Critical Low Power. Aircraft Landing.

[Balko]

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[Peter.smith]

To me it does seem the battery might have issues, I have read that DJI recommends to drain a battery down to its internal cutoff voltage (although they don't say how), and then fully recharge it, periodically (I don't recall when), to rejuvenate it. Also, I've read that a new battery needs several charge/drain cycles to become fully functional.

Or maybe the issue was some sort of overheat?

I am an electrical engineer with a long background in batteries. Rechargeable batteries of all types can develop a memory which relegates them to the top 70% if only discharged to 30% all the time. The first three cycles of any battery should be down to zero and up to 100% each time to set the memory there. I believe you can do this by setting battery warning low and then doing the last 10% on the ground by just running the motors. Reading individual cell voltages is worthless unless you plan to disassemble the pack and replace one cell which is generally not worth your time. Completely discharge the battery about every 10 cycles and you will get the best life and performance from your batteries.

 

[HFMan]

OMG... More old school 'advice'. LiPo batteries do not develop any kind of memory conditions. That's for ancient NiCd and to some degree NiMh.

 

[Pathogen]

Interpretting the manual,

OMG... More old school 'advice'. LiPo batteries do not develop any kind of memory conditions. That's for ancient NiCd and to some degree NiMh.

Not that it matters much anymore since cadmium has or is being banned everywhere, one can potentially (no pun intended) avoid NiCd memory effect by avoiding draining them down to the exact same voltage each cycle. Also, despite popular opinion,, fully emptying a NiCd is a fantastic way to prematurely age it.

 

[robee683]

Wow, didn't appreciate that my incident would promote such an extensive response especially with regard to battery drain when flying into the wind.

The attention to this aspect appears to arisen from CyberNate's analysis of my flight log where it says that " According to the flight log, you were flying into the wind in sport mode. This is apparent as you were seeing speeds around 36. You probably had around a 10 mph headwind."

In my original post I stated that I flew in "ideal conditions with no wind and about 15C". And yes, I was flying in a Sport Mode.

Here is an image of my weather station for the day of my flight ie June 16 and it shows that the maximum wind speed for that day (upper left) was 8kph (5mph). For those not familiar with this weather station in the lower right it shows the minimum and maximum high speeds for the last 25 days.

Unfortunately I can't provide the wind speed at the precise time of the flight but I suggest it was negligible and would have had little effect on the forward flight.

So I am interested in knowing what CyberNate saw in the Flight Log that lead to the conclusion that I was flying into a headwind and hence the significant discussion.

IMHO I think the problem was probably a low level battery, cool conditions, and high drain flying not long after takeoff.

 

[Cymruflyer]

Ahhh, understand now HFMan. So it uses the GPS ground speed to adjust throttle, slowing down in a down wind situation and increasing speed, to what ever its maximum is when flying into a headwind. Apologies.

 

[dannyw777]

Agree great info thanks gentlemen

 

[CyberNate]

Wow, didn't appreciate that my incident would promote such an extensive response especially with regard to battery drain when flying into the wind.

The attention to this aspect appears to arisen from CyberNate's analysis of my flight log where it says that " According to the flight log, you were flying into the wind in sport mode. This is apparent as you were seeing speeds around 36. You probably had around a 10 mph headwind."

In my original post I stated that I flew in "ideal conditions with no wind and about 15C". And yes, I was flying in a Sport Mode.

Here is an image of my weather station for the day of my flight ie June 16 and it shows that the maximum wind speed for that day (upper left) was 8kph (5mph). For those not familiar with this weather station in the lower right it shows the minimum and maximum high speeds for the last 25 days.

Unfortunately I can't provide the wind speed at the precise time of the flight but I suggest it was negligible and would have had little effect on the forward flight.

So I am interested in knowing what CyberNate saw in the Flight Log that lead to the conclusion that I was flying into a headwind and hence the significant discussion.

IMHO I think the problem was probably a low level battery, cool conditions, and high drain flying not long after takeoff.

No, I over estimated the wind speed for sure. After mentioning that I flew in some wind to see the affect on top speed. It was more 4 to 5 mph, but the point is that the motors were pushed more going out. Top speed is normally 40, GPS ground speed limited and probably 42-43mph air speed limited at full right stick. But even with less wind, you are stressing the motors in sport mode which will push the motor to maximum RPM and current draw as it attempts to reach up to 40mph ground speed with maximum pitch.

Wind is also higher at elevation and at different points on the terrain, such as valleys and over the tops of hills

 

[Jenkins]

After I fly I come home and charge batteries that I've used ready for next time. Is this wrong then? If it is it really should be clearly outlined by DJI as I would imagine charging a battery after you use it is pretty common.

 

[msinger]

After I fly I come home and charge batteries that I've used ready for next time. Is this wrong then?

It's not wrong, but it's not necessary if your batteries are above 30% and you're not going to fly again before they start auto discharging.

For example, if you're planning on flying tomorrow and the "Time to Discharge" setting is set to 2 days, then it would be fine to charge them again right away. However, if you're not planning on flying again for 7 days, then it would not make sense to charge them since they will start to auto discharge 2 days after you recharge them.

 

[Balko]

It's not wrong, but it's not necessary if your batteries are above 30% and you're not going to fly again before they start auto discharging.

For example, if you're planning on flying tomorrow and the "Time to Discharge" setting is set to 2 days, then it would be fine to charge them again right away. However, if you're not planning on flying again for 7 days, then it would not make sense to charge them since they will start to auto discharge 2 days after you recharge them.

View attachment 15738

So if we haven't used the fully charged battery for a couple of days, how is the proper way to charge it if there's still 97% power in it?

 

[msinger]

So if we haven't used the fully charged battery for a couple of days, how is the proper way to charge it if there's still 97% power in it?

Put it back on the charger and wait for it to recharge.

 

[Ian in London]

This statement is totally wrong, but understandable coming from anyone who is not a real sUAV pilot, due to their misunderstanding of modern sUAV flight control systems and how they manage ground speed vs. airspeed.

As a real pilot with a ticket, I know how to do real flying just like maybe you. I also understand the details of the rather sophisticated flight control system for the Mavic, 'cause I'm a real sUAV pilot!

Nate is right, and you are wrong. The reason is, you don't understand that the Mavic has ground speed information available via GPS, and the on-board controller tries to maintain a ground speed relative to stick input. So, when flying into the wind, the aircraft will fly at a faster airspeed (that's one of those fancy terms real pilots that do real flying know about) than with a tailwind.

Real aircraft generally don't have systems like this because that would be far too much interference in control for real flying, and real pilots wouldn't put up with it.

Sorry. Are you a real pilot or just a real sUAV pilot, and do you fly real aircraft, or just real UAVs, and is that with real airspeed sensors and indicators or just real GPS-based ground speed indicators. Or, more fundamentally, are you just real bad at expressing yourself in a constructive, helpful way to anyone you believe to be less experienced or knowledgeable than yourself?

On a serious note, it's a little arrogant to say that someone who has only flown modern GPS-based UAVs is less of a pilot to their craft than someone like yourself you has obviously learned to fly pre-GPS based craft. You learn your skills relative to the craft you're flying. And from my experience, the Mavic flies much slower into a head wind than it does along a tail wind and I think that's something that every real Mavic pilot knows. Remember this hobby is about having fun, and these forums are about helping people in a constructive and intelligent manner... Try not to take yourself too seriously

 

[CyberNate]

Sorry. Are you a real pilot or just a real sUAV pilot, and do you fly real aircraft, or just real UAVs, and is that with real airspeed sensors and indicators or just real GPS-based ground speed indicators. Or, more fundamentally, are youjust real bad at expressing yourself in a constructive, helpful way to anyone you believe to be less experienced or knowledgeable than yourself?

On a serious note, it's a little arrogant to say that someone who has only flown modern GPS-based UAVs is less of a pilot to their craft than someone like yourself you has obviously learned to fly pre-GPS based craft. You learn your skills relative to the craft you're flying. And from my experience, the Mavic flies much slower into a head wind than it does along a tail wind and I think that's something that every real Mavic pilot knows. Remember this hobby is about having fun, and these forums are about helping people in a constructive and intelligent manner...

It's all good guys. Just what came to mind for me when I far the original post. We just do our best to interpret the data. No need for conflict. If there's something useful in my analysis, great. If not, disregard. I've been wrong plenty of times ;-).

 

[Balko]

Put it back on the charger and wait for it to recharge.

I thought that, like with the batteries of the Phantom 3, that we have to turn it ON first, unless it is below 95%, so that it'll start to charge.

 

[Balko]

Put it back on the charger and wait for it to recharge.

Oh, okay. What I did was, like with the battery of my P3A, I turned on the bat before attaching to the charger. No wonder it took a longer time for the Mavic bat to charge fully the remaining 3%...and the lights didn't go Off, it just stopped blinking.

Thank you for the advice, msinger.

 

[stratos]

To me it does seem the battery might have issues, I have read that DJI recommends to drain a battery down to its internal cutoff voltage (although they don't say how), and then fully recharge it, periodically (I don't recall when), to rejuvenate it. Also, I've read that a new battery needs several charge/drain cycles to become fully functional.

Or maybe the issue was some sort of overheat?

I havent done it yet with mines but I think it would be a good idea to refreshe them

 

[Peter.smith]

OMG... More old school 'advice'. LiPo batteries do not develop any kind of memory conditions. That's for ancient NiCd and to some degree NiMh.

Then why does DJI give this advice?