Airborne launch with very bad GPS signal

General
1

I am working on a project that involves launching a fixed wing UAV from a flying fixed wing aircraft. There is a Lua script that sequences the UAV through the launch process and does some initial maneuvering to get the UAV upright and flying. As the UAV’s GPS is unable to reliably get GPS signal while in the host aircraft, once flying, the UAV is put into CIRCLE mode where it holds barometric altitude while waiting for a good 3D GPS fix.

Unfortunately, while in the host aircraft, it appears that the lack of good GPS is resulting in bad attitude data and the UAV is unable to hold altitude in CIRCLE mode even when the Lua script over writes TECS_PITCH_MAX and TECS_PITCH_MIN to +/- 50 degrees. The logs show that the pitch estimate is up against TECS_PITCH_MAX while the actual pitch attitude is substantially nose down.

Because of the need to arm and launch without good GPS, I have set parameter to non-traditional values. I do not fully understand what some of them do and I am hoping that someone can suggest changes that would allow the ARHS estimate to function better during the time of very poor GPS so that CIRCLE mode can hold altitude until GPS and state estimates are good and GUIDED or AUTO modes can function properly.

I have attached the full parameter set.

Thanks in advance for any advice.

(Yes, I have tried searching for answers on this, but the results I get are not on topic)

log_20260423T084714.parm (25.1 KB)

2

My original question is still very relevant. However, I’m maybe seeing that at least part of the problem is loss of orientation when the system tumbles when deployed until it gains stable flight. I may also be looking for any suggestions to help the AHRS system recover as quickly as it can from a tumble? If I’m seeing errors in pitch in the area of 70 degrees, what conditions and for how long might be needed to re-orient? …still investigating…

3

Do you have any link between the vehicles? If so, you could try feeding GPS data from the host to the payload vehicle using lua.

1 Like
4

Good idea. A GPS re-radiating repeater is now providing a good GPS fix while in the host aircraft. We still need to see if that is enough to solve our problems.

5

That may work too.