Almost Crashed - RTH Learning Opportunity

[ElGuapo]

There are three types of RTH: Smart RTH, Low Battery RTH and Failsafe RTH.
Your Mavic was under the influence of Low Battery RTH. In this mode the aircraft will land automatically if the battery can only support the Mavic long enough to descend from it altitude but you can still us the remote controller to alter the Mavic's direction during landing.

It is important to keep in mind that the Mavic supports Dynamic Home Point meaning that the new home point is not from where the aircraft launched but it is set to the position of the controlller/mobile device.
You can easily change the home point to follow your controller before you launch.

Also in emergency situations you could use Combination Stick Command CSC to stop the motors, however this means the motors are going to shut off in mid flight and the Mavic is going to literally drop from the sky.

 

[cobra46]

@JohnC , in the example you give above, will the Mavic eventually shut off?

I have watched several videos of people hand catching Mavics, and I suspect most haven't take then time to turn off VPS (or claim they haven't). So how do you shut it off when you have a drone in one hand and a controller in the other?

As I mentioned earlier, my son did hand catch mine on my first flight of the day. It does behave like John mentioned. Pulling back on the stick will cause the power to be killed after a couple seconds.

This was not the case during my near crash.

 

[james_mav]

@JohnC , in the example you give above, will the Mavic eventually shut off?

I have watched several videos of people hand catching Mavics, and I suspect most haven't take then time to turn off VPS (or claim they haven't). So how do you shut it off when you have a drone in one hand and a controller in the other?

Hand catching is one of the reasons to use a Lanyard. The controller will hang from your neck which leaves one to catch & one to shut off the motors.

 

[maikm]

There are three types of RTH: Smart RTH, Low Battery RTH and Failsafe RTH.
Your Mavic was under the influence of Low Battery RTH. In this mode the aircraft will land automatically if the battery can only support the Mavic long enough to descend from it altitude but you can still us the remote controller to alter the Mavic's direction during landing.

The manual says about Low Battery RTH:

The low battery level failsafe is triggered when the DJI Intelligent Flight Battery is depleted to a point that may affect the safe return of the aircraft. Users are advised to return home or land the aircraft immediately when prompted. The DJI GO 4 app will display a notice when a low battery warning is triggered. The aircraft will automatically return to the Home Point if no action is taken after a ten-second countdown. The user can cancel the RTH procedure by pressing the RTH button on the remote controller. The thresholds for these warnings are automatically determined based on the aircraft’s current altitude and distance from the Home Point. ​

So, the battery level at which this is triggered is dynamically determined depending on the distance from the home point, right? And there is a ten second countdown during which you can take "action". That action seems to be hitting the RTH button, which I find confusing, because during Smart RTH (user initiated), it's the Flight Pause Button which must be used to cancel RTH. (In Failsafe RTH, it's the RTH button again.) I think it's not an ideal user interface that requires the pilot to recognize in an emergency situation which RTH mode it is and which button does what.

The aircraft will land automatically if the current battery level can only support the aircraft long enough to descend from its current altitude. The user can still use the remote controller to alter the aircraft’s orientation during the landing process. ​

So, that is apparently what happened in this particular case. All you can do is navigate to a suitable location and let it land there.

When the Critical low battery level warning is triggered and the aircraft begins to land automatically, push the left stick upward to make the aircraft hover at its current altitude, giving you an opportunity to navigate to a more appropriate landing location.​

Manual landing seems to be disabled at that point, which is an information that is not in the manual and which I learned here. Good to know. So if it really wants to land, and the indicator light is blinking red fast, you should really just look for a place for it to let it go down safely, direct it there, and let it do it's thing, right?

 

[JLane]

And there is a ten second countdown during which you can take "action". That action seems to be hitting the RTH button, which I find confusing, because during Smart RTH (user initiated), it's the Flight Pause Button which must be used to cancel RTH. (In Failsafe RTH, it's the RTH button again.) I think it's not an ideal user interface that requires the pilot to recognize in an emergency situation which RTH mode it is and which button does what.

I think you've mis-interpreted what the manual is saying, and I can see how it can be misunderstood until you've actually seen how it works. The part that says:

"The aircraft will automatically return to the Home Point if no action is taken after a ten-second countdown." - This is referring to the pop-up message you'll see on your phone. Before it initiates RTH, you'll have ten seconds to cancel it by swiping on your screen. Within these ten seconds, you do not cancel it by hitting the RTH button. (Although I can't say I've tried hitting RTH at this point to see what it does.)

then:

"The user can cancel the RTH procedure by pressing the RTH button on the remote controller." - This applies once RTH has already initiated (ie. you didn't take action within ten seconds).

 

[bandroidx]

That's only true if you select that option. The other option is that it will not shutoff the motor in midair unless it detects a fault, such as crashing into tree branches, then you can move the sticks together to shut it off.

My phantom 3 advanced landed upside down and burned out 2 motors trying to right itself. people on the dji forum said that the drone will not shut off with the stick in the corners command if its upside down. is it different on thr mavic?

 

[maikm]

I think you've mis-interpreted what the manual is saying, and I can see how it can be misunderstood until you've actually seen how it works.

I agree with what you wrote, but under Smart RTH the manual says:

The pilot can also immediately exit Smart RTH using the Flight Pause Button on the remote controller or by pressing the Stop icon in the DJI GO 4 app. ​

So it seems Smart RTH is completely different from any of the aircraft-initiated RTH modes, and is more like one of the other mission-like modes (TapFly, POI, ActiveTrack). Smart RTH should probably be considered a specialized form of a waypoint mission where the waypoint is your home point and a landing after that. Only then does it make sense to abort it with the Flight Pause button, rather than the RTH button which serves to abort all other RTH modes.

Or am I still misunderstanding this?

 

[JLane]

I agree with what you wrote, but under Smart RTH the manual says:

The pilot can also immediately exit Smart RTH using the Flight Pause Button on the remote controller or by pressing the Stop icon in the DJI GO 4 app. ​

So it seems Smart RTH is completely different from any of the aircraft-initiated RTH modes, and is more like one of the other mission-like modes (TapFly, POI, ActiveTrack). Smart RTH should probably be considered a specialized form of a waypoint mission where the waypoint is your home point and a landing after that. Only then does it make sense to abort it with the Flight Pause button, rather than the RTH button which serves to abort all other RTH modes.

Or am I still misunderstanding this?

My apologies, I misunderstood what I thought you misunderstood! haha So your confusion is regarding the Pause button vs the RTH button... Well I believe that in user-initiated Smart RTH you can use either of the two buttons to cancel. I admit that that I usually use the Pause button, but I seem to remember also being able to use the RTH to cancel it. I agree that consistency would be good, and I would hope that in any of the RTH modes, both the Pause and RTH buttons can be used to cancel it. It's quite possible that the documentation just isn't thorough enough. I'll certainly test this out the next time I have a chance.

 

[JohnC]

Yes it does after a brief burst of full power it shuts off!

 

[cmghoughton]

I've only have about 2-5 minutes to play and test out my Mavic but in my stupidity I did start to fly it in my home. I wanted to see how much more quiet and just had to play with it. It took off from my coffee table with out problems but when I was going to land about 30 seconds later I went to place my hand under it and catch it. I guess the ground sensors picked this up and it shot up to my ceiling, it did not want to descend. Luckily it missed my ceiling fan and I landed it on the table but I wasn't expecting it to elevate on it's own that quickly.
Sorry a little off topic, just thought I would share my stupidity LOL

 

[networth]

Today I hand catched and my VPS were too, but the mavic did not fly away from me and I simply switched off the motors in the air itself.

Now Im worried, isnt my VPS working :O

 

[Shuttershooter]

Here is an RTH question. Say your on a hill that is 120 ft above a valley and the Mavic is down in the valley. If you have the RTH altitude set for 30 meters, will it return at 30 meters above the valley or 30 meters above the RTH point? I would hate for my Mavic to slam into the side of the hill returning home

 

[maikm]

If you have the RTH altitude set for 30 meters, will it return at 30 meters above the valley or 30 meters above the RTH point?

That setting is always relative to the home point. The Mavic has no idea about the depth of the valley.

 

[jdcntulsa]

The landing behaviour of the Mavic is possibly one of the things that takes some getting used to. Under normal situations the aircraft will descend until it's 50cm from the ground, if you continue to hold the left stick down it will descend to the ground. Once this starts descending past 50cm if you let go of the left stick it will continue to land. Then shut down.

If you try to hand catch while it is decemding and the VPS sensors detect the 'ground' too quickly it automatically increases power in order to arrest the decent, if the ground continues to close in then it will increase power again to arrest the decent. So if it detects your hand approaching and you have the left stick held down it interprets this as a rapidly approaching ground and apples more power, if you now have a hold of it, it can't get away to provide more separation, so it piles in the power as it thinks it's about to hit the ground! Result is you have a hold of a Mavic that has applied full power to arrest its decent, in this case even with the stick held back it will apply a lot of power to arrest its perceived impact with the ground.

You can try this if you're brave descend to a hover put your hand under to catch it and then pull the left stick back, move your hand up and get a hold of it, the Mavic will try to accelerate away, it can pull quiet hard so be careful!!

Thank you JohnC this should help some of us. Added this to my notes. I have read or seen what you have said. Never all put together the way you have, everything comes together now. Like my lightbulb inside clicked. Ha. Nice post!


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[finalfantasyfans]

The best way to avoid Mavic fight back is to catch it after landing is engaged. Move Mavic above yourself and move your palm 2-3 feet below it and let it sense your palm. Pull the left stick down and hold it will then engage landing and it will slowly descends. When Mavic is descending, you can catch it or let it land on your palm and the engine will shut down.


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[m0j0]

Not sure who this question is directed to. I have not used my mobile as a return to home point but this isn't a bad idea.

My suggestion is you choose a takeoff location that is suitable for landing and leave it alone. Place it where you want it to return and allow it to properly record the spot for precision landing.. which means take off and let it hover long enough to take the required photos... then make certain RTH is set properly for your location. Then let it be... RTH Is incredible but most of the time I cancel it at some point and land it on my own. But if you chose a proper takeoff spot it should be fine landing on its own.


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[Pepermz]

Thanks for the sharing, very good points to take into consideration.