Motor arming system

Mike Shellim 26 April 2016
Updated 11 November 2022

Motor arming is a common topic in the forums! Here's a recipe for a safe arming system. It's designed to protect the user from accidental spinups before and after the flight.

For this kind of system, (a) arming should be difficult, to avoid any chance of accidental spinups, and (b) disarming should be easy but not so easy that you can do it accidentallly whilst flying the model.

(Note: a kill switch is slightly different - it must offer an easy and quick way to stop the motor. If you want a kill switch, then the code can be modified quite easily).

The Sticky logical switch

Arming systems are typically based on a Sticky switch. Think of it as a customisable on/off switch. The Sticky switch is switched on via the arming gesture and switched off via the disarm gesture. The arming and disarming gestures are themselves implemented as logical switches.

This method provides a lot of flexibility, as you can customise the arming and disarming gestures independently.

Operation

For this example, we'll use the following gesture to arm the motor:

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

And to disarm the motor:

• Pull SH for 2 secs

The code

In the following code:

• L1 is the arming gesture: throttle to idle + elevator fully back + pull SH.
• L5 is the disarm gesture:
  • L5 goes True briefly, after L4 has been true for 2 seconds.
  • L4 is true while SH is pulled, but not while arming ('!L1').
• L3 is the arming switch. It's set to on via the V1 parameter (L1 in this case), and off via the V2 parameter (L5).

Note that '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

With the arming logic done, we can apply it to the motor channel:

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 if you need to query the motor mix output, for example to activate a dedicated flight mode when the motor is running. The method described in this article is also easier to debug, since all the code is contained within one menu.]

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