Battery Level Indicator Bar

[Srcrain]

I was out flying yesterday and noticed that the "H" (return to home level) on the battery level indicator bar doesn't seem to be very accurate. I thought it was supposed to indicate the point which the battery is only enough to RTH. I also have 20% and 10% battery warnings levels set.

The specific example was that I was literally about 5 feet from my home point but the "H" on the indicator bar was above 20% my first warning level. This was a dangerous since it initiated a RTH, but since it was within a few feet decided to land immediately (DJI failsafe I guess). I launched at the edge of a pier so it was hovering over water when it started its decent. I was hovering low (a few feet) to wait for some pedestrians to walk by before landing on the pier.

Has anyone else experienced an issue with the RTH and "H" triggering way before it needs to?

 

[old man mavic]

I was out flying yesterday and noticed that the "H" (return to home level) on the battery level indicator bar doesn't seem to be very accurate. I thought it was supposed to indicate the point which the battery is only enough to RTH. I also have 20% and 10% battery warnings levels set.

The specific example was that I was literally about 5 feet from my home point but the "H" on the indicator bar was above 20% my first warning level. This was a dangerous since it initiated a RTH, but since it was within a few feet decided to land immediately (DJI failsafe I guess). I launched at the edge of a pier so it was hovering over water when it started its decent. I was hovering low (a few feet) to wait for some pedestrians to walk by before landing on the pier.

Has anyone else experienced an issue with the RTH and "H" triggering way before it needs to?

there is a lesson to be learned there @Srcrain the battery levels are really to low i have mine at 40% first warning and 25% critical that way you get more time to land as you said you were waiting for a clear space to land, the problem is the battery voltage drops off very quickly at low levels,and as you found out, that can catch you out

 

[Srcrain]

That is good advice, thanks. I do normally land well before warnings, typically 25%. I am just trying to not be annoying to the people around me with the battery warning beep.

Still wondering about the "H" on the indicator bar. Is it because of quick voltage drop at low battery levels?

 

[tcope]

I was out flying yesterday and noticed that the "H" (return to home level) on the battery level indicator bar doesn't seem to be very accurate. I thought it was supposed to indicate the point which the battery is only enough to RTH. I also have 20% and 10% battery warnings levels set.

The specific example was that I was literally about 5 feet from my home point but the "H" on the indicator bar was above 20% my first warning level. This was a dangerous since it initiated a RTH, but since it was within a few feet decided to land immediately (DJI failsafe I guess). I launched at the edge of a pier so it was hovering over water when it started its decent. I was hovering low (a few feet) to wait for some pedestrians to walk by before landing on the pier.

Has anyone else experienced an issue with the RTH and "H" triggering way before it needs to?

I'll see if I can break down few things but just going by memory....

RTH won't initiat within 30' of the home point (I know this is Smart RTH but I think it might be RTH as well). If the RTH indicator was at 20%, the battery level should have been at that or higher. So I'm not sure why RTH would have been initiated. If you have a warning at 20% and critical (I think it is listed as that) at 10% then when the lowest cell gets to 10%, the Mavic is going to land where it is. Perhaps if RTH was at 20% and the over all power left was at that, the lowest cell could have dropped to 10%. As mentioned, this is why you want to be around your home point at 30% battery (not RTH level) and pretty much landing at that point.

I'd recommend that you change your settings to show the lowest battery voltage and monitor that amount. Don't go by the RTH amount and rather look at the battery percent on the other side of the screen.

 

[brett8883]

I was out flying yesterday and noticed that the "H" (return to home level) on the battery level indicator bar doesn't seem to be very accurate. I thought it was supposed to indicate the point which the battery is only enough to RTH. I also have 20% and 10% battery warnings levels set.

The specific example was that I was literally about 5 feet from my home point but the "H" on the indicator bar was above 20% my first warning level. This was a dangerous since it initiated a RTH, but since it was within a few feet decided to land immediately (DJI failsafe I guess). I launched at the edge of a pier so it was hovering over water when it started its decent. I was hovering low (a few feet) to wait for some pedestrians to walk by before landing on the pier.

Has anyone else experienced an issue with the RTH and "H" triggering way before it needs to?

So with the smart battery function enabled it will RTH when it thinks it only has enough power to get home and land on the ground with 20% battery remaining. This can be ignored by pressing the RTH button. It can also be set higher than 20% but not lower.

When the aircraft thinks it only has enough power to land and still have 10% battery remaining after landing it will initiate auto-landing. You can’t ignore this but you can full throttle up and it will climb slowly. This can also be programmed higher than 10% remaining on landing but not lower.

The last failsafe occurs when any battery cell reaches 3.4 volts the drone will auto land and can’t be stopped. You can slow it’s decent and continue to fly forward and back but not stop it coming down entirely. Since this is based of cell voltage there’s no guarantee there’s actually enough battery to land safely left but it’s a last ditch effort. Hopefully you won’t get to this point.

Turning the warning level for the smart battery down to 20% essentially turns it off since that’s the level at which it will RTH. The calculation of how long it would take to RTH likely doesn’t factor in the close to home RTH procedure (speculation) in your case it was close enough that it just landed but the RTH calculation was probably factoring in the ascent to your specified RTH altitude and then landing from that altitude(again speculation) once the low battery RTH is triggered it then initiated the RTH procedure which dictated that it was close enough to home to just land.

This is my understanding of how the low-battery RTH works based on my exploration of the firmware. Could have something slightly off but I think I’m real close.

 

[Srcrain]

So with the smart battery function enabled it will RTH when it thinks it only has enough power to get home and land on the ground with 20% battery remaining. This can be ignored by pressing the RTH button. It can also be set higher than 20% but not lower.

When the aircraft thinks it only has enough power to land and still have 10% battery remaining after landing it will initiate auto-landing. You can’t ignore this but you can full throttle up and it will climb slowly. This can also be programmed higher than 10% remaining on landing but not lower.

The last failsafe occurs when any battery cell reaches 3.4 volts the drone will auto land and can’t be stopped. You can slow it’s decent and continue to fly forward and back but not stop it coming down entirely. Since this is based of cell voltage there’s no guarantee there’s actually enough battery to land safely left but it’s a last ditch effort. Hopefully you won’t get to this point.

Turning the warning level for the smart battery down to 20% essentially turns it off since that’s the level at which it will RTH. The calculation of how long it would take to RTH likely doesn’t factor in the close to home RTH procedure (speculation) in your case it was close enough that it just landed but the RTH calculation was probably factoring in the ascent to your specified RTH altitude and then landing from that altitude(again speculation) once the low battery RTH is triggered it then initiated the RTH procedure which dictated that it was close enough to home to just land.

This is my understanding of how the low-battery RTH works based on my exploration of the firmware. Could have something slightly off but I think I’m real close.

Thanks. This answers my question perfectly! I didn't realize that it initiated smart RTH at 20%. My battery was at around 22% so it was probably calculating raising altitude (350ft) before landing. Going up and down over 300 feet would definitely use 2% battery life. And as you said, since I was within a few feet (2m I think) of the home point it started landing at that spot. I was aware enough to move it to dry land before it dunked in the water but it was scary. Since it was only a few feet above the water I had very little time to react.

So the "H" on the indicator bar will never be below the 20% level.

 

[brett8883]

Thanks. This answers my question perfectly! I didn't realize that it initiated smart RTH at 20%. My battery was at around 22% so it was probably calculating raising altitude (350ft) before landing. Going up and down over 300 feet would definitely use 2% battery life. And as you said, since I was within a few feet (2m I think) of the home point it started landing at that spot. I was aware enough to move it to dry land before it dunked in the water but it was scary. Since it was only a few feet above the water I had very little time to react.

So the "H" on the indicator bar will never be below the 20% level.

That’s indicating how much flight time the drone THINKS is needed to return to the homepoint and land with 20% battery remaining. You notice when you fly away from the home point that indicator will move to the right indicating more time is required to make it back.

So you can see the importance of only taking off with a full battery. The algorithm that controls this must know the full charge capacity of the cells to accurately determine flight time.

 

[brett8883]

Also why having some amount of low battery warning above 20% is critical. Even if it was at 22% or something you would have known, “ok this thing is about to RTH and I close enough for a “close to home (Auto-landing)” RTH or will it rise up to my RTH height? It at least gives you a little heads up that you should think about before it just does it without warning.

 

[Srcrain]

Also why having some amount of low battery warning above 20% is critical. Even if it was at 22% or something you would have known, “ok this thing is about to RTH and I close enough for a “close to home (Auto-landing)” RTH or will it rise up to my RTH height? It at least gives you a little heads up that you should think about before it just does it without warning.

Great advice. Thank you. I am going to make that change tonight.

Also, another somewhat related topic that I just read in the manual for people interested and following this topic

"If the aircraft is between 5m and 20m from the home point when the RTH procedure begins:
i. If the RTH at Current Altitude option is enabled the aircraft flies to the home point at the current altitude, unless the current altitude is less than 2m, in which case the aircraft ascends to 2m and then flies to the home point.
ii. If the RTH at current altitude option is disabled, the aircraft lands immediately."

I think I may have also had this option disabled thinking it would rise to the standard RTH altitude. I didn't realize it would land immediately.

 

[DanMan32]

I do not believe there is any setting that can change when low battery RTH is triggered. It is dynamic, taking many things into account. Also when close to home point, "smart" RTH tends to be conservative.

As for critically low battery, you can keep flying for quite a while, though you have to up-throttle to counter the decent. This has been proven by many who have gotten caught at long distances and flown sub-zero SoC. Billy Kyle did that once.
I'll admit though, not sure what voltage will have the quad give up, and if that would be a sudden shutdown, or an attempt at a graceful landing.

 

[brett8883]

I do not believe there is any setting that can change when low battery RTH is triggered. It is dynamic, taking many things into account. Also when close to home point, "smart" RTH tends to be conservative.

As for critically low battery, you can keep flying for quite a while, though you have to up-throttle to counter the decent. This has been proven by many who have gotten caught at long distances and flown sub-zero SoC. Billy Kyle did that once.
I'll admit though, not sure what voltage will have the quad give up, and if that would be a sudden shutdown, or an attempt at a graceful landing.

It’s about 3.2-3.3 volts per cell it will turn off but that could be seconds after the failsafe forced landing starts at 3.4volts just due to the way lithium ion works

 

[wmjray]

That’s indicating how much flight time the drone THINKS is needed to return to the homepoint and land with 20% battery remaining. You notice when you fly away from the home point that indicator will move to the right indicating more time is required to make it back.

So you can see the importance of only taking off with a full battery. The algorithm that controls this must know the full charge capacity of the cells to accurately determine flight time.

Here’s an in-depth video overview of the battery bar.