Lost mine today, RTH failed.

[WetDog]

What I mean by the compass display is incorrect, my error ,sorry, the display on the app shows the orientation of the nose of the a/c , so if you point it due N as per your hand held it should show as being the same orientation on the display, hard to explain......, I sail, if my boat is heading N on the gimbal compass I check on my Silva occasionally just to check they are the same, you'd know if the display was more than a few degrees out. Thanks for clarifying about the start up in urban areas ,near trucks ,manholes etc: I bloody love this Forum ;-)

Compass calibration is perhaps a poor term. You are not doing a where-is-north calibration, you are looking to see if their are big enough anomalies in the magnetic field to temporarily confuse the sensor. It would be more like somebody walks in front of the compass on the binnacle with a piece of rebar in their hand - the compass will drift as the the rebar is moved closer or further from the rebar. To follow your analogy, you would have to be staring at the compass mod values on a regular basis while the Phantom is in flight. Except you have other things to do. Think of it as magnetic field calibration.

And I think Solar Diety is correct - SMART RTH (the calculation of how much power you need to get home) may be a one time per mission trigger. FAILSAFE RTH is something you can do all day if it makes you happy.

I do take exception to the wording in The Fine Manual.

I believe this incorrect, or at least incomplete: IF YOU SET THE RTH HEIGHT in the app before you fly, it will ascend to that value (not 20 m) when RTH is initiated. That value doesn't appear to be completely sticky. Although it seems to stay valid on power on sequences, something returns it to default values (firmware upgrades? - need to watch this).

The fact that this critical bit of information is buried under several menus and is poorly explained may be contributing to the problems we see here. I always check RTH height as part of my preflight setup. At 20 meters, I'm going to hit a tree nine times out of ten. I don't want to run into trees.

 

[Androne]

My forensic investigation yielded some new questions.
1 I checked my iPad and iPhone and both have RTH altitude and Max altitude set to 0! I believe this is because they are not connected to the craft but would like confirmation that they didn't arbitrarily reset.
2. The app is set to save video on my device but there are no saved video or stills in the DJI folders in my photos app. Is there somewhere else they could be saved on the device?

Thank you everyone for the awesome responses and help with this. I scoured the area where it could have crashed into a building if the RTH height was corrupted (and everywhere between) but can find no debris. Unfortunately there are many rooftops that can't be seen from any available vantage point so ironically, it seems I need a drone to find my drone!

 

[John Locke]

Smart RTH is when the P3 calculates how much energy the battery needs (+ reserve) to get back to the home point. You will only get this RTH once. If you cancel, it will not reactivate a Smart RTH from the battery level for the rest of the flight.

SD

I was thinking this might have something to do with this rth failure, but maybe not, as you point out. If the OP was on 1.5 firmware, or earlier, this failure may have been caused by sudden power battery shutdown, which as been known to happen on weak batteries coupled with high stress maneuvers that pulls a lot of current.

 

[snerd]

Meta4 has given the answer............... if you calibrated over the parking structure, and it took 3 tries because it was getting wonky readings, you took off with a bad compass calibration. Learn how to check the mod values in settings. It will give you a quick, general picture of the compass calibration.

 

[Androne]

I'm sure I'm betraying a bit of ignorance with this question but here goes. Why is compass calibration relevant when flying in GPS mode? I haven't looked at the compass in my boat since the day I got GPS. Wouldn't it just follow the shortest path to the logged GPS point (after ascending to RTH altitude) regardless of what the compass reads? The only reason I did the recalibration, aside from thinking I was playing it safe by following the app's suggestion, was because the app wouldn't allow the motors to start until I did a successful recalibration, which many are concluding was the cause of my loss. Snerd says, "end of story" but I remain unconvinced.

I appreciate all of the informed opinions here but if someone could steer me to a resource for deeper understanding than is provided by DJI videos and manual, I would appreciate it. I haven't yet decided to buy another one but I know I need to learn more before burning another thousand+ dollars. Thanks.

 

[Tallyrver]

I changed my RTH hight to 60m ,with the range of the P3 it could get far away before it lost signal. There are some tall trees around Tallahassee

 

[BudWalker]

I'm sure I'm betraying a bit of ignorance with this question but here goes. Why is compass calibration relevant when flying in GPS mode? I haven't looked at the compass in my boat since the day I got GPS. Wouldn't it just follow the shortest path to the logged GPS point (after ascending to RTH altitude) regardless of what the compass reads? The only reason I did the recalibration, aside from thinking I was playing it safe by following the app's suggestion, was because the app wouldn't allow the motors to start until I did a successful recalibration, which many are concluding was the cause of my loss. Snerd says, "end of story" but I remain unconvinced.

I appreciate all of the informed opinions here but if someone could steer me to a resource for deeper understanding than is provided by DJI videos and manual, I would appreciate it. I haven't yet decided to buy another one but I know I need to learn more before burning another thousand+ dollars. Thanks.

The GPS knows the current position of the P3 and the home position.The shortest path to the home position is distance and direction. The GPS doesn't understand azimuth information, i.e. it doesn't know which way the P3 is pointing. The compass is required to fly the P3 in a particular direction.

The GPS on your boat probably computes a direction from successive location updates coming from the GPS. Given two locations it's possible to compute the distance and direction. The navigation controller on the P3 can't work this way because the tolerances are much smaller than when controlling your boat.

 

[Trackman1]

Why is compass calibration relevant when flying in GPS mode? I haven't looked at the compass in my boat since the day I got GPS..

I have been wondering that myself. It would seem more like a backup in case of no GPS signal.

 

[Dirty Bird]

RTH is a convenient feature of the Phantom. When returning from a long mission it is a convenience. If you prefer not to use it that's cool but please don't decide for everyone that they shouldn't take advantage of the feature!

Why have people used RTH hundreds of times? I tried it once and never used it again. It is an emergency feature, not a button to use to simply let it come back. You should always fly back to your location under your own control.

 

[ianwood]

As @BudWalker stated, your GPS has no sense of direction. It knows where it is but not what its orientation is. It can compute a heading to a different location but it doesn't know how to get there. Any GPS navigation system beyond basic phone apps employ a compass for directional orientation.

And because of wind and other factors, you cannot reliably use GPS course over ground as a substitute for the compass.

 

[Meta4]

My forensic investigation yielded some new questions.
1 I checked my iPad and iPhone and both have RTH altitude and Max altitude set to 0! I believe this is because they are not connected to the craft but would like confirmation that they didn't arbitrarily reset.

RTH height is stored in the Phantom and not in the app.
It does stay there between flights but it's always worth checking stored app settings after a firmware update as some get reset to defaults.

 

[Meta4]

Why have people used RTH hundreds of times? I tried it once and never used it again. It is an emergency feature, not a button to use to simply let it come back. You should always fly back to your location under your own control.

Read the forums enough and you'll find quite a few threads from owners that lost Phantoms because they needed RTH and didn't know how it works and how to activate it properly.
Or others that saw RTH activate and when the Phantom began to ascend to RTH height, believing they were seeing a flyaway, initiated CSC and crashed their drone.

Not using the RTH features is a good way to not know how it works or how to initiate it properly when you have no other way to get your Phantom back.
I wouldn't make sweeping statements advising everyone how to bring their Phantom home, but I would make a sweeping statement advising every Phantom owner to try out RTH multiple times and experiment with it so that when they need it or if RTH starts up on its own, that they understand how to use it and how to cancel and resume control when necessary.

 

[wooglin]

RTH can only work if the RC and Aircraft can communicate. Hope you find it.

That is only accurate when you take off. RTH works if you turn your transmitter off completely, I have tested this.

 

[ITGuy]

Compass bearings are surely for 'our' benefit. A quadcopter can and does fly in any direction in its reference frame. Forwards, backwards, left and right are surely for our FPV orientation benefit. If the quadcopter is instructed to relocate to a different GPS point from its current position, i.e. to the left of its position, it does not need to know to 'point' in that direction it can simply move to it.

 

[egg1000]

Not sure if this offers any explanation. But reading previous posts and doing a bit of research I've found out wind speed (roughly) doubles at around 90m compared to 30m and (almost) triples at 120. So it's possible that if it was windy, whilst gaining altitude and indeed while attempting to fly back, it's simply not been able to beat the wind?

 

[Meta4]

Compass bearings are surely for 'our' benefit. A quadcopter can and does fly in any direction in its reference frame. Forwards, backwards, left and right are surely for our FPV orientation benefit. If the quadcopter is instructed to relocate to a different GPS point from its current position, i.e. to the left of its position, it does not need to know to 'point' in that direction it can simply move to it.

No ... the compass is critical to flying the Phantom. If it wasn't important, it wouldn't be on the Phantom.
Get a bad compass calibration and your drone is incapable of straight line flight.

 

[Meta4]

Not sure if this offers any explanation. But reading previous posts and doing a bit of research I've found out wind speed (roughly) doubles at around 90m compared to 30m and (almost) triples at 120. So it's possible that if it was windy, whilst gaining altitude and indeed while attempting to fly back, it's simply not been able to beat the wind?

Fighting a strong headwind can definitely be a serious complication for RTH.
Wind speeds may be higher at height - but they aren't always and there is no simple rule to show how much faster winds might be up there.
Your numbers seem way too high.

 

[egg1000]

Fighting a strong headwind can definitely be a serious complication for RTH.
Wind speeds may be higher at height - but they aren't always and there is no simple rule to show how much faster winds might be up there.
Your numbers seem way too high.

You're right, I was just about to edit my post.
Height of Wind Measurements Above Ground | Belfort Instrument
But look at the chart, should've compared ground level with 30m then 120.
Speed at ground level could be less than 10m/s
At 30m double and at 120 almost triple.

 

[Meta4]

Speed at ground level could be less than 10m/s
At 30m double and at 120 almost triple.

That chart shows a wind speed of 13 m/s @ 10 metres rising to18 m/s @ 100 metres
That's a small but significant increase but there's no doubling or tripling over that height range..

 

[egg1000]

That chart shows a wind speed of 13 m/s @ 10 metres rising to18 m/s @ 100 metres
That's a small but significant increase but there's no doubling or tripling over that height range..

Halfway between 6 & 8 is 7

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