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[cderoche]

Its kind of fascinating how different capacity packs can burn down evenly. Can anyone explain how?

They probably equalize during the voltage reduction. In other words the big pack charges the smaller one.

 

[cderoche]

Crashed my new stock Mavic today REALLY hard on concrete trying to reach 30K out and back stock. Too much head wind coming back and came up 306ft short of making back after going 29,180ft out. Flight time of 23:00 going 31.6mph out and 26-27mph back into headwind. I charged this battery a couple days ago. Should have charged it this morning before flight. Probably would have made it. It's a cooler day than usual as well, so that's not helping. Was amazing that it was still flying at around 2.5V per cell. Was so close I had to go for it.

Now I have broken camera sensor, broken processor board (probably), battery casing trashed, and who knows what else. Won't even start. The DJI boot sound gets cut off and Mavic never finishes initialization. Flying over a parking lot is not a good idea when you're at 0 percent battery. Fortunately no cars hit. I'll get it fixed up. I'm pretty much a ninja with fixing stuff on the Mavic these days.

View attachment 23491

View attachment 23492

**** dude hope you get it fixed up, glad it only hit concrete.

 

[CyberNate]

hey cybernate, can you step us through what happens once you hit 3.4 volts down to 2.5 volts (or crash) and how you react? Got a lot of new folks and there are 200+ pages of articles to read to find this stuff.

At 3.4V the critical autolanding kicks in and it will start decending. I nudge the elevator stick up until I see altitude maintained and then I'll back off just bit to perhaps take a bit of altitude off if needed. You want to be very low at this point as the battery can drop off very fast below 3.4V. In my case I was very close to home and I decided to just go for it. I couldn't be as low as needed because there is a hill right before the spot I'm flying from as well as some trees. This was make or break time I simply couldn't make it. Once you hit 3.0V at speed, you have maybe 20 seconds before Mavic will drop out of the sky. You need to be low and going for landing at this point. I pushed ahead and failed. I really didn't have a good spot to land, though I suppose I could have tried for the parking lot I was flying over. I would have had to drop a lot of altitude quickly to do that. Checking my controller flight log I see that I flew on critically low battery (sub 3.4V) from over 2500ft out. That's really asking too much of the Mavic. I needed to be less than 2000ft out when autolanding kicked in, especially with the headwind I had.

*** keep in mind this is a stock mavic with platinum 8331 props. If you have a lot of weight, it may not be able to fly at such low voltage. With 8330 propellers, you also can't fly with voltage that low as they need more rpm for lift. I was flying at sub 2.5V per cell at the end and maintaining altitude briefly, but voltage fell off quick.

Here is link to the flight log:
DJI Flight Log Viewer - PhantomHelp.com

 

[beanbubba]

At 3.4V the critical autolanding kicks in and it will start decending. I nudge the elevator stick up until I see altitude maintained and then I'll back off just bit to perhaps take a bit of altitude off if needed. You want to be very low at this point as the battery can drop off very fast below 3.4V. In my case I was very close to home and I decided to just go for it. I couldn't be as low as needed because there is a hill right before the spot I'm flying from as well as some trees. This was make or break time I simply couldn't make it. Once you hit 3.0V at speed, you have maybe 20 seconds before Mavic will drop out of the sky. You need to be low and going for landing at this point. I pushed ahead and failed. I really didn't have a good spot to land, though I suppose I could have tried for the parking lot I was flying over. I would have had to drop a lot of altitude quickly to do that. Checking my controller flight log I see that I flew on critically low battery (sub 3.4V) from over 2500ft out. That's really asking too much of the Mavic. I needed to be less than 2000ft out when autolanding kicked in, especially with the headwind I had.

*** keep in mind this is a stock mavic with platinum 8331 props. If you have a lot of weight, it may not be able to fly at such low voltage. With 8330 propellers, you also can't fly with voltage that low as they need more rpm for lift. I was flying at sub 2.5V per cell at the end and maintaining altitude briefly, but voltage fell off quick.

Here is link to the flight log:
DJI Flight Log Viewer - PhantomHelp.com

Thx, great description. What was the condition of your battery for this flight? How many times charged and how many times had it seen sub 3.4 volts?

@SkyNinja, same questions to you on your last swimming lesson.

I am putting together a spreadsheet of these fringe events to try and publish some basic guidelines.

 

[SkyNinja]

You might want to backup a couple hundred yards off the shore until you figure this out

You're right, maybe a few hundred yards

Crashed my new stock Mavic today REALLY hard on concrete trying to reach 30K out and back stock. Too much head wind coming back and came up 306ft short of making back after going 29,180ft out. Flight time of 23:00 going 31.6mph out and 26-27mph back into headwind. I charged this battery a couple days ago. Should have charged it this morning before flight. Probably would have made it. It's a cooler day than usual as well, so that's not helping. Was amazing that it was still flying at around 2.5V per cell. Was so close I had to go for it.

Now I have broken camera sensor, broken processor board (probably), battery casing trashed, and who knows what else. Won't even start. The DJI boot sound gets cut off and Mavic never finishes initialization. Flying over a parking lot is not a good idea when you're at 0 percent battery. Fortunately no cars hit. I'll get it fixed up. I'm pretty much a ninja with fixing stuff on the Mavic these days.

View attachment 23491

View attachment 23492

Sorry to hear that you didn't make it. At least you ended up a little better than i did with a bird you can repair or use for parts. Concrete is better than deep dark water.

 

[CyberNate]

Thx, great description. What was the condition of your battery for this flight? How many times charged and how many times had it seen sub 3.4 volts?

@SkyNinja, same questions to you on your last swimming lesson.

I am putting together a spreadsheet of these fringe events to try and publish some basic guidelines.

Actually this was a well used battery. It's the one I did my 54k flight back in late May. It's probably had 40 or more deep cycles (need to verify). It works better than a new battery I bought a few weeks ago.

 

[SkyNinja]

Thx, great description. What was the condition of your battery for this flight? How many times charged and how many times had it seen sub 3.4 volts?

@SkyNinja, same questions to you on your last swimming lesson.

I am putting together a spreadsheet of these fringe events to try and publish some basic guidelines.

Stock DJI battery had 2 flights on it never flown below 30%. Purchased this battery a couple weeks ago for the long range flight.
1# Protek 3600 4 flights on the battery one of the 4 Flights the battery was run down to 1%.
2#Protek 3600 had 0 flights on it. It was a replacement battery after a propeller strike killing a cell on its predecessor.

 

[beanbubba]

Here is a chart of the last 3 reported crashes. This illustrates cybernate's comments about how the percentage display is highly variable. Anyway, these 3 flights appear to be on the fringes of this debate and this chart is probably a good guidepost to follow.

View attachment 23511

 

[CyberNate]

View attachment 23512 Here is a chart of the last 3 reported crashes. This illustrates cybernate's comments about how the percentage display is highly variable. Anyway, these 3 flights appear to be on the fringes of this debate and this chart is probably a good guidepost to follow.

View attachment 23511

Your graph illustrates that I should have charged it the day of the flight rather than 2 days before. Started at lower voltage. Thanks for compiling the data.

 

[lolo780]

The rear hinge detents are quite heavy, and once the joint is locked with a screw, you can ditch the rear plastic tab that always bends anyways. More weight gone plus better aero for the rear props.

I also scraped off 0.3g of excess thermal compound. DJI is very generous with that stuff. Same with the black goo they secure wires with. Over 1g savings by applying sparingly.

I'm looking at a solution for the front arms right now to see if it's worthwhile. Up front it's a bit more complicated and maybe not as heavy.

 

[beanbubba]

The rear hinge detents are quite heavy, and once the joint is locked with a screw, you can ditch the rear plastic tab that always bends anyways. More weight gone plus better aero for the rear props.

I also scraped off 0.3g of excess thermal compound. DJI is very generous with that stuff. Same with the black goo they secure wires with. Over 1g savings by applying sparingly.

I'm looking at a solution for the front arms right now to see if it's worthwhile. Up front it's a bit more complicated and maybe not as heavy.

I actually saved these in a zip lock bag after removal from this past summer. Might as well pile on some more shed weight!

 

[lolo780]

Is the magnesium plate just for WiFi interference with the GPS?

 

[beanbubba]

View attachment 23512 Here is a chart of the last 3 reported crashes. This illustrates cybernate's comments about how the percentage display is highly variable. Anyway, these 3 flights appear to be on the fringes of this debate and this chart is probably a good guidepost to follow.

View attachment 23511

The previous chart did not highlight the last 2 minutes of flight that is very interesting. Check this out, skyninja had the only non damaged battery here with "normal" behavior. Cybernate shows a voltage increase at the end?? And beanbubba shows flight conclusion at 4.6% battery and 3.4 volts?? All I can surmise from this data is that damaged batteries are very unpredictable.

 

[lolo780]

Don't forget battery mod vs stock. Would be useful to see current draw and battery temp.

 

[CyberNate]

The previous chart did not highlight the last 2 minutes of flight that is very interesting. Check this out, skyninja had the only non damaged battery here with "normal" behavior. Cybernate shows a voltage increase at the end?? And beanbubba shows flight conclusion at 4.6% battery and 3.4 volts?? All I can surmise from this data is that damaged batteries are very unpredictable.

View attachment 23516

The voltage increase on mine is due to the motors shutting off. When you stop current draw the voltage will come back to some degree. I was close enough that I maintained connection.

 

[cderoche]

@JakeMaxxUAV

Stock antenna, battery mod, edged out my old distance with 33,133ft (6.2miles) out today with a brand new 5200mah Multistar LiHV pack on top. Way too much wind (~15mph) to do any better. Got out very far very fast with lots of battery left, and I needed every bit of it on the windy way back. Next time I'll fly more to the right to straighten it up, & on a less windy day... I didn't want to fly over the Mississippi River that far out and encounter a problem.

 

[beanbubba]

The voltage increase on mine is due to the motors shutting off. When you stop current draw the voltage will come back to some degree. I was close enough that I maintained connection.

Anyone have a theory why mine dropped from the sky for no reason and had 3.4v still in the tank?

 

[CyberNate]

Anyone have a theory why mine dropped from the sky for no reason and had 3.4v still in the tank?

Too heavy perhaps.

 

[lolo780]

Anyone have a theory why mine dropped from the sky for no reason and had 3.4v still in the tank?

What's your total weight and avg wattage?

 

[lolo780]

11.3 more grams off. With the vented upper bodywork I'm actually running too cold and ended up taping over some holes. Definitely no need for a fan so on the shelf it goes.

Disclaimer: The core board will shut down if it over temps. Test thoroughly before any long range flights.