I have been doing some testing (outside the US) that involve very high altitudes - 1800 meters or more. The climb takes no more power than coming down. Even though going up takes more power per minute, coming down is slower, so the total power consumed when coming down is easily equal to the power going up.

I was thinking that it would be more energy-efficient to shut off the motors at the highest point, and letting the quad free-fall and then turning the motors on again at 30 meters or so to right itself and slow down for landing.  Has anyone tried this?  I have been told that dji can do this.

I'm using APM and PixHawk controllers.

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  • Now THIS is intentionally shutting off motors and recovering at the last second :)


    No proper footage of yesterdays landing yet from geostationary launch, would love to see an onboard view from start to finish!

  • Did you see this video?


    "Interlock" might be just the feature you are looking for...  unless it too disarms the multirotor like emergency stop.

    • I didn't see it,and thanks for the link.  As I mentioned, I have modified several of the libraries in APM, so I could modify what the firmware does if I needed to. I try to modify the code as little as possible to avoid unintended consequences, but now and then, I come up with what I think is an improvement. I'm a bit reluctant to send the mods to GitHub, because I don't want anyone else to say that a mod that I made caused a problem for them.

      I have been playing with what happens when the motors are spinning in reverse. I have a test setup that runs a motor/prop combination a few inches from my 'test unit'  I spin that up which puts a lot of air by the UUT and spins that one backwards.  I then apply power to the UUT and see what happens.  So far, I have only tried one (cheap no-name) ESC,and the results weren't good (luckily, I have a 20A fuse in the power lead). I'll try a couple others and see what happens.

    • I am flying a 3DR Y6 and do it often while in Stabi-mode: Completely cut the throttle and let it free-fall and recover nicely. It might be the solution: once your auto-mission is complete, you return to Stabi, cut the throttle and let it fall to say 50 Meter and catch it. Mind you though that the copter might disarm if in idle for too long !

  • You could use a helicopter instead of a multirotor, and then just auto-rotate on the way down.  Controlled descent rate, full attitude control, zero power consumed.

  • I've done this with my Blade 350 QX. But not at the altitude you're talking about. I was maybe 250 feet up, cut throttle, and try to wait until the last moment to fire them up and recover. The 350 QX had some decent punch out and would only take about 15, maybe 10 feet from free fall speed to achieve hover and hold altitude again. 

    With the QX, bringing the throttle all the way down didn't fully stop the props. They would maintain idle, but it would still go completely silent and  drop extremely fast. I think maintaining at least some throttle would be wise. It will use a little bit more power, but it will also help maintain orientation, prop direction. That means less power will be spent flipping it back over or getting the props back up to speed. Plus the quad will still technically be in your control. Tumbling thousands of feet while flying blind (you said you couldn't see it when it went up that high), and expecting to eventually make visual contact with it and then step in and have all systems respond is dangerous and careless. If you quad is in the air, you should be piloting it. Even if it's a "controlled free fall", but tumbling blind is not piloting. Go 5 or 10% throttle at least. 

    I'll admit there was something cool about the sound of angry bees suddenly disappearing  and then swarming back in at the last minute to save the quad. But I never felt like it wasn't in my control. 

  • In a remote part of a country outside the US, away from commercial and GA air routes, I have taken a Phantom 2 with gimbal and GoPro up over a mile AGL on numerous occasions, for AP reasons.  I descend in what DJI calls manual mode, which is essentially idling the motors, unless I apply forward left stick.  I will let it free fall up to 10 m/sec descent rate, and the quad holds attitude well.  Sometimes I will give just a bit of throttle to drop descent rate to 6 m/sec.  I usually start spooling up around 200 meters, but will stay in manual mode until somewhere below 100 meters.  I trigger manual mode with the momentary switch SH on my Futaba 14SG radio, so if I experience brain lock, it's likely to come out of manual mode.  Regarding VRS, I've wondered how much dirty air is actually beneath my blades when idling down.  In any case, I'm ready with right stick forward if I sense VRS.  Throughout the descent, I am in the googles watching altitude, vertical speed and pack voltage.  Could one get down faster and on fewer mAH with motors off?  Sure.  Or in a dive?  Sure.  But idling down, or throttle just above an idle, avoids any motor/ESC risks, restart risks, major tumbling, etc.  Tumbling not great with 3 axis gimbal powered, and camera on board.  I also chose my descent location to be over soft vegetation, just in case. 

    • I'll have to try it sometime.  I have never flown a 'factory built' craft, so I can't accurately predict how any of my quads/hexes will perform (I have 8-10 of them), but I'll try some day soon.

      • Didn't you say it was a one time event, never to be repeated?

        • I was thinking of going over to Nevada and getting FAA approval to try for an altitude record.  I wanted to use virtually 100% of my batteries to go up.  Although I could use a parachute, that would be extra weight.

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Aug 25