Servers by jDrones

Overshoot problem on left turn only

Hi all,

Im using Skywalker 1800mm frame euipped with Pixhawk Autopilot. During executing Mapping mission, the flight tend to overshoot heavliy when taking left turn, but seems very good on its right turn ( as illustrated in the picture).

What may cause the problem?

Tq

1 Like

@maam_13,
Please provide tlogs and/or dataflash logs to help troubleshoot your issue.
Regards,
TCIII GM

Without seeing a log I’d guess it’s either a mechanical problem with your control mechanism for left turns (control surface binding, servo issue, etc) or perhaps the wrong magnetic declination.

Sorry, forgot about the log file.

Telemetry Log:
dropbox.com/s/ux9ryom5g3tyc … .tlog?dl=0
Auto triggered at around 8.7% progress.

Bin File:
dropbox.com/s/v5l44iazj34555a/10.BIN?dl=0

Log File:
dropbox.com/s/4o2zidaptg87ji4/10.log?dl=0

KMZ File:
dropbox.com/s/63pv73w2y02lzmd/10.kmz?dl=0
Flight Path 6

Thanks!

Looking at your log it appears you have it set to autodeclination, so the compass is probably set OK.

Plotting your roll versus desired roll is very interesting, and to me rules out a control linkage issue. Have a look at the attached plot. A minus value is a roll to the left and a plus value a roll to the right. You can see the Pixhawk is requesting a left roll for a much longer time than the right. And your aircraft, as far as the Pixhawk sees, is supplying it. The actual roll tracks real well with the desired roll up to the limit of 45 degrees. If it were a control linkage issue you wouldn’t see the actual roll matching desired.

At this point and seeing this I’d say bad accelerometer calibration or even a bad accelerometer. Here’s why…When the Pixhawk wants a right turn it asks for it and your plane rolls to 45 degrees and quickly makes the turn. And when the Pixhawk wants a left turn it again asks for it, the plane rolls to the same (apparently) 45 degrees, holds it for a MUCH longer period of time, but per the track the turn isn’t nearly as sharp. This makes me suspect it isn’t really rolling a full 45 degrees to the left when asked. But since the Pixhawk thinks it has 45 degrees it just keeps holding it until back on course.

In other words, the Pixhawk says it’s seeing 45 degree banks in both directions. But the right turn is much sharper than the left while they should be about the same. So the Pixhawk isn’t measuring the left roll correctly. So redo the accel calibration and see if that helps. If not, then it might a problem internal to the Pixhawk.

Another way you’d see this problem is using FBWA or FBWB. I think both of these have maximum roll limits. Try right rolls and left rolls. They should be the same, but I suspect in your case they won’t be. I think you’ll find it won’t bank left to a full 45 degrees. But the Pixhawk will THINK it is.

Hi maam_13.
I had a quick look at your t-log file with mission planner. I am not an expert at analyzing logs but two things that I noticed right away were :

  1. The aircraft is almost never flying level. It is banking about 10 - 15 degrees left.
    [My first thought was this was due to the wind, but it does this in all directions of flight.]

  2. A vibration warning. The Z axis vibs are the worst.
    …also the compass EKF STATUS bar graph shows that there may be some problems with the compass. [could be due to vibrations]

So, the plane seems to need to bank left, (10 degrees or so), just to fly straight.
Is the flight controller mounted properly as APM plane wiki ?
Using stabilize mode ,does plane fly straight without using rudder or ailerons ? …and is this the same when flying with motor power or gliding with the motor off.
If there is anything large mounted on the exterior of the plane or if the plane is heavier on one side, it could be affected.
The rudder-trim and/or the motor thrust-angle could also be at fault.

The vibration is probably due to an imbalanced propeller and/or motor , or loose motor mounts or all three.
This should be checked right away because the vibrations will affect the IMU performance and possibly cause damage to the plane.

My first Skywalker ( the one with a foam tail-boom) was not straight and it wanted to turn left. I could trim it out, but the amount of trim needed changed with the airspeed, naturally.

The aircraft should be trimmed so that it flies really well in manual without using the flight controller, if not , the plane will not give you joy.

Regards
Chris

Hi… i’m having the same issue… Is hard to turn left in auto missions… but in fbwa mode everything is ok…
Do you have any tip?

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