Low battery RTH

WebMaximus · May 5, 2018

One thing I don't fully understand is the relation of the low battery warning setting in the app which is default set to 30% and the low battery RTH which in the manual is described as:

"The thresholds for the battery level warnings are automatically determined based on the aircraft's current altitude and distance from the Home Point"

What I don't understand is how this works when you're able to manually set the value for the low battery warning. What's the purpose having this setting in the app that you can adjust yourself when it's automatically calculated (which to me seems like a very good thing) when the aircraft needs to RTH to land safely?

MavicCF · May 5, 2018

WebMaximus said:
One thing I don't fully understand is the relation of the low battery warning setting in the app which is default set to 30% and the low battery RTH which in the manual is described as:

"The thresholds for the battery level warnings are automatically determined based on the aircraft's current altitude and distance from the Home Point"

What I don't understand is how this works when you're able to manually set the value for the low battery warning. What's the purpose having this setting in the app that you can adjust yourself when it's automatically calculated (which to me seems like a very good thing) when the aircraft needs to RTH to land safely?

There are several reasons, but here are two. Say you are filming a relatively close object and want to get as much footage as you can out of each battery. You are flying close-by so the battery level doesn't really concern you. Well at 30% a loud, constant beep starts and you can't turn it off. You planned to land at around 15-20% so you get to enjoy the nerve fraying alarm for several more minutes.
Another reason is if you are going on a long distance flight, coming back you are scraping it a little thin, maybe landing at around 15%, again you would need to listen to the provoking alarm for several minutes. Which is not fun, especially in a stressful situation like this would be.
Also, (Ok, this may be a third reason

) the auto RTH calculations aren't all that accurate, I have turned around on several long flights after being prompted by this warning and got back with 45-50% still remaining.
Anyway, a little long winded, but that's how I see it. -CF

WebMaximus · May 5, 2018

Thanks for the input and what you say makes sense but what I still fail to understand is if the setting in the app will affect the logic described in the manual?

In essence, is it the value you set for low battery warning that will trigger the aircraft to RTH or rather the calculation how much battery will be required based on how far away the aircraft is from its home point?

MavicCF · May 5, 2018

WebMaximus said:
Thanks for the input and what you say makes sense but what I still fail to understand is if the setting in the app will affect the logic described in the manual?

In essence, is it the value you set for low battery warning that will trigger the aircraft to RTH or rather the calculation how much battery will be required based on how far away the aircraft is from its home point?

They are two different things, the one that you set merely gives you an audible warning/alarm once it reaches that particular battery level. The automatic one is calculating wind, distance, altitude, etc and trying to decide how much time it will take to get home. Once it reaches the point where it thinks you will only be able to make it home on the remaining battery, it will automatically RTH unless you cancel it.

WebMaximus · May 5, 2018

Ok, that's good to hear that the logic isn't affected by the value you set in the app.

Will try all this out IRL as soon as I get a chance to.

Thanks again for your help how this works.

MavicCF · May 5, 2018

Just to illustrate this, here is a graph. In this, someone just went straight up and came straight down. You can see the Smart Battery Useful Time (the red line measured in seconds) drops to around 420 seconds of remaining flight time (based on the pitch, roll, throttle, etc up to that point). It decides that this is about how long it will take to get down to ground level, (still based on the same calculations) so it begins to Autoland. Now as it begins to descend, everything changes. Instead of struggling up, it can essentially just coast down using very little battery, thus making all the prior calculations incorrect.