Inadvertent takeoff

[Arve Horgheim]

At 5 degrees C I flew the aircraft down to 18% battery capacity. The last 15% at low hover.

I landed, but my intention was to drain the battery down to 7 %. The wind was picking up a bit, so I brought the Phantom close to my house in shield by the entrance door, surrounded by obstacles. This was approximately 35 m from my home point where I landed. My next step and plan was to start it up and run on idle until I reached 7 %, propellers on.

Everything looked good for about 15 sec. Then the motors increased in RPM and the Phantom took off. I grabbed the controller and tried to get control, but did not. Control inputs did not give any results. I pressed the RTH-button and then l regained control. Height was about 16 m. Landed immediately (safe, 52 sec/14% left), knowing I was low on power. This sequence took about 15 sec.

After the incident, I think I realized what happened (replayed the flight). When the battery capacity hit the H-icon on the timeline, the Phantom decided to go home. 3 sec after start: Tips, RC assisted takeoff (visible for 5 sec). Then, after a total of 13 sec: Tips, low power, returning to the home point (35 m away). It took off. According to the manual, you do not have any control until it reaches 20m height.

1. I have learned a lesson, but have not seen any warning about this in the manual.
   
   
2. The software logic should prevent the Phantom to take off when low on power and idling on ground.
   

 

[joeb1999]

Tldr. Why would you ever discharge a lipo battery down to 7%? You need a balance charger to discharge an calibrate it. All your doing is damaging it running it that low. I never run mine below 20%. And never fly under a full zap.

 

[msinger]

have not seen any warning about this in the manual

 

[msinger]

Why would you ever discharge a lipo battery down to 7%? You need a balance charger to discharge an calibrate it.

You're supposed to cycle the battery every 20 charges. This is one of the ways DJI recommends discharging the battery. The OP should have stayed within 20 meters of the home point -- or reset the home point after he moved.

 

[Meta4]

Or taken the props off.
It's never a good idea to leave a Phantom idling with props on.
If you have to, strap the landing gear down.

 

[Arve Horgheim]

Agree. But just a reminder for all of us stupid. The text, page 21 in the last manual, tells that you can actually fly until its less than to 8% to drain the battery. Its easy for experinsed pilots to say what should be done. It should be written in the manual and made it impossible in the software

 

[msinger]

AThe text, page 21 in the last manual, tells that you can actually fly until its less than to 8% to drain the battery.

That is accurate. It's also best done when your Phantom is within 20 meters of the home point. Otherwise, it'll try to return to home when the battery is low.

 

[QuadBart]

I've run Lipo for years in R/C cars I raced. I know that doesn't make me an expert on the subject, doing some simple things have kept my batteries in good running order even when stored for a few (3) years...

I never store my batteries (extended periods) fully charged
I store my batteries in whatever "state" or level of charge remaining after a full flight (or run in the case of my RC cars).
I've not had any issues with batteries over the years doing it this way. No puffing/swelling no dead cells...

 

[msinger]

QuadBart, your advice pretty much mirrors what DJI recommends. As far as I know, cycling the battery every 20 charges does nothing other than rebalance the battery cells.