 is the arming gesture: throttle to idle + elevator fully back + pull SH.
• L4 and L5 handle the disarming gesture:
  • L4 is true while SH is pulled, not while arming ('AND !L1') .
  • L5 goes True briefly, after L4 has been true for 2 seconds.

Note: in L01 and L02, 'Thr' and 'Ele' refer to sticks (not inputs) - make sure to make the correct selection (inputs are prefixed with 'I', sticks have no prefix)

Integrating in your setup

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

How it works:

• The first line sets the motor to motor off. This is the default state.
• The second line activates the throttle lever. It over-rides (multiplex=REPLACE) the first line when the motor is armed (L3=True).

[An alternative method of disarming the motor is via the Channel Override special function. However, this method is not recommended as it is applied after the mixer values are calculated. This can cause problems for example if you want to query the mixer value to detect if the motor is running. The method shown above is more explicit and easier to debug.]

Download demo

Customisation

The solution presented here is very safe, but cannot be used for in flight rearming. However you can substitute your own gestures for L3 and L5, to achieve the desired balance between safety and convenience.

Safety first!

• Remember to set the failsafe, so motor goes to idle on loss of signal
• Use the channel monitor to test operation before connecting up the motor