Can a faulty GPS module cause the drifting problem on Phantom 4 Pro? Drone is drifting east /or turning West in Autonomous missions

[timmydjr]

There has been alot of discussion and multiple threads on the drifting problem with a Phantom 4 Pro. I do 90% mapping so I noticed it when my drone was yawing in the flight (not drifting off course). When it was flying parallel to a street or long row of buildings, I noticed the further it went the yaw seemed to get worse and worse. The drone ALWAYS turns to the West. I read a thread that stated it was best to calibrate the gimbal with the drone leaning on the rears motors (camera looking straight up). After that I ran another mapping mission down a straight street and the same problem exists.

So then I tested by free flying the drone. I lined up over the street with the street dead center and directly north and south (literally and straight up and down on my ipad). Whether I flew north or south, the drone drifted to the east. And this makes sense because in the autonomous mapping mission the drone keeps turning to the west to counter the drift (I guess that is why it is turning to the west).

I have reset the drone. I have calibrated the Controller, IMU, Compass, Gimbal, and today I calibrated the Gimbal with the P4P leaned back on the rear motors. Today I also put new props on. This same drifting problem has happened to many P4P users and it seems absolutely crazy that there is not a solution or definitive reason why this is occurring.

I am wondering if a faulty GPS receiver could be causing this?? If not, could a failing or faulty motor/ ESC cause the drift?

Any help will be greatly appreciated.

 

[Fly Dawg]

I am wondering if a faulty GPS receiver could be causing this?? If not, could a failing or faulty motor/ ESC cause the drift?

You need first to do a detailed analysis of your flight logs from the aircraft. That will help in determining if there is an issue. If you have not reviewed the aircraft logs before, see the link below to retrieve them. If you need assistance with the analysis you will need to upload the aircraft .dat file to a sharable location such as Dropbox or Google drive ( These are usually large files ) and place a link back here and many of us can assist you with an interpretation of the data. See this link to retrieve the log files.

Retriev Aircraft Dat File

 

[timmydjr]

You need first to do a detailed analysis of your flight logs from the aircraft. That will help in determining if there is an issue. If you have not reviewed the aircraft logs before, see the link below to retrieve them. If you need assistance with the analysis you will need to upload the aircraft .dat file to a sharable location such as Dropbox or Google drive ( These are usually large files ) and place a link back here and many of us can assist you with an interpretation of the data. See this link to retrieve the log files.

Retriev Aircraft Dat File

Thanks Fly Dawg! Here is a link to the flight logs on Google Drive. When I opened up any of the logs for today in the Log Viewer, it did nothing. Not sure what I did wrong. Thanks again for helping with this!
P4P Drone A Flight Logs - Google Drive

The files are still uploading but they should all there there in a few minutes. FLY395 is the last file in the list.

 

[timmydjr]

You need first to do a detailed analysis of your flight logs from the aircraft. That will help in determining if there is an issue. If you have not reviewed the aircraft logs before, see the link below to retrieve them. If you need assistance with the analysis you will need to upload the aircraft .dat file to a sharable location such as Dropbox or Google drive ( These are usually large files ) and place a link back here and many of us can assist you with an interpretation of the data. See this link to retrieve the log files.

Retriev Aircraft Dat File

I did a better job of following instructions. Now the compressed .DAT file for the flights today are up on the same link post above. I will now download other flight days and put them up there as well. The flights for today consist of:
2 flights that were autonomous flights down a straight street using Map Pilot iOs app. The third flight was free flying where I am flying down the street to observe the drift. When flying with the controller it drifts to the east. When flying autonomous (any app) it will always turn/rotate towards the west during a north/south flight path. I think it is doing this to counter the Eastward drift ???

 

[BudWalker]

I did a better job of following instructions. Now the compressed .DAT file for the flights today are up on the same link post above. I will now download other flight days and put them up there as well. The flights for today consist of:
2 flights that were autonomous flights down a straight street using Map Pilot iOs app. The third flight was free flying where I am flying down the street to observe the drift. When flying with the controller it drifts to the east. When flying autonomous (any app) it will always turn/rotate towards the west during a north/south flight path. I think it is doing this to counter the Eastward drift ???

FLY395 wasn't in the compressed .DAT but I did look at FLY393. It shows the drifting that you've been talking about. I think this is the same problem where the P4P does an uncommanded yaw drift. Specifically, the P4P is attempting to reconcile a difference between the FC computed Yaw value and yaw determined by the compass. Take a look starting here

Phantom 4 Pro V2 Fell out of the sky...

Here is an example from FLY393 where the P4P was flow from south to north along the street.

Can you do an experiment? Let the P4P hover for 120 secs at the south end first. That should give it enough time to reconcile the Yaw/magYaw separation.

 

[timmydjr]

FLY395 wasn't in the compressed .DAT but I did look at FLY393. It shows the drifting that you've been talking about. I think this is the same problem where the P4P does an uncommanded yaw drift. Specifically, the P4P is attempting to reconcile a difference between the FC computed Yaw value and yaw determined by the compass. Take a look starting here

Phantom 4 Pro V2 Fell out of the sky...

Here is an example from FLY393 where the P4P was flow from south to north along the street.
View attachment 108766

Can you do an experiment? Let the P4P hover for 120 secs at the south end first. That should give it enough time to reconcile the Yaw/magYaw separation.

@BudWalker , do I need to let it hover for 120 seconds then run the same mission? This mission starts from the north end of the street. I just want to make sure that I am doing the experiment correctly.

I will go do it now and if I needed to do anything any differently, I will just rerun it. Thank you for your help!! I am hoping it can be determined what the faulty part is so I can just replace it

 

[BudWalker]

@timmydjr while looking at .DAT I noticed an intriguing

@BudWalker , do I need to let it hover for 120 seconds then run the same mission? This mission starts from the north end of the street. I just want to make sure that I am doing the experiment correctly.

I will go do it now and if I needed to do anything any differently, I will just rerun it. Thank you for your help!! I am hoping it can be determined what the faulty part is so I can just replace it

No, just do a single run along your street. But, let it hover first for 120 secs with minimal stick inputs.

 

[BudWalker]

@timmydjr while looking at .DAT I noticed an intriguing phenomena. You can see it in the plot that I posted. Seems there is a 4.5 sec periodic spike in both magnetometers, especially in Mag(0). It's best seen by looking at magYaw.

Do you have strobe mounted on your P4P?

 

[BudWalker]

I am hoping it can be determined what the faulty part is so I can just replace it

Sorry, but if my theory is correct it's not a HW issue. It's a Flight Controller issue that's not likely to be fixed. I suspect a trade-off has been made where the FC can reconcile some compass errors but at the cost of less than perfect Yaw stability.

 

[timmydjr]

Sorry, but if my theory is correct it's not a HW issue. It's a Flight Controller issue that's not likely to be fixed. I suspect a trade-off has been made where the FC can reconcile some compass errors but at the cost of less than perfect Yaw stability.

I ran one mission. I flew to the south end of the street and hovered for 120 seconds. The P4P rotated while hovering. I then ran the mission and the same problem existed. The log file has been uploaded to the same folder. Let me know if there are any other test runs you would like to see. Maybe flying North/South. Just let me know and I will go run it.

 

[timmydjr]

Sorry, but if my theory is correct it's not a HW issue. It's a Flight Controller issue that's not likely to be fixed. I suspect a trade-off has been made where the FC can reconcile some compass errors but at the cost of less than perfect Yaw stability.

I have another P4P and it does not occur with that unit. I even paired the controller from that P4P with this one that is rotating and the same problem occurred. So I really don't think it is an FC issue. I could be wrong but don't think so. If you want me to pair up the other FC with the problem P4P and do the same thing, let me know.

 

[Fly Dawg]

@BudWalker ...Was looking at a similar view. This may or may not mean anything, however if you also look at the mag direction of travel as well, especially in the wider view, there are data points missing in numerous areas.

 

[BudWalker]

@BudWalker ...Was looking at a similar view. This may or may not mean anything, however if you also look at the mag direction of travel as well, especially in the wider view, there are data points missing in numerous areas.

View attachment 108769

That's because the AC is hovering and it isn't travelling.

 

[BudWalker]

The new compressed .DAT only contains FLY403 which isn't an actual flight.

Just to be clear the experiment is to hover at one end of the street for 120 secs and then just fly to the other end. If you "fly the mission" then the stabilizing effect from the hovering will be gone

 

[timmydjr]

The new compressed .DAT only contains FLY403 which isn't an actual flight.

Just to be clear the experiment is to hover at one end of the street for 120 secs and then just fly to the other end. If you "fly the mission" then the stabilizing effect from the hovering will be gone

Tin4. I will go do that now. This time I will only fly to south end, hover 120 sec, and fly to north end of street. That is odd on the flight data. When I connected there was only one DAT file that had todays date so I assumed it was the flight record?? Going out to fly again now.

 

[timmydjr]

The new compressed .DAT only contains FLY403 which isn't an actual flight.

Just to be clear the experiment is to hover at one end of the street for 120 secs and then just fly to the other end. If you "fly the mission" then the stabilizing effect from the hovering will be gone

Hey Bud, I flew the one leg flight as instructed. After reaching sound end of road, I did not touch the sticks. Then before I flew it north, I raise camera and had center dead center of north end of road. After centered, I flew forward not moving any stick motion except forward. It drifted to the east about 75 feet over a 150-200 yard flight.

The log files seem a little confusing. I have uploaded all the FLY###.DAT files for today plus PARM and SYS file. When used DA2 to export the files, I selected what should have been the last flight, but it ONLY saved and compressed the FC file and did not include the AC file?? So to be safe, I then selected all files with todays date and used DA2 to save/compress them.

The very last flight is free flight, where I did as you requested.

Thanks a bunch!!

 

[BudWalker]

Hey Bud, I flew the one leg flight as instructed. After reaching sound end of road, I did not touch the sticks. Then before I flew it north, I raise camera and had center dead center of north end of road. After centered, I flew forward not moving any stick motion except forward. It drifted to the east about 75 feet over a 150-200 yard flight.

The log files seem a little confusing. I have uploaded all the FLY###.DAT files for today plus PARM and SYS file. When used DA2 to export the files, I selected what should have been the last flight, but it ONLY saved and compressed the FC file and did not include the AC file?? So to be safe, I then selected all files with todays date and used DA2 to save/compress them.

The very last flight is free flight, where I did as you requested.

Thanks a bunch!!

FLY406 seems to be the free flight you referred to. From what I can tell the P4P flew straight without any drifting like the previous flight. The aircraft heading was 15° at the beginning and flew straight to the other end. I suspect the gimbal was pointed 0° i.e. 15° left relative to the P4P X axis.

At time 48 secs the P4P arrived at the south end and began to hover. By about time 110 secs the Yaw had stabilized. At about 215 secs forward elevator was applied.

The path wasn't perfectly straight but it didn't drift. Yaw is shown as the green line emanating from yellow A aircraft symbol.

 

[timmydjr]

FLY406 seems to be the free flight you referred to. From what I can tell the P4P flew straight without any drifting like the previous flight. The aircraft heading was 15° at the beginning and flew straight to the other end. I suspect the gimbal was pointed 0° i.e. 15° left relative to the P4P X axis.

At time 48 secs the P4P arrived at the south end and began to hover. By about time 110 secs the Yaw had stabilized. At about 215 secs forward elevator was applied.
View attachment 108782

The path wasn't perfectly straight but it didn't drift. Yaw is shown as the green line emanating from yellow A aircraft symbol.

Maybe I am not using the right terminology. I edited your image. I used Litchi to fly from south end of the street to the north end. My gimbal is in perfect alignment. On the south end of the street I was dead center. Using Litchi, I had the gimbal cross hairs dead center of the north end of the street. Then I gave it forward stick only. No yaw, no left, no right. Forward only. But the drone "drifted to the right by ALOT. It should have ended up at the yellow dot but instead it was 75+ feet to the right.

If using autonomous software (pix4d or Map Pilot), and have it fly the same path, it will in fact end up at the yellow dot. But it is my theory that instead of the autonomous software applying "left" or "right" movement, it instead applies a yaw to correct the "drifting" that is occurring. And that is why the drone is turned a considerable degrees to the West by the time it reaches the destination point.

The drone will always "drift" (or what ever I should call it) to the east. The autonomous software will always "yaw" the drone to the West to counter the easterly drift. I hope this makes sense. Sorry if I am not describing this correctly.

Thanks again for your help.

Tim

 

[timmydjr]

Is it possible that a faulty compass could cause this behavior? I realize now that the GPS would have nothing to do with this but it would almost seem logical that a faulty compass could.

 

[BudWalker]

Maybe I am not using the right terminology. I edited your image. I used Litchi to fly from south end of the street to the north end. My gimbal is in perfect alignment. On the south end of the street I was dead center. Using Litchi, I had the gimbal cross hairs dead center of the north end of the street. Then I gave it forward stick only. No yaw, no left, no right. Forward only. But the drone "drifted to the right by ALOT. It should have ended up at the yellow dot but instead it was 75+ feet to the right.

If using autonomous software (pix4d or Map Pilot), and have it fly the same path, it will in fact end up at the yellow dot. But it is my theory that instead of the autonomous software applying "left" or "right" movement, it instead applies a yaw to correct the "drifting" that is occurring. And that is why the drone is turned a considerable degrees to the West by the time it reaches the destination point.

The drone will always "drift" (or what ever I should call it) to the east. The autonomous software will always "yaw" the drone to the West to counter the easterly drift. I hope this makes sense. Sorry if I am not describing this correctly.

Thanks again for your help.

Tim
View attachment 108783

The P4P was at the south end of the street at 176 secs when some aileron (green plot) was used to center it in the street. Yaw was 0°.

But, then at 187 secs rudder inputs (black plot) were used and the P4P responded by Yawing about 15° CW.

At 210 secs just elevator (blue plot)was applied and the P4P flew straight to the far end of the run.

The P4P doesn't turn into the wind to fly straight Rather it adjusts motor speeds to fly straight. E.g. wind coming from the left is corrected for by increasing the left motor speeds.

I'm still curious to know the origin of the magnetometer spikes I mentioned in post # 8.They haven't been evident in this last flight. Did you change something?