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Yaw Drift
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dutch445

United States
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these 30-40 mph winds the past few days have me thinking it'll be spring before I fly again!
just a couple inches down here in Madison County, although it snowed most of the day yesterday,
it didn't add up to much
2015-1-8
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dutch445

United States
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Hey Cory, here is a video i made of my drifting yaw,
i did it at a couple different heights, would you say
this was a  drift rearward and to the right?  hard
for me to tell....
http://youtu.be/k1XoTFRryBU
2015-1-8
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cory
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Looks more like a rear drift to me. So I would shim up the front with 10 sheets of paper and redo the IMU Advanced.
Its hard to tell looking through the birds eyes.... It would be beter to film the craft from the ground. I would have a better idea of which way its drifting...


2015-1-8
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dutch445

United States
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thank you Cory,
one thing I need to pay attention to that I did not earlier, is there is a chance
that I had the phantom sitting on a table and possibly some table cloth or
placemat could have been causing it to not sit perfectly level..  i can't remember exactly
how the phantom was sitting when i last did IMU calibration.  I will start with
a perfectly level calibration and test fly and go from there.

i am thinking i need to pull the top off anyway before i fly again, i want to document my
wifi module (with our without holes) and ESC versions.  While i am in there i will look at
the IMU and see if it looks to be sitting level also.
thanks again
2015-1-8
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Pmcdn2014
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cory@movecost.c Posted at 2015-1-8 10:42
Well F me.... Mine is spinning on a dime now.... I lucked out and stuck the right about of papers un ...

Question: If by recalibrating the IMU (which is believed to be off tilt in the quad itself) by slightly lifting what the internal IMU considers to be the low side is resulting in the quad yawing on a dime, then wouldn't that logically be causing the Phantom Plus to be fighting itself when trying to hover?  

I am not arguing your remedy to the yaw drift issue (I plan to recalibrate with paper stacks myself soon).  What I AM wondering is if the P+ has an unlevel IMU installed and was factory calibrated accordingly, then wouldn't it have then or after recalibration cause the phantom to think its hovering in an unlevel manner?  Does that make sense?
2015-1-8
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Pmcdn2014
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cory@movecost.c Posted at 2015-1-8 11:11
Jamie, my desk is level as well..I leveled it with a bubble level. I believe the V3's IMU are not 10 ...

I have a new Phantom 2 vision+ V3 that I got about 3 weeks ago.  I have not ever done an IMU calibration on it and it does drift when I yaw, FYI.

How would this factor in to the possibility of the IMU not being level from the factory?
2015-1-8
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Jamie Hellmich
Second Officer

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Okay Cory, here is what I have come up with.

I took the cover off the Phantom, and the IMU is way off level port to starboard, and high on the starboard side.  I laid a tungsten rod across the IMU, eyeballed for level, and it took 10 business cards under each of the port landing pads to get it the IMU near level.

So I put it back together and started stacking business cards under the rear and left (port) pads, calibrating and a test flight.  14 calibrations and flights to be exact.  Balancing between 15 - 25 mph winds, power lines, trees and my house to boot.

It appears to be pretty darn close at this point.  With the winds the way they are, I'm going to leave it here for now.  I tried GPS and ATTI modes, and it stays put in a nice easy pirouette,  which I deem a must for camera pans, and to get away from trouble when low and slow in tight places.

Here is what I wound up with for card counts under the pads:

LR - 19..........LF - 16

RR - 3...........RF - 0

So it only took 3 under the rears to eliminate the minor front drift, but my gosh, 16 business cards to raise the port side and stop the right drift.  As well the Phantom is stupid out of level.  A level from a port prop spinner to a starboard prop spinner has about a 1/4" to 3/8" gap at the starboard side.
It does fly and hover level though.

I don't know how, why, or what causes this to fix the yaw drift issue, but it has.   I can only assume that the IMU should be mounted level in the aircraft, and mine definitely is not.  And further, the shimming I did during calibration, definitely was in the direction of leveling the IMU the way it is installed.

It remains to be seen how this affects the other flight controls, hovering, stability, etc... And I'll be checking that out when these winds calm down.

I'm also not sure how DJI can send these out with the IMU that far off level.  Unless it doesn't matter, and shimming under the landing pads for IMU calibration is correcting something else.

Please weigh in with any thoughts.... Cory or anyone.

Jamie

Tungsten rod across IMU

Tungsten rod across IMU
2015-1-8
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cory
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My expertise definitely isn't flight dynamics...lol.. I'm familiar with GPS and helicopter gyros, but these advanced flight controllers are new to me.

My theory is there are multiple things that takes place during an IMU calibration. One of them is figuring out how level the craft is when it yaws. If the Flight Controller, Main Controller, whatever we call the IMU board inside is off kilter, then an IMU calibration with what we think is a level craft will be off.

I also have a theory that there are multiple programs controlling the flight. One of them is yawing in place, which requires a level Main Controller. Another program is running the GPS hold. Another program is running the course lock. I dont think these programs talk to each other. This is why I believe the GPS disengages during a yaw, and why it flies off course because of poorly installed Main Controller.

There are other videos on the net that support my theory. When flying in course mode before the magnetic declination fix, the craft would fly in an arch straight ahead of you. After you let go of the sticks, it would drift back on course because the GPS program kicked in.

I believe the quality control from DJI is lacking. This is why some crafts fly perfect out of the box (Like mine), and some have a drift. I bet my craft got some excellent quality control at DJI and they balanced it and compensated for their poorly installed IMU before putting it in the box. When I did the IMU calibration, I screwed up their balancing efforts. And thus started the trip...

On another subject, I did some flying today. Its windy down here, and I did have a little drift. But its 100x better than it was. I like the business card idea, and I will use that to dial it in even more perfect.
I'm going to open it up here soon and see if I have wifi holes, 2.1 ESC, and a level controller. I bet my controller is off level like yours.

I"m glad people are getting this solved.

sorry for any spelling or grammar errors, no time to check. Gotta run!
2015-1-8
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Jamie Hellmich
Second Officer

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I did some low to the ground and in tight flying this evening after a break from all the calibrations and "leveling".   It really does fly nice in GPS and ATTI.  I'm very comfortable now getting within a foot or so of trees, the house and such.  It will now spin in place and not go sliding sideways 10 or 20 feet away.

It's nice to not have my "you-know-what" all puckered up when flying within 30' of anything and wanting to do a spin turn.  I'm excited again about flying the Vision + V3 .

Mine has V2 esc's.  Wiring was all routed fairly nicely, and I didn't see anything looking like it needed any attention, except for the whompyjawed IMU.

I'm not sure what you mean about "wifi holes".  I'll google it.

Thanks for your help, and for starting this thread.  I had started writing up a post for this issue in a Word file to paste in at some point.  But just kept trying stuff on my own.  This is one of those times that makes forums as this shine.
2015-1-8
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cory
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The V3 wifi module should have tiny holes for ventilation.  I opened mine up, I have the 2.1 ESC and wifi holes.. So I'm good...

My Main Controller did not look tiled via eye, but did notice a  ferro magnet right up next to the main controller. I'm not sure I like that.
2015-1-8
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michael.haws
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Jamie Hellmich Posted at 2015-1-7 11:27
Cory, I'm with you brother.
I have this issue as well.  It should pirouette on it's axis as my other ...

My P2 drifts to the left when yawing and I am definitely going to try the fix described in this thread.   Now I'm beginning to wonder if this IMU miscalibration is what is also causing my gopro to roll slightly when the phantom is yawing.    Thanks Cory for posting this potential fix !!
2015-1-9
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Jamie Hellmich
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Michael,

Based on what worked out for me, if it is drifting or wandering left during a hovering yaw turn (to it's Port side), raise the right (starboard) landing pads.  It's trial and error as to how much.  I'd start with around 5 business cards if you have some, or other material.  Then do the IMU calibration, and a flight trial.

Same thing for fore and aft.  Shim up the opposite side/end of the drift direction.

Keep a record of the amount and under which pads they were placed for each trial with notes.   I did not to start with, and after 4 or 5 tries found it necessary to keep track of what I was doing.

If read my posts above, you can see it took a lot of shims to get it right.

I flew it a couple of times this morning and am very pleased with how it flies and maneuvers now.

I may yet contact B&H Photo and perhaps DJI to explain how far out of level the IMU is, and what I had to do to correct the flight characteristics.  I assume the condition and the actions I took are related somehow, but am not confident that the "fix" is the proper long term solution.  I still have several weeks remaining for a return to the vendor.

Jamie
2015-1-9
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dutch445

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i wonder if it's worth trying to loosen the IMU and level that inside the phantom
instead of shimming during calibration?
2015-1-9
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cory
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I think that would take more effort... It takes a good 10 tries to get it right, you'd have to put together the craft each time. However, your fix will be easier to do the IMU calibration in the long run. But these things are so sensitive that it will drift if you take away one business card...
2015-1-9
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Jamie Hellmich
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dutch445@gmail. Posted at 2015-1-10 02:35
i wonder if it's worth trying to loosen the IMU and level that inside the phantom
instead of shimmin ...

I had considered that.  But it is mounted to the board with double sided tape.  I don't want to mess with it too much as it's still "under warranty"/in the return period.

It may take leveling the board, but I did not look to see how to accomplish that.  I may look inside again this evening to consider that again.

If I had known that it would take the amount of shims it did take, I might have considered that at the time.
2015-1-9
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michael.haws
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Jamie Hellmich Posted at 2015-1-10 01:46
Michael,

Based on what worked out for me, if it is drifting or wandering left during a hovering yaw ...

Yikes,  just measured my table to make certain it was level and lo and behold it was not even close ... so I will start with finding a more level surface for my next calibration.
2015-1-9
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Jamie Hellmich
Second Officer

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That would be the prudent thing to do first.  Start off with an IMU calibration on a true level surface first.
2015-1-9
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drone
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cory@movecost.c Posted at 2015-1-8 10:10
I'm running an IMU calibration right now with a stack of papers under the front, so its unlevel as h ...

Cory thanks for posting this info. My bird also drifts in yaw after calibration. My bird does not sit exactly level because of the modified extended skids. It can rock back and forth just a wee bit. I never thought that was an issue until your post. My first level recal attempt produced better results. I have to admit I was a bit skeptical when I first read this thread but I am convinced. Good job on figuring this out.
2015-1-9
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jmtw000
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michael.haws@ya Posted at 2015-1-10 03:30
Yikes,  just measured my table to make certain it was level and lo and behold it was not even clos ...

Yeah, I'm having the yaw drift issue as well so I got my level and went looking for a nice level surface to calibrate on. It seems my entire house is not level
2015-1-9
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cory
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drone@jatobserv Posted at 2015-1-10 04:19
Cory thanks for posting this info. My bird also drifts in yaw after calibration. My bird does not  ...

Thank my OCD...
its a process to get it level, but once you figure it out its such a dream to fly. I just got back from 20 min of spinning in constent circles...
2015-1-9
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Pmcdn2014
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I decided to try this on my V3.  Mine seems to drift LEFT and back a little so I put some paper under the RIGHT side and did an advanced IMU calibration.  It helped a little but since the skids are basically like 4 points that the quad sits on, I decided to get a dinner plate (since it's round) and raise the front right part of the plate with the quad centered on it facing forward.  

I got very excited when I noticed that (after a few tries) it tightened up the yaw, but still was drifting left and rear, just not quite as much.

I went back in, added a little more (not measuring really) and it goes back to its original drift to the left a and rear.  Ugh.

QUESTION:  Those of you who have successfully corrected your V3 to where it's pivoting on a dime, did it take a lot of correcting and IMU calibrations until you got it tight?  

Also, whenever I've done an advanced IMU calibration in the past (on my Vision), it pretty much always warns me about it being hot, etc and how it should be cooled.  

Should I be letting the bird cool for a while between IMU calibrations?   Is this important or just a default warning?
2015-1-10
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Jamie Hellmich
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Pmcdn2014 Posted at 2015-1-11 02:07
I decided to try this on my V3.  Mine seems to drift LEFT and back a little so I put some paper unde ...

Here are my results from my post above:

"Here is what I wound up with for card counts under the pads:

LR - 19..........LF - 16

RR - 3...........RF - 0   "

These are business cards stacked under the 4 each individual landing pads.

19 business cards I used stacked amounts to about 1/4" high.  So it took quite a bit for mine.
2015-1-10
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steve
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Pmcdn2014 Posted at 2015-1-11 02:07
I decided to try this on my V3.  Mine seems to drift LEFT and back a little so I put some paper unde ...

Mine warns me about the cooling thing too. Even after coming in from a flight outside at -15C... Always seems to do it after a flight on the first attempt.

I'm at about 17 calibrations right now but getting very close.
2015-1-11
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Jamie Hellmich
Second Officer

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steve@huether.c Posted at 2015-1-12 04:43
Mine warns me about the cooling thing too. Even after coming in from a flight outside at -15C... A ...

I found that if you just exit Assistant and cycle the Phantom power, it will ask you to resume the calibration, and the rear LED's flash twice rapid amber every second or so, and did not repeat the heat message.

Yep, it took me around 14 or 15 tries myself.
2015-1-11
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Jamie Hellmich
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I'm still studying on this, there has to be another way to fix this drift without "falsifying level".

How much shim height are you at?
2015-1-11
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steve
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cory@movecost.c Posted at 2015-1-10 07:06
Thank my OCD...
its a process to get it level, but once you figure it out its such a dream to fl ...

Thanks for figuring this out!

I've got it working much better now. I think I did 21 total flights and calibrations. I would't say its perfect, but it stays within a 2 foot circle when yawing now and I don't think it was any better than that new. I've flown some low slow stuff around my yard and its much easier to control.

Pieces of paper:
FL: 18 FR: 4
RL: 12 RR: 0
2015-1-11
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Jamie Hellmich
Second Officer

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Good deal.  I know what you mean about much easier to control.
2015-1-11
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ddlugatch
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I'm having the same problem can anyone tell me exactly where I should put the papers, mine usually drifts to the tight about 4-7 feet after letting go of the controller. Was fine before I did a calibration. Its been drifting ever since.
2015-1-11
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Daninho
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Jamie Hellmich Posted at 2015-1-7 11:27
Cory, I'm with you brother.
I have this issue as well.  It should pirouette on it's axis as my other ...

i never tested it with me P2 H3-3D and i have it since 2013. It will depend on the wind i guess and if you are in ATT or GPS mode but i never needed  to pirouette on its axis.

I dont think it will be useful to level the desk with a bubble level, who knows how level the legs are and so on. you have to probably level the Naza itseff but i dont think this has anything to do with it. I calibrated the IMU before every flight and i bet my floor was not always 100% level and i would think the landing gear of the phantom is also not 100% level, its like injection molded stuff. Also the IMU will get decalibrated after every flight, you can see it in the naza data
2015-1-12
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michael.haws
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Daninho Posted at 2015-1-12 21:30
i never tested it with me P2 H3-3D and i have it since 2013. It will depend on the wind i guess and ...

Daninho,   what do you mean when you say "the IMU will get decalibrated after every flight" ?
2015-1-12
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Daninho
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michael.haws@ya Posted at 2015-1-13 00:02
Daninho,   what do you mean when you say "the IMU will get decalibrated after every flight" ?

the IMU data gets worse and thats why you have to calibrate it after xx flights. I mean you can calibrate it and look at the data and write it down and then after your flight its worse.
2015-1-12
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Pmcdn2014
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I am in the process of correcting mine.  I've made about 8 to 10 advanced IMU calibrations adjusting the cards under the skids.

OBSERVATION: when in a hover and the back of the quad is pointing to my face, if I move the left stick left (causing it to yaw counter-clockwise) it drifts around to the left and back, sort of in a circle.  When I push the stick to the right (causing it to yaw clockwise) it does the opposite, drifting to the right and circling right and back.  

So, it definitely wants to drift to the rear a little and to right or left, depending which direction I'm yawing it.  

CORRECTIONS SO FAR: I've been setting the quad on the table (where I did an initial Adv IMU Cali with no correction) and since been adding cards to the front left and right skids equally.  

I got it to tighten up the turn, meaning that it drifts to the side and back in about a 3' circle, which coming from what was about a 6' circle.  Always to the side I'm pushing the stick and to the rear, never front.

So, for fun I decided to go from about 10 cards under each left/right skid to 25 cards to see if if would cause it to yaw level or forward.  All that did was stretch the side and rear yaw drift dramatically, about 10' circle.

After that I put it back on the table and did another adv IMU cali with no cards and tested.  Back to a tighter, 2' side/rear circle yaw.

QUESTION: how come when I lifted the front of it much further (going from 10 cards to 25 cards under front skids) it didn't make it want to yaw level or push the yaw drift to circle forward?  I thought you lift the side of the quad opposite of the direction its drifting?  

Continuing the corrections and testing, but would like your input from those who are getting favorable results from their corrections.
2015-1-12
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disco4wd
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hi Cory, and thanks for starting this very interesting thread.
I've had my P2 V3 cover off recently to fit a mini iosd, etc. and noticed at the time what a sloppy job was done in the placement of the imu.
didn't think much of this until a couple of days ago I did an imu callibration and now finding the p2 seems to drift noticeably.
I have done several re-callibrations and still have the problem so I intend to try your method. It seems to me that if I spend quite a bit of time doing the paper/cards trick and get things right , whilst ensuring I try to get a level surface (and in exactly the same position each time) if for some reason I have to do this again in the future (and I am in a different locality) I thought that a good way to overcome this part of the problem might be  to place the quad on a base that is floating on water (in a plastic container :-) )  This should guarantee a dead level surface each time and not dependent on being in the same geographical location. Doing it this way, once one has worked out the number and position of papers/cards the first time (and recorded), these should not change if re-done using the water method again.

On a final note, none of us should be going through any of this bull if DJI were doing their job properly in the first place, and, if this problem does exist, they as the designers should know what is causing the problem and how to fix it without any of us having to wrack our brains trying to resolve their faults and provide remedies when we could be out enjoying the flying.
2015-1-12
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roger.allen
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Hi Guys!

I have exactly the same problem so have breathed a huge sigh of relief when I found this thread - believe me, I have tried everything too to try and fix this from changing CoG to adjusting gains and I have even left a support call open with the vendor in case I have to return the whole thing.

Anyway, unfortunately I lost a bit a patience and tried too much paper and the thing flew into a wall and I broke a propeller but I could clearly see that paper makes a difference as it crashed to the ground ;)

But I want to find a long term fix for this and I believe that means levelling the IMU. Unfortunately I can only get weekends to try these things. However I thought I would share an idea which I think might save a lot of time in the calibration process.

How about this? Put the phantom on a table, open it up and put a spirit level on the IMU, put your cards underneath the corners until the spirit level shows the IMU is completely horizontal. Place the lid back on so that the GPS is in the correct place and then perform the advanced calibration. Theoretically you should find the sweet spot first time.

If that works then I will definitely take the IMU off and level it myself at whatever cost so I can do calibrations in the future if necessary

Roger
2015-1-14
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bjr981s
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roger.allen@red Posted at 2015-1-14 23:05
Hi Guys!

I have exactly the same problem so have breathed a huge sigh of relief when I found this t ...

I believe that you are on the right track.

Obviously the factory can't place cards under the legs and test fly till all OK. The must have a fast way of doing this.

Removing the top of the Phantom and placing a small surface level on the IMU and then adjusting the model to level the IMU must be what they do in the factory. Anything else would be logistically too expensive.
And you need a surface spirit level not a normal unidirection level.

Cheers

2015-1-14
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roger.allen
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bjr981s Posted at 2015-1-15 01:19
I believe that you are on the right track.

Obviously the factory can't place cards under the legs  ...

ok, I opened it up and although the IMU is not flat, its stepped on two levels, I was able to balance a spirit level on it. I balanced it in all the directions I could by placing cards underneath the Phantom. Sure enough it needed balancing in the direction that I suspected. With the bubble in the centre of the spirit level I reattached the GPS and calibrated the IMU....

....I now have to wait until the weekend so I can take it into the countryside to fly it and see if this theory works...

Roger
2015-1-15
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cory
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Dont leave us hanging roger!!! lol
2015-1-15
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gnixon2015
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wow if you guys get this solution working, im terribly impressed. cant wait to hear the results!  this is one of the best threads this board has ever seen....
2015-1-15
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Jamie Hellmich
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roger.allen@red Posted at 2015-1-16 03:37
ok, I opened it up and although the IMU is not flat, its stepped on two levels, I was able to bala ...

I'm real curious too.  I'm still in the dealer return period, otherwise I would pull the NAZA unit out and level it in the craft.  You can see how out of level mine is in a picture earlier in this thread, and the shimming for calibration did go in the direction of leveling the unit.

After around 12-15 flights, I'm still good with the earlier calibration with no drift.  I don't see any issues so far with this fix affecting anything else negatively.

Jamie
2015-1-15
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cory
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After 20 or so flights myself, I'm very happy.
2015-1-15
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