Hello. I am planning to use Ardupilot for a custom aircraft launched from a device at 400’ altitude. this aircraft would need to be able to autonomously return to a specific site once launched, and I am unsure if I will be able to reliably communicate to the UAV for the MAV commands in order to arm the drone using an RFD900. we are using either a Matek H750 or a Cube Orange Flight controller. Is there a way wherein, one might be able to set the home location for the drone, and DELAY the activation of the failsafe override using an electrical signal of some sort?
Throw mode: drop might be able to do the arming, and Rally points could be the next thing…
The RFD900s will have extreme range if unobstructed and the air unit has plenty of altitude. What range are you hoping to get?
my concern with Throw mode is the throwing lol. The Drone will be mounted atop a rocket going Mach 1.7 up to 30K feet, deploying at 400’ on descent and descending at 10m/s or 10 ft/s (i gotta check) under the main chute. were trying to get a max range of 6 Miles out of the drone. I’m worried the impulse of the ignition or the parachute deployment would trigger the throwmode into thinking hey start the motor! while inside our deployment housing. so theres relatively nothing out where this will be launched, (although i have seen planes blow through the TFR lol), so im not too concerned with the range, rather them disconnecting for some reason. If the RFD’s reconnect fast enough after the launch, i can imagine a mission where at 400’ we trigger the deployer and launch the drone and then set an event for the drone to start the return mission at 390’? my concern is the timing of that and again, the motor starting inside the housing.
The RFD’s shouldn’t disconnect unless there’s extreme electrical/RF noise, or you can outrun the radio signals propagation 
You will probably have to test.
Throw mode may work for this use case, it’s been tested before dropping a Paramotor from a Paraglider. Another possibility that isn’t in Copter at present but it is in Rover is a Switch Start feature with a parameter for it (AUTO_TRIGGER_PIN). You could use an electrical signal to close a contact. But, it’s not in Copter or Plane.
So I read into it. and my precursory look seems to suggest that its only available in copter mode? I’m still new to Ardupilot as a whole, but am I able to take things from copter or rover and throw them into plane mode? Were a ‘standard’ fixed wing, just sans the fixed and more deploying wings, better range for a 2.2lb plane than a 2.2lb quad.
Throw Mode is in Copter, switch start is in Rover and w/o developement they are not available in Plane. Plane has other Auto Start options but not sure they would suit your use case. Perhaps you need more sophistication with Scripts or a Companion Computer.
@Awesome4rbiter Feel free to post this question or link to this post in the Discord chat. There is another user who is doing glider rocket launches from the ground.
Plane Channel: ArduPilot
This sounds like something where a custom Lua script might nice.
Maybe one of the checks for “I am in the housing. Don’t start the rocket” could use a short range rangefinder? You will probably want some redundancy on the don’t start the rocket check either way.
awesome thanks! I will post a link to this there. redundancy would be nice for this lol. its more a check on the don’t start the drone. The rocket I have no control over, were just along for the ride on that until its our time to shine.
Oh for some reason I thought you had a rocket on your glider to help exit the housing.
were using a spring launch or other electrically triggered event inside the payload housing (were still designing that). Were atop a big ol solid rocket until 30K feet. then we get pulled out by the parachutes, and at 400’ we launch from the payload housing dangling below a chute.
Any specific reason you are leaving the deployment from the rocket till so late? Where is the 400’ constraint coming in? Project related or personal choice? The choice of main deployment height depends on many factors, including the sink rate under drogue. I see this low deployment a lot and question the rationale. Personally I do dual-deployment flights and deploy the main chute at 2000’. That means I have lots more air time to get a packet back to base with the location, and also if the drogue failed to deploy the main can pull up the ballistic rocket successfully before negative altitude is an issue. With deployment at 400’ you are asking for trouble IMHO. Remember to design for off-nominal situations, not just nominal 
Whatever you do think through all the safety aspects.
the competition were entering has a restriction for 400’ for any UAV payload deployment height. thats set by the hosts, my guess is that they don’t want to deal with the FAA for drone shtuff is my guess, I was originally going to go through the FSDO in order to try to get approval in order deploy at apogee (try to claim the world record for highest altitude RC airplane while at it), but it would have been quite a bit of extra work to justify the safety fof the drone to the FAA. So this is a collegiate project at Cal Poly Pomona. I’m not part of the Avionics and Recovery team. they handle all of the parachute equipment. They also have a secondary GPS for the rocket itself, so its not reliant on the drone in anyway. out drogue deploys at apogee or shortly thereafter, and main deploys between 1000-1500 in order to prevent drifting too far from the launch site. our payload bay comes out below the main.
Thanks for the additional info. I thought you might have had external constraints on that. Just remember to think of off-nominal situations when you are designing the entire system.
FYI, I am a L3 Tripoli Rocketry Association member with some decent projects under my belt.
I wish your team all the best for the competition. Have fun and good luck .
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