You CAN switch off the motors to save battery during a descent.
You CAN relight the engines and regain stability of the drone during freefall, even if the drone is upside down.
It makes a lot of sense to do so given that the Mavic's descent rate is rather slow and you can waste valuable battery time getting the drone down. In the DJI app settings, the setting for switching off the motors should be set to "CSC Maneuver" as opposed to the default setting of "Emergency Only".
Once in freefall, the Mavic may spin and even fall upside down (example in my video), but from experience (and I've done this a couple of times), the engine relight will stabilize the drone really really fast. As a matter of fact, in my video, you can see the drone freefalling, and even it doesn't seem like it's falling too fast, with the naked eye it is much more dramatic, and by the time I've done the relight I was still quite high and could have pushed it further.
There's no flight data. The Mavic stops the current flight and once the relight happens, a new one gets started. The battery used during a +200m descent was <1% ∴ massive savings.
Obviously, this shouldn't be done above people or property. You should ensure that you won't have any obstacles that may impair the signal during the maneuver.
Another thing to point out is to keep an eye out for the Mavic in the initial phase of the freefall, but once you've committed to relighting the engines you should definitely be looking at the controls and check for RPM coming alive, once that happens you know the relight was activated because there is a little lag of 1s or so when you give the command to start/stop the engines.
Even though this works, personally, whenever I do it, I always assume 2 things may happen:
- The relight may fail and the drone is gone.
- The gimbal may not handle the spins and break.
So far, none of those have happened, but if it ever does I won't be that surprised.
Another thing I'm absolutely sure that can be of value to the Mavic in order to not only save battery time but extend it, is to build a malleable case that can be filled up with Helium in order to decrease the Mavic's weight. I've been working on a concept in my free time albeit it is not at the top of my priorities at the moment.
