I'm getting in on this late, but just wanted to say that the replacement compass is dirt cheap, AND they send you a new leg...no idea why they send the leg, but they do.
Compass Caution!
- Thread starter henryten
- Start date
The GPS knows where "you" are and the compass knows which direction you're (supposedly) pointing. So here's the scenario: What if the GPS knows that the vehicle is drifting and needs to move slightly north to maintain it's position. If the compass is messed up, the GPS may keep trying to move "north" but end up moving it south, based on the erroneous compass data.
That could lead to the weird behavior and even a flyaway.
Does that make sense?
Thanks for mentioning that.
I would point out that replacing the leg with compass involves disassembling the body and switching out compass connectors - not difficult, but intimidating for many folks.
Also, my problem compass was a replacement leg.
A GPS can give compass bearings as well, but only if you move. You'd have to walk with the bird for a short distance so the GPS can work out; "You were THERE, and now you're HERE, therefore you travelled in xyz direction".
It could then compare THAT to what the compass says, and work out if the compass is screwy. It could only do this while moving, but could do it.
It could then compare THAT to what the compass says, and work out if the compass is screwy. It could only do this while moving, but could do it.
The compass problem is measurable in Phantom Assistant. It's under the TOOLS tab, third line down is "compass(raw)." The "mod" box reading should be between -750 and +2250. (The question mark above "mod" is full of useful info).
I saw that demagnetize video - it's pretty vague, but it worked for me: wave a small magnet about 3cm from the compass. If you watch the "mod" box you can see the number fluctuating. I did many passes around, under, over - changing direction of the spin. Has anyone tried an AC degausser? - we used to use them to wipe video tapes.
BTW, I'm guessing that the whole thing is my fault - I may have been careless with a magnet around the P2V.
Good point. And that would explain the kind of "jinking" around I saw: GPS moves vehicle, discover the error and temporarily compensates.
Morning Gentlemen. I have the same exact problem henryten had. I was able to get rid of the red lights/low voltage/calibration failed alarms by repeatedly re-calibrating by getting dizy and also re-calibrating in the Assistant software. I took my P2V+ up and things seemed ok but not perfect. Now I'm away from home and she's all over the place. A steady hover is a thing of the past. I'll be back home in a few days and get things straightened out but I sure would like to send her out on a few missions. Do you think I risk a flyaway?
N017RW
Premium Pilot
I don't want to break up the good info you guys have been posting. But I wanted to toss something in that maybe nobody knew about, or has yet to mention it, but did you know the gps puck has a battery. And if that battery goes bad weird things may happen. The battery as I can remember is meant to over come hiccups with in the system. These hiccups happen often and without logged data that refreshes 250ms or faster you wont see it happening. The batteries are not replaceable either. You basically have to replace the puck altogether unless you find a replacement battery and solder. There is more details to know on this subject, but its one that I haven't posted about recently so I don't remember everything.
Also, another subject that needs considered in this thread is the pressure sensor and how it relates to the compass.
Forgive me now if I forget to follow up on this. I seem to be spending time that I always spent here but now in the P3 forum.
Also, another subject that needs considered in this thread is the pressure sensor and how it relates to the compass.
Forgive me now if I forget to follow up on this. I seem to be spending time that I always spent here but now in the P3 forum.
N017RW
Premium Pilot
Nah, it's the real-time clock and back-up ram battery.
It looks more like a super-cap (kind of like a rechargeable battery) cause it's spot welded into it holder like it's not intended to be replaced like you would a watch battery. You can Google it.
It's not even connected while the quad is running so it cannot be responsible for any weird stuff.
Anyways even if it goes flat it just means that every GPS start will be a 'Coldstart'. The type which takes the longest.
From the uBlox manual:
"In case of a power failure on pin VCC, the real-time clock and backup RAM are supplied through pin V_BCKP. This enables the u-blox 6 receiver to recover from a power failure with either a Hotstart or a Warmstart (depending on the duration of VCC outage) and to maintain the configuration settings saved in the backup RAM. If no backup battery is connected, the receiver performs a Coldstart at power up.
As long as VCC is supplied to the u-blox 6 receiver, the backup battery is disconnected from the RTC and the backup RAM."
Looks like you may have to make sure your Phantom is very level when you re-calibrate. And even then, you may have to do some tweaking.
http://forum.dji.com/forum.php?mod=viewthread&tid=4343&page=1
Perhaps worth mentioning.....
when you do the compass dance dont hold the quad by placing your hand over the top/covering the gps... otherwise it might go green but because your blocking the satts it will flash red leading you to think compass calibration failed....
best to hold it by an arm or something...
Caught me out when I first started doing it... so figured i'd speak up lol...
when you do the compass dance dont hold the quad by placing your hand over the top/covering the gps... otherwise it might go green but because your blocking the satts it will flash red leading you to think compass calibration failed....
best to hold it by an arm or something...
Caught me out when I first started doing it... so figured i'd speak up lol...
N017RW
Premium Pilot
????
That is not true.
How do you explain when it is held vertical for second half?
This is bad information.
Errr how its not true?
If you place your hand over the gps antenna... after the compass calib it will flash green and then flash red seems its lost satts....same as if you cover the gps at any other time?
Ive been able to hold the arm for both parts of the calibrarion.... to be clear I dont mean landing skid.. i mean the arm?
How are you not able to hold the arm for both parts... the thing wieghs like 1kg... ?
If you place your hand over the gps antenna... after the compass calib it will flash green and then flash red seems its lost satts....same as if you cover the gps at any other time?
Ive been able to hold the arm for both parts of the calibrarion.... to be clear I dont mean landing skid.. i mean the arm?
How are you not able to hold the arm for both parts... the thing wieghs like 1kg... ?
*cant edit on phone*
Hold it by 2 arms then lol....
Anyways pretty easy to proove this happens.... cover antenna when you do calib and at the END it will flash once green then flash red.... if you miss the green you might think its just doing red.
Hold it by 2 arms then lol....
Anyways pretty easy to proove this happens.... cover antenna when you do calib and at the END it will flash once green then flash red.... if you miss the green you might think its just doing red.
Can understand why you might disagree if you have only done the first half as it stays on permanant green during the second, until the end... if thats what you meam
N017RW
Premium Pilot
I
I see I may have missed your point. At first it seemed you were saying covering GPS would result in a failed compass cal. My apologies Sir.
Np I wasnt very clear. Should of mentioned 'at the end of the calibration it may appear as if failed'
Anywho moving on.
Anywho moving on.
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I think he means basically that DJI should fix the software so it ignores large changes.
Like if the compass is flipping N-S-N-S or if the gps suddenly thinks it's 2,000 miles away from where it really is, the software should be smart enough to know that the Phantom cannot fly 2,000 miles in 1 second, but it's not.
This is a simple software fix but it's just not happening for some reason. I'm sure there is tons of stuff going on behind the scenes that I/we are not aware of.
Like if the compass is flipping N-S-N-S or if the gps suddenly thinks it's 2,000 miles away from where it really is, the software should be smart enough to know that the Phantom cannot fly 2,000 miles in 1 second, but it's not.
This is a simple software fix but it's just not happening for some reason. I'm sure there is tons of stuff going on behind the scenes that I/we are not aware of.
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