Trying to understand Fail-Safe Mode

[bhollis84]

OK, as I sit here waiting to here from DJI on my warranty claim, I am still puzzled as to what went wrong with my Phantom. I am 100% sure it was nothing done by my, and I don't mean that arrogantly, I just know I was extremely methodical and took every precaution before things went south.

Anyways, I am somewhat confused about the fail safe/RTH mode. I understand that the RTH feature will activate if the phantom is flown out of range, contact is lost with the RC, battery life gets to critical level, etc. But what I am trying to understand is more about the battery life. I know I had more than enough battery life when I took off, and the phantom was only in the air maybe 15 seconds before it went crazy and shot up in the air and then flew south and ultimately shut down and crashed. But, I've been wondering if it was some sort of battery issue that caused it to go crazy.

So let's talk theoretically here. If you were flying your phantom for quite some time and the battery got low... The phantom will go into RTH and come to the recorded home point and land. However, what if you were flying the phantom and it didn't have enough battery to return home... would it auto-land wherever it is? That is the part I don't understand. Not really relevant to what happened to me anyways considering my disaster occurred within 50 feet of where I was standing, but I am just trying to understand all this.

 

[Meta4]

Pages 28-9 of the manual should answer your questions on Failsafe and Low Battery issues

 

[erikgraham]

If the battery is low, you will get a message on your phone giving you the option to return home immediately. If its critically low, it will just land where it is. I don't recall off the top of my head where the dividing line is between "low" and "critically low" but I'm sure its in the manual. Probably 10%.

You can also reconfigure the default behavior in the Phantom Assistant app.

 

[bhollis84]

If the battery is low, you will get a message on your phone giving you the option to return home immediately. If its critically low, it will just land where it is. I don't recall off the top of my head where the dividing line is between "low" and "critically low" but I'm sure its in the manual. Probably 10%.

You can also reconfigure the default behavior in the Phantom Assistant app.

Exactly what I thought!! Thank you very much!

 

[RichWest]

So let's talk theoretically here. If you were flying your phantom for quite some time and the battery got low... The phantom will go into RTH and come to the recorded home point and land. However, what if you were flying the phantom and it didn't have enough battery to return home... would it auto-land wherever it is? YES, at about 15% battery That is the part I don't understand. Not really relevant to what happened to me anyways considering my disaster occurred within 50 feet of where I was standing, but I am just trying to understand all this.

You could have one or more of these issues to cause a RTH event. Battery at or below 30%, battery communication failure, controller fails to transmit, receiver fails to receive or 100% failure of a component input - Compass or GPS.

If you had a GPS failure, basically having 0 sat's shown, then you can have an event. The problem when you have a RTH and GPS signal is lost, the HomePoint reference becomes skewed Taking the craft to who knows where....last point recorded or last-last recorded...who knows. I bet you can't say how many satellites were received during the event....

If you where the one that had it drop from the sky while landing, then you could of had a poor signal from the battery. Making the RTH event turn into failsafe by landing where it was at that moment. If that was the case, it sounds like you had a critical component failure. I would suspect the IMU, no basis and just guessing.

I believe the phantom records a crash log, if it can... On my phone, within a DJI-Crash directory is a file dated for a crash event. It references java and numerical values, could be either phantom physical crash or a crash of the control system. Again who knows, don't care to understand... Check your phone for the directory and see if you have anything... does it match your event date?

Electronics, if they are going to fail, will fail within 30-50 days and software can have a glitch for a variety of reasons. I guess in our situation that could be better assumed by hours of operation. And when you step back and look at the thousands of components that make up the system, you can somewhat understand why things can fail.

Reading the manual and searching here on the forum will provide a lot of resources to your questions. You may find similar examples for what you experienced and even provide a resolve if one is needed. This will include all the Phantom 2 series for the example you posed, so use the advanced search page.

Good luck!

 

[Meta4]

If you had a GPS failure, basically having 0 sat's shown, then you can have an event. The problem when you have a RTH and GPS signal is lost, the HomePoint reference becomes skewed Taking the craft to who knows where....last point recorded or last-last recorded...who knows.

If your Phantom is getting less than 6 sats - that's as good as zero.
But if you lose GPS your Phantom should not be flying off to who knows where.
Without GPS it doesn't know where it is and has no idea how to get to home or anywhere else. It just drifts with the breeze in atti mode.
No big deal if it is in sight. Much more of an issue if it is out of sight.

 

[msinger]

Here's the setting in the Phantom Assistant that causes it to auto go home when the battery is low:


It's best to land before the battery gets to the low level. The next step is the critical battery level. And, there is no way to disable the auto land procedure that will occur with the battery reaches the critical level. If that kicks in, pray there isn't a tree below

 

[bhollis84]

Here's the setting in the Phantom Assistant that causes it to auto go home when the battery is low:

I understand that, I just was speaking theoretically....if the phantom didn't have enough battery life to go home, would it auto land wherever it was. Another user said that it would.

 

[msinger]

bhollis84, right, it'll auto land at its current position. You can supposedly give it full throttle at that point to move it a bit to a better landing spot (if you can see it). But, you don't want to adjust too much because the Phantom will drop out of the sky if it does not have time to land.

 

[bhollis84]

Which leads me to believe that I had some sort of faulty battery or something went haywire with mine that caused it lose power. Flew 6-7 minutes and landed, then took off about 2 minutes later and right after I got it off the ground it went nuts. Shot up in the air very high, flew south a little, then shutdown mid air and tumbled to it's death. Battery after crash showed 3 green LED's. But something went very wrong to make it shutoff in mid flight.

 

[RichWest]

If you had a GPS failure, basically having 0 sat's shown, then you can have an event. The problem when you have a RTH and GPS signal is lost, the HomePoint reference becomes skewed Taking the craft to who knows where....last point recorded or last-last recorded...who knows.

If your Phantom is getting less than 6 sats - that's as good as zero.
But if you lose GPS your Phantom should not be flying off to who knows where.
Without GPS it doesn't know where it is and has no idea how to get to home or anywhere else. It just drifts with the breeze in atti mode.
No big deal if it is in sight. Much more of an issue if it is out of sight.

You are correct regarding the GPS to ATTI mode, but in combination with a low battery event (real or otherwise), where does the bird fly if it has lost the correct reference to HP? Where the auto system believes it should be...

I recently experienced such an event, battery alarm (RTH) and less than 6 GPS, the bird went rocketing away from me... Even started an auto land attempt after the 50 yard flight. I stopped my recorder and recovered 6+ GPS and then was able to take back control after flipping the S1 switch. I had over 50% battery life as well, so the event put me into a panic not understanding I'd lost GPS orientation during the RTH event. FWIW, the battery read correctly after taking control...

Kind of interesting, after an event like the one expressed, I tend to think what did I do wrong and what could I have done to correct. Then figure out that the event was not my fault. A learning experience on how to recover from just about anything...