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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Who told you that...

A friend who says he has a friend....

I know that it might not be true.  Nonetheless,I was wondering if anyone has tried it with an APM.

I have a small quad with a KK2 controller.  I pushed the throttle all the way up and it climbed so fast it scared me (I was new to the sport at the time), so at approximately 200' in altitude, I pulled the throttle all the way down. Inertia kept it going up for a short time, then it started falling - motors off.  It did not stay upright, it was tumbling. It took me a short time to regain my composure and push the throttle up again. At a height of about 50', the little quad caught itself and kept on flying. I did NOT have the "motors spin when armed option ON", so they actually stopped.

So a KK2 can do it.  

I am reluctant to try the same thing with any of my newer, bigger aircraft.  The cost of failure is too high.

There is a new APM flight mode called "Throw Mode" being developed. When/if released, it may do what you need, but I'm not sure. You can see a video demonstrating it here.

Keep it under control - I have come up with a new checklist that covers all the new FAA regs.  Please consider it on UASchecklist.com.  It will keep all UAV/Drone users out of trouble.

As I mentioned, I was outside the US (on a British Caribbean Island).  Maybe the same rules apply there, but when I asked a local policeman, he said he knew of no limitations, so I did what I always wanted to do in the US, but could not do because of regulations.

Hi Charles,

I'm pretty sure the recovery would work fine right now in several of the flight modes.

The only thing missing is a means to tell it when to turn off the motors and then when to re-enable them.

In theory I believe you are correct, would use less power, because you would only have to counter descent from free fall speed.

I believe 30 meters might be about the minimum you would want to reengage though, still has to go through some gymnastics  before it can add thrust.

Seems like you could still test this in the US just fine, just stay below 400 feet when you turn off the motors.

Now all you need is somebody to put together the crash dive mode.

This looks like it would probably do what I want.  Is there any code on GitHub? I looked around and didn't see any.

Cool video - Thanks!

I just might be able to do this myself.  I normally write firmware for Microchip PICs,  but I have already modified APM firmware in several areas (and it seems to work!)

Turning the motors during flight is dangerous, it's really possible, that they won't spin up again.

Isn't it a better way to somehow increase the descend speed?

Hi, yes it works suprisingly well, I've tried it several times while getting familiar with 'edge of the envelope' scenarios.  It will of course tumble on the way down but when you apply throttle it should right itself even when inverted.  I would certainly restart before 30 meters though!  More like a 100 meters at least, preferably higher, as it will essentially be falling at terminal velocity from that height.  Also I haven't tried it since DCM (3.2 firmware) days, it may be that if you're tumbling that high and that long that the EKF in the recent firmware (3.3/3.4) takes a little longer to recover or may get very upset and throw a hissy fit.

Coming down in a straight line is very slow because you're descending through prop wash and it's very aerodynamically unstable.  You can descend very quickly if you add an angle to the descent so it no longer comes down through it's own wash.  You could try and zig-zag downards like a skier down a mountain, it would get you down much faster, or in a spiral.  There's no flight mode that will do that, but you could use guided mode and code something or possibly even use auto mode and code a mission to do similar.

Very interesting task, please let us know how you get on :)

It's happen to me by accident that motors stop in the air and switching to stab I can recover and land safety but that don't warantee that a prop become spin reverse and you burn an esc and crash, take in mind that occurs too and is a risk; I prefer other suggestinos descending as slaloon or perhaps a parachute? but try to not complete stop motors. 

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