To interlock or not to interlock

Hi guys,

With the new 5-point throttle curve, as I understood, we only need a switch on channel eight for throttle on and off and the fw will take care of the rest.
But, do we still need to have an interlock switch?
Or is it a good safety option?

yes, we do for an autopilot. I call it throttle hold, which is the standard terminology in RC heli’s since the beginning of time, and which most heli users/pilot understand. It is, in effect, the fuel shutoff for the engine in your helicopter to prevent an unwanted start when working around a machine with the rest of the flight systems active (flight controller armed).

It serves the purpose of being able to idle the engine for autorotation practice. It allows ramping the throttle to smoothly engage the clutch so you can have a ground-idle rotors turning setting on the bottom of your throttle curve. When using switch arming it allows idling the engine with clutch disengaged for cooldown, as shown here where I am demonstrating switch arming (vs the weird rudder input thing which I think DJI invented for multi’s back in the day). I take off using just the throttle curve, which advances very smoothly to takeoff power, then engage the governor in hover.

With the combination of the throttle hold, throttle curve and H_RSC_IDLE setting it prevents having to use throttle trim to idle a combustion engine, as is normal with most FBL setups - can all be done with switches.

So since throttle hold has been a staple in RC heli’s since they were invented, we’re not going to change it anytime soon.


Thanks for the detailed explanation!
I actually didn’t mean to drop interlock from ArduCopter, my question was should I set it up with my heli.
I am familiar with throtle hold as I am using it on every quad/heli I’ve setup.
But, nevertheless you put some light on the use of it I was not familiar with as I am an electric guy only :sunglasses:. I am planning to switch to gas helis in the future but still have to learn a lot about helis as for now I only managed to destroy (and rebuild) them, not fly them :grin:

And thanks for mentioning the arm by switch, I completelly forgot about it.

Funny thing, I have my heli setup with Pixhawk 1 and had to deal with the interlock for a while until I figured out, but now i’m testing the Pixhawk 2.1 alone and haven’t seen the interlock message not once. Both board are running arducopter 3.5.5 with trad heli frame type.

I’m attaching both parameters files:
Xcell 99SE Electric v2.param (13.5 KB)
Pixhawk 21 Trad Heli testboard.param (13.6 KB)