P3A strange problem this morning... GPS-releated

[jimlips]

Took my P3A to do a Litchi mission this morning. Never got to even start the mission, as my P3A was acting strange, and I was lucky to get it landed OK. So that's why I'm posting the Litchi log here for some input from the experts.

I have never taken off from this location before - it is on a bridge, and, in hindsight, probably wasn't such a good idea. I figured it would give me better radio coverage, since it was elevated. But perhaps the rebar and other metal nearby caused issues? The first place (sidewalk) I tried to take off from said I needed to calibrate, but I had just done this yesterday, and within 5 miles of this location, so I figured it was due to the rebar. So I moved the aircraft into a more blacktop-covered area. That seemed to clear the alert, and the screen was green and said I was ready to go.

I took off, and immediately noticed that the craft would not hover. It acted like it was in ATTI mode, so I double-checked the switch on the side of the RC. It was in P mode, yet the aircraft was drifting like crazy. I concentrated on getting the aircraft back, and tried to land, but it just kept drifting. So I put it out over a dirt/grassy area, figuring I could crash it there, if things got bad. I was still mostly in control, so I "walked" it down about 75' from where I took off. Still on the bridge, but a little outcropping where there was more asphalt. I was able to successfully land there without too much trouble. Whew!

I'm posting my Litchi log, and hope that maybe someone here can tell me what was going on? And why my craft was drifting all over the place? Thanks!

 

[Fly Dawg]

I see at least part of the issue. You were in P-OPTI for much of the flight, low level flying with VPS on. Turn the VPS off . This is especially true in the scenario you described. At low levels the AC will drift and act strangely with the FC trying to confirm VPS altitude vs Actual altitude. I leave mine off and never use it. It causes more issues than it corrects. Just IMO.

 

[Meta4]

I have never taken off from this location before - it is on a bridge, and, in hindsight, probably wasn't such a good idea. I figured it would give me better radio coverage, since it was elevated. But perhaps the rebar and other metal nearby caused issues? The first place (sidewalk) I tried to take off from said I needed to calibrate, but I had just done this yesterday, and within 5 miles of this location, so I figured it was due to the rebar. So I moved the aircraft into a more blacktop-covered area. That seemed to clear the alert, and the screen was green and said I was ready to go.

I took off, and immediately noticed that the craft would not hover.
It acted like it was in ATTI mode And why my craft was drifting all over the place?

The bridge was steel or reinforced concrete (which is half steel)
The compass was trying to tell you that it had detected a large magnetic field associated with all that steel.
But the error message was poorly written and calibrating the compass wouldn't have solved anything.
Launching from somewhere away from the magnetic field was the only correct action.
Having a big compass error forces the Phantom into atti mode because the flight controller can't deal with the conflicting data from compass and GPS.
Your Phantom was in atti mode for most of the flight until 3:53.
Opti mode is atti mode + the VPS sensor. It doesn't use GPS input.
The VPS sensor would have had trouble locking onto anything if all it could see was blacktop.

The lesson from this is: Never launch from a steel or reinforced concrete surface.

ps. You shouldn't ever need to calibrate the compass unless you rebuild or modify your Phantom.
New locations or specific distances from last flight location are completely irrelevant.

 

[LarBear360]

The bridge was steel or reinforced concrete (which is half steel)
The compass was trying to tell you that it had detected a large magnetic field associated with all that steel.
But the error message was poorly written and calibrating the compass wouldn't have solved anything.
Launching from somewhere away from the magnetic field was the only correct action.
Having a big compass error forces the Phantom into atti mode because the flight controller can't deal with the conflicting data from compass and GPS.
Your Phantom was in atti mode for most of the flight until 3:53.
Opti mode is atti mode + the VPS sensor. It doesn't use GPS input.
The VPS sensor would have had trouble locking onto anything if all it could see was blacktop.

The lesson from this is: Never launch from a steel or reinforced concrete surface.

ps. You shouldn't ever need to calibrate the compass unless you rebuild or modify your Phantom.
New locations or specific distances from last flight location are completely irrelevant.

If push came to shove, can the AC be launched from an elevated platform over reinforced concrete such as a pool deck?

 

[Fly Dawg]

@LarBear360 ......Just wondered if you were going to say anything with the quote........LOL......

 

[Meta4]

If push came to shove, can the AC be launched from an elevated platform over reinforced concrete such as a pool deck?

The compass is right down close to whatever you place the Phantom on for launching.
Raising the Phantom far enough will make things quite safe.
How far is enough?
That depends on how much steel.
If it's just a small bolt that's right next to the compass, a few inches will be fine.
If it's a few tons of steel, it's going to have to be further away.

 

[solentlife]

If push came to shove, can the AC be launched from an elevated platform over reinforced concrete such as a pool deck?

The simplest and safest answer is No.

Blacktop ... I take it you mean ashphalt road ? Basically not a good idea as you have no idea what is under the ashphalt ... pipes / cables / all sorts ... maybe not quite enough to give an error - but enough to throw the compass of a few degrees and cause problem once airborne.

One thing I do if I have error shown when power up ... I do not just move to new location - I fully power down and then power up again at new location to make sure all errors are cleared ... I have found that just moving is not always enough and I have had some scary moments ... Now because I power down and then power up again at new location - even if only a few feet - I have never had a repeat of the problem.

Nigel

 

[LarBear360]

The simplest and safest answer is No.

Blacktop ... I take it you mean ashphalt road ? Basically not a good idea as you have no idea what is under the ashphalt ... pipes / cables / all sorts ... maybe not quite enough to give an error - but enough to throw the compass of a few degrees and cause problem once airborne.

One thing I do if I have error shown when power up ... I do not just move to new location - I fully power down and then power up again at new location to make sure all errors are cleared ... I have found that just moving is not always enough and I have had some scary moments ... Now because I power down and then power up again at new location - even if only a few feet - I have never had a repeat of the problem.

Nigel

Not asphalt; concrete pool deck. It is reinforced with rebar. I want to take a 360 pano of the pool and surrounding buildings, however, I'm reluctant to launch from the pool deck. I read somewhere launching from an elevated platform could potentially mitigate any interference. I don't think I want to risk it. I have decided to launch from the park across the street.

Thanks for weighing in!

 

[solentlife]

Not asphalt; concrete pool deck. It is reinforced with rebar. I want to take a 360 pano of the pool and surrounding buildings, however, I'm reluctant to launch from the pool deck. I read somewhere launching from an elevated platform could potentially mitigate any interference. I don't think I want to risk it. I have decided to launch from the park across the street.

Thanks for weighing in!

Its the 'cross atlantic' thing ... blacktop over here generally means ashphalt or tarred apron.

As to your Pool Deck ... yes - launch from a different location and then fly in ... but do not get so low that interference is picked up ... my observations are that if you keep to more than head height - generally OK. As you get lower - you can get strange things ...

I fully support your worry and not to try the elevated platform.

Nigel