Forward Flight Tracking Left

Byroman · Dec 22, 2013

Before I get started...
Man, I had a GREAT day flying my Vision with my local RC club. Some great video and pictures and lots of attention from the fixed-wing guys. I was down for about two weeks with camera problems...it was soooooo much fun having having my Phantom back!
Anyhow...

My Vision has an issue with straight out, stick forward flight. It tracks slightly to the left. Not enough for concern, but enough to make me continuously correct with very slight right input to get it back to a more straight forward orientation.
DJI indicates that this behavior may be a compass calibration issue. I calibrate before each flight and the issue persists (360 horiz...360 vert). Can anyone recommend where in the software I can make adjustments to the Vision or Tx to correct this - or is there further calibration I can perform within the software? Hell, maybe this is normal behavior...????

Any help or advice is appreciated.

EyeUpHigh · Dec 22, 2013

I see a similar issue and it's always subtle enough that I think that perhaps I'm not quite as aligned "straight ahead" as I thought. I might drift five yards off course for a hundred yard straight line flight and that's straight enough for most work... I've also recalibrated the compass with no change in tracking.

I suspect it's coupled to another odd behavior that I see - I can fly 'stick forward' in a (reasonably) straight line but when I let the stick go and the Phantom 'coasts' to a stop it always drifts left - sometimes by as much as ten or twenty yards if I was moving at a good rate of speed. I suspect it's an artifact of the hand-off from inertial guidance to GPS position hold but I have no insight to the inner workings of their software.

Do you see a similar drift at the end of a straight line run?

Byroman · Dec 22, 2013

EyeUpHigh said:
Do you see a similar drift at the end of a straight line run?

Yes, I get a drift as well when transitioning from forward flight to stop. Guess I hadn't really thought about the direction, but I believe it is left as well. It's like it's hunting for position inside a several meter radius. There was another pilot with a DJI F450 with GPS on board. His seemed a bit more stable in these situations, but I will admit he wasn't flying quite as aggressively as I was.

The thought that your tracks left makes me think it could be common. Lets see if anyone else chimes in.

Dcarter · Dec 23, 2013

Yes, drifting to the left in forward flight is normally a compass calibration issue.

Discussed at the 2 minute mark here;

http://youtu.be/2bxjL7wFyb8

Pull_Up · Dec 23, 2013

Another option is to put the Vision on the bench, be very pedantic that it's perfectly straight and level (put a long level across the motor arms in all directions, including diagonals) and run an IMU calibration from the Assistant software. Next time out in a suitable place do a compass calibration as well.

That should reset the IMU's "what is straight level" reference and should straighten things out as much as they are going to be. Any continued slight drifting after that it probably a "design feature"!

(I'm assuming that you've checked props for any nicks or dings that might be affecting lift on one side, or loose motor screws that could be doing the same).

EMCSQUAR · Dec 23, 2013

Pull_Up said:
run an IMU calibration from the Assistant software. Next time out in a suitable place do a compass calibration as well.

I found doing advanced cal from asst software, cal dance and making sure props are balanced eliminated any drift in GPS mode (except of course in high wind)

EyeUpHigh · Dec 26, 2013

Pull_Up said:
Another option is to put the Vision on the bench, be very pedantic that it's perfectly straight and level (put a long level across the motor arms in all directions, including diagonals) and run an IMU calibration from the Assistant software. Next time out in a suitable place do a compass calibration as well.

Put it on the bench today, leveled it (being a hobby carpenter I had a half dozen levels to choose from - trust me, that bird was dead flat!) and ran an IMU calibration. Then took it out to an open field and did the compass calibration dance. If anything the Phantom pulled left more than before - more likely I was more sensitive to the issue. Re-cal'ed the compass and still no change.

What's more annoying is now that I'm paying attention to it, I see that the Phantom pulls left about fifteen+ degrees when it's pointed straight ahead. I've been flying on a local soccer field and have been running the sidelines as an exercise since day one. If I point straight down the sideline the quad drifts left about ten yards by the time it gets to mid-field. To get it to track the line straight I need to point the Phantom fifteen or twenty degrees right - while it then flies straight down the sidelines on the video it's very obvious that the camera's not pointing in the direction of motion.

These are on days with no wind to a very light breeze. No matter what direction of travel, the quad always pulls left in flight and then runs a little "j hook" when I stop at the end of the straight-line run.

I've gone back and looked at videos from the past weeks and they all show this same tendency to pull left so I see now that it's been an issue out of the box. The props have been removed / installed a number of times so (you'd think that) any balance issues would have switched sides a few times rather than always favored one direction.

Unless everyone else who reads this reports that all Phantom 2 Visions behave this way I think it's time to contact the dealer. I've been wondering why FPV felt so untrustworthy, now I realize it's because when I press the stick forward the quad doesn't move in the direction it's pointed...

AHill · Dec 26, 2013

Is it possible the NAZA control module is not mounted exactly straight ahead? That might be a possible cause of it going left if compass is calibrated and gps is working ok. You also might try swapping props to opposite sides to see if that has any affect, eliminating props as a cause.

Driffill · Dec 26, 2013

If you have a smart phone on you while this is happening, try to dig up the GPS co-ord's of the area and check the magnetic declination to see if that may be throwing the compass off??

Other non phantom naza users sometimes need to turn the GPS puck to compensate for the area, with the phantoms compass mounted outside the GPS puck, it makes that method somewhat more difficult.

AHill · Dec 26, 2013

Driffill said:
If you have a smart phone on you while this is happening, try to dig up the GPS co-ord's of the area and check the magnetic declination to see if that may be throwing the compass off??

Other non phantom naza users sometimes need to turn the GPS puck to compensate for the area, with the phantoms compass mounted outside the GPS puck, it makes that method somewhat more difficult.

Could the compass be slightly rotated on the landing gear not matching the GPS puck?

Driffill · Dec 26, 2013

Ive read of people doing that, or using layers of paper /card to offset it. I've never had to do it myself so I can't say . . .

I just thought it mention that idea in here and let you guys youtube and google to see if it the same effect you are experiencing

Byroman · Dec 31, 2013

I was at the airfield again this weekend and had a buddy with a 450 Flame Wheel demonstrate forward flight on his quad - straight ahead full stick. His machine was tracking laser straight.
He said he was able to dial in 10° declination using his software to more accurately reference north in our area.
I read the other post about shimming the compass. Has anyone tried this yet or know if there is somewhere in the software to make this adjustment?

Byroman · Jan 6, 2014

Took my Vision out yesterday with the hopes of figuring out the left tracking and drifting issue. After religiously calibrating 4 different times, she was still drifting and tracking left - no change.

Then, in a moment of brilliance ( :roll: ) I decided to rotate the Vision in the opposite direction during calibration (I always rotate to the left, horizontally and vertically, only because that's the way Colin does it on the YouTube video). I'm not going to try to figure out why, but changing the rotation to the right WORKED!!!!

Oh man, straight flights are sooooo much nicer. I hope this works for anyone else with this issue. Chime in if it does.

Pull_Up · Jan 6, 2014

Interesting! Thanks for letting us know. Let the speculation as to why commence...

BenDronePilot · Jan 6, 2014

As some others speculate the control unit in your Phantom may not be installed correctly.. There is one thing worth mentioning though that even with a compass calibration it could still be off if the values are seriously out of range. Which would require running a magnet over the compass to degauss it followed by another compass calibration. It may be time to contact your dealer though at this point.

EyeUpHigh · Jan 7, 2014

Byroman said:
Took my Vision out yesterday with the hopes of figuring out the left tracking and drifting issue. After religiously calibrating 4 different times, she was still drifting and tracking left - no change.

Then, in a moment of brilliance ( :roll: ) I decided to rotate the Vision in the opposite direction during calibration (I always rotate to the left, horizontally and vertically, only because that's the way Colin does it on the YouTube video). I'm not going to try to figure out why, but changing the rotation to the right WORKED!!!!

Oh man, straight flights are sooooo much nicer. I hope this works for anyone else with this issue. Chime in if it does.

Sadly, I tried that last weekend and even with the counter-rotation during the compass calibration mine still tracks left by over 20 degrees. I've written to customer service at DroneFly looking for help but haven't heard back yet...

Pull_Up · Jan 7, 2014

I can't recommend this from personal experience, but I have read of people with V1 Phantoms and a similar issue loosening their compass module on the landing leg and rotating it slightly to compensate. Tighten, calibrate, check fly, repeat until the drift is sorted. You shouldn't have to do this (it's called correcting for magnetic declination) but might be worth a try (at your own risk)? If you put your location in here http://magnetic-declination.com/ it will be interesting to see if your local declination matches the drifting offset you're seeing...

Byroman · Jan 8, 2014

EyeUpHigh
There was one other step I forgot to mention that I performed in the field. I also tried to degauss (sp?) my compass several times. I used my cell phone to interfere with the compass as DJI shows here:

[youtube]http://www.youtube.com/watch?v=RFZs1FGntXI[/youtube]

I did this twice (the first time I had no result). And as I recall, the last time I performed it was before the the opposite rotation - maybe this was what actually helped!
Even though the video demonstrates this on a Flame Wheel - it should work the same for the Phantom. Have you tried this?

Byron.

Gizmo3000 · Jan 8, 2014

I might have to try the rotate-clockwise technique.
both my Phantom and F450 tend to fly a bit left
- and I initially set my 450 puck for magnetic declination as well in the first place.

Dazzler24 · Jan 16, 2014

Hi all, It's early days for me yet but I believe I might be experiencing the 'tracking slightly left' issue. Has anyone seen this reference from Naza-M pages? http://wiki.dji.com/en/index.php/Naza-M_GPS_Attitude_Mode_Flight
I've not made the adjustment myself but thought it might be worth mentioning here.
Cheers.