Hi everyone,
I am experiencing a critical issue during hand-launch with my fixed-wing UAV(X-UAV Talon) and Pixhawk Cube Orange, I would really appreciate some insights from the community.
The Issue:
During hand-launches in Stabilize (and sometimes Mission/Auto) mode, the aircraft frequently suffers a violent crash immediately after leaving my hand. Instead of climbing, the aircraft rolls hard left straight into the ground.
The aircraft behaves inconsistently during hand launch.
Sometimes the launch is completely successful, and the aircraft flies normally for the entire flight.
However, on other flights, immediately after leaving my hand, the aircraft suddenly performs one of the following:
Rolls aggressively to the left and crashes.
Rolls aggressively to the right and crashes.
Pitches nose-down immediately after launch and impacts the ground before gaining altitude.
The failure happens within the first few seconds after release.
The strange part is that the direction is not consistent. Sometimes it rolls left, sometimes right, even though nothing has changed between flights.
Additional Observations
Another issue is that during successful flights in Stabilized mode, when I release the transmitter sticks:
Sometimes the aircraft continuously drifts to the left.
On other flights, it continuously drifts to the right.
Again, the direction changes between flights.
Log Files:
I have all flight logs (.ulg), CSV and tlogs and can upload them if needed.
Hi everyone,
Just a quick update: I realized the Google Drive link I shared earlier might have restricted access.
Here is the updated, publicly accessible link for all the files if anyone wants to download and take a closer look:
(I have also attached all the files, including the flight video, here if you prefer analyzing them in PlotJuggler or another tool).
Thanks again for your time and help!
Hi there,
After having a look, I believe its most likely an issue with the way you launch your plane.
With such low speeds after the launch, the plane stalls, which explains the aggressive rolling (the control surfaces also have no authority in this regime). This can also lead to the pitch down, depending on the uav specifics, like CG etc.
Personal recommendation - not facts:
You seem to throw the plane mostly UP when launching. This helps, because you get more time when its falling down to accelerate. But the video you shared already looks very scetchy.
I personally tend to try and give the uav more forward momentum, to limit the time its actively stalling. This also reduces the amount of height it will loose during the launch. In short: More forward, less up.
Otherwise, the only option will be to reconsider the way you launch the plane.
Drift issue:
I assume you are talking about the plane flying a turn. This is normal/expected in stabilized mode. To prevent this, use position mode (or attitude will also help). Stabilized mode does not compensate for things like wind, or build quality issues, for example if one wing has more drag than the other.
How much is the drift? And what does it look like?
Thank you very much for your feedback and advice. I will definitely keep the “spear/javelin” throwing technique in mind for future launches.
To answer your questions:
Stabilized Mode Check: I always check the Stabilized mode before taking off. Right before these problematic flights, I physically rolled and pitched the plane in my hands to ensure the ailerons and elevator were reacting autonomously in the correct directions. There were no abnormalities in the control surface movements prior to launch.
Sensor Calibration: As for the gyroscopes and accelerometers, I performed a fresh calibration for both of them at the flying field right before these flights.
Despite having fresh calibrations and successful pre-flight surface checks, I am still experiencing these aggressive, random-direction rolls and crashes upon release.
Did you happen to spot any other anomalies in the log files I shared that might explain this inconsistent behavior?
Maybe someone better than me can see something in the log files.
Sorry, all I have are some suggestions.
Forward motion is critical. There needs to be enough air flowing over the ailerons and elevators to work correctly.
I assume you are flying with a flight controller with joysticks.
I always fly in Spektrum ‘safe mode’. The amount of pitch and roll is limited. If I release the joysticks the plane will self-right. When I get into trouble, release the sticks and let it self-right.
Try to make it happen preflight. Perhaps you could do a very thorough preflight check. Mount it on a test stand move model and then the ailerons with the joystick and make sure they move correctly and smoothly. Make sure there are no bad spots in the servos. I’ve had aileron servo that worked smoothly until it got to a bad spot and it moved position suddenly.
Your flight controller (IMU) should be mounted close to the Center of Gravity. The model should have drawings showing this location.
