Battery Failsafe didn't land - crash instead

During today’s flight I had a rather unpleasant experience with the battery failsafe:

I have mine with the standard configuration of 10.5V and LAND.

When the battery failsafe suddenly kicked in after a little less than 10 minutes in the air flying square patterns in AltHold mode at 10 m / 30 ft height. When my GCS told me that it switched to LAND mode, I used pitch to get IRIS closer to home, hoping that it initiate the altitude drop in the meantime. But it didn’t.

I could see the Quad coming closer and could see the yellow flashing light. But the altitude remained at 10 m / 30 ft. After nothing had happened for a few seconds I slowly moved the throttle down to force here to descent. Still nothing happened, even after reaching a throttle level of zero.

Now comes the moment where I made a stupid operator mistake: While not realizing that the throttle was still at zero, I changed flight mode to Stabilize, hoping to get her home safe manually. That’s when she plunged down to earth from 10 m / 30 ft height.
Nothing appears to have broken. Landed on a front arm, which got a bit mud on it. But I was able to have another unspectacular flight right afterwards.

Any idea why IRIS didn’t want to land? My expectation would have been that she started the descent right away after initializing LAND mode via the Failsafe. Out of a height of 10 m / 30 ft, it should have taken 20 seconds at the default 0.5 m / sec descent rate for the touch down.

So far I have only the tlogs. I need to open her up to get to the SD card for the other logs.


how long did you wait for it to descend before changing to stabilize?

Going through the tlogs it shows that there were 18 secs between the Failsafe initiating LAND and me manually going into Stabilize.
By that time it should have almost landed. But instead altitude didn’t change at all and remained at 10m.


I believe the manual states it hovers for 10s @ 10m before landing… I think this is for you to verify it can safely land there and/or take over control if need be to manually land it.

That sounds very interesting. Do you have a link for that?

I couldn’t find anything referring to that here: … LAND_SPEED

Looking at the tlogs of this flight from erickuhn19: viewtopic.php?f=48&t=6774
I can see that LAND was initiated due to failsafe at higher than 10m (about 30m). IRIS then descended to 10m, waited for 18sec and then descended the remaining 10 m.

Looks like I was too impatient. Yet, at the same time, in a battery failsafe situation I don’t want IRIS to linger for almost 20 seconds at 10m before taking another 20 seconds to land. That’s too long. What’s worse: I couldn’t force IRIS to start the descend earlier while being in LAND mode. That’s imho not right either.

And with the 3DR batteries, that drop voltage like crazy at the end of the flight, this behavior is just dangerous.

Do like the rest of us, change the failsafe to 10.7 for added safety

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