It appears hitting the battery failsafe will initiate LAND rather than RTL. Is there any way to make it RTL instead? I realize landing is better than falling out of the sky. But not if it landing on Grumpy Aunt Bertha out for her morning walk. I set my battery threshold essentially as bingo fuel. Always enough left to come back for a normal landing based on where I'm flying. If I'm not paying attention failsafe initiates, I don't want it to land itself in my lake. I want it to come home.
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The wiki is incorrect (still). You can set the battery failsafe to RTL in the full parameter list. It works lovely. I have mine go into failsafe with about 4 minutes of flying time left, or about 25%. I also have a LiPo beeper on the batteries that will start beeping around the same time. Plus I have Mission Planner blabbing away about it I always try to make a point of landing or being in the area to land with that kinds of battery life left anyway. At which point I either let it land itself, or I takeover and enjoy the last few minutes and land myself.
With a single 5000mah 4S battery, I try to be on final approach around 13-14 minutes. With (2) 5000mah batteries in parallel, more like 18-29 minutes. But I find it flies better with a single battery (weight) so that's usually what I do.
Despite the abuse you suffered in this thread, I too have had the same issue several times. The configuration is correct, the threshold for triggering the RTL is 10.7 and yet this bird land hard and fast with no warning. The latest case MAY have been traced to a bad battery as it is now bloated and needs to be replaced. The other times, it was not the battery - no warning and it just lands wherever it is which is NOT good.
As a follow up, I found what appears to be a bug or oversight in Mission Planner on this matter. if you're in the failsafe settings screen, there is no option to select LAND vs RTL for the battery failsafe. The wiki page states that it will just LAND, and that it will only RTL if already in Auto mode.
However, if you go to the full parameter list and look at the battery failsafe parameter, there is an option for OFF, LAND, and RTL! So, it can do exactly what I want. I set it for RTL and tested it. It did indeed initiate an RTL when either the MAH setting or voltage setting was exceeded.
I would say the battery failsafe RTL when in Auto is not always the best solution. If you are in auto and pretty far from home location, a try to RTL (with a low battery) will fail.
Maybe is better the system to compute the time/resource to go to destination. If enough battery, then RTL, if not, Land.
This is exactly what I was I talking about before when it comes to calculate how far and how long you can go before launching. If you create an auto mission that exceeds your "available fuel", I would call that a user error.
However, if the battery becomes low due to a battery cell failure, that is not something you could ever predict or plan for. I think this is really a damned if you do, damned if you don't scenario. You could set RTL and if you're lucky, it will have enough juice to make it home. It might not make it and drop somewhere undesirable. Or you can set it for LAND, and it might arbitrarily land itself somewhere undesirable. If it dies completely during RTL, it's free falling to to the ground, which is bad and could cause damage or hurt someone. But at the same time, arbitrarily landing slowly with the blades spinning can cause just as much injury or damage.
There are inherent risks with everything we do in every aspect of our daily lives. Be responsible about how and where you do what you do, and mitigate what you can within reason.
The voltage you have the alarm go off at depends on your copter's design. We all use power at different rates. The rate at which you use power, and the capacity of your batteries will determine what your bingo fuel is. I like to have the alarms start sounding with about 4-5 minutes of fuel left. I also have the failsafe voltage / current set to initiate RTL at about the same time. At that point I either just let it do that, or take over and do it myself.
I use 5000mah 4S batteries running two in parallel (10,000mah). My average current draw is about 23-26 amps. Some simple math concludes that for 5 minutes, my bingo fuel is 2000mah.
Your results will vary based on all the usual variables. You can look at the "Battery issues log" after a flight to see where you power starts dropping off. As I'm sure you've noticed, it doesn't gradually decrease. It just tanks. So look for the point where where it tanks and subtract a few minutes. Note the current used and voltage at that point.
I learned not to leave to little time for an RTL last weekend. It reached the top of it's descent at about 100ft above ground. Then promptly ran out of juice and dropped from 100ft straight down. It was a precision uncontrolled on-target free-fall :). Landing skids took the hit without any damage. I was impressed.
Plug in via USB, go to Terminal, and click CONNECT. Click Log Download. Download whatever logs are available. They're saved to the computer. When done, close the log download window and click Log Browse. Open one of the logs you just downloaded. There will be a little dropdown with different types of pre-configured graphs. Select "Battery Issues". You'll see the voltage has a nice steady gradual decrease until about 12.8, then it just tanks.
When I was first setting up my current sensors (hall effect so needed changes to the code at the time) I suffered from an unwanted battery fail safe forced land. I knew that the sensors were not calibrated and reading too high but did not think it was an issue. What I did not know was that the fail safe was enabled and about half way through a flight the quad decided to land right where it was of its own accord - even though it had plenty of battery capacityremaining. This was most unfortunate as the quad was out over the harbour at the time. I was helpless as it descended into about a meter of salt water. Luckily there was very little current as it was quite murky and I could have lost it for good. As it was I had to completely replace all electronics. I think that we need the ability to take back control after a battery fail safe to avoid such problems. There are many instances where landing imediately may be a very bad idea...
You can retake control after the battery failsafe. Just toggle the switch on the RC Tx. Pretty sure you can send the command through MP as well.
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