Motor arming and kill switch

Mike Shellim 26 April 2016
Updated 18 Feb 2021

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!

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:

• Pull SH for a minimum duration (user settable), and release.

How it works

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

• L1 is the arming gesture: throttle to idle +elevator fully back + pull SH.
• L4 is true while SH is pulled, but not while arming ('!L1') .
• L5 is the disarm gesture. It generates a True pulse after L4 has been true for 2 seconds. In other words, after pulling SH for 2 seconds, not while arming.
• L3 is the arming switch. It's set by the arming gesture (L1), and reset by the disarm gesture (L5). Use this to control the motor's state (idle/running).

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 motor mixer output to detect if the motor is running. The method shown above is more explicit and easier to debug.]

Download demo

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