[Paparazzi-devel] Quadrotor with Lia 1.1 - a sudden loss control authority after switching from Z_HOLD to ATT

[Michal Podhradsky]

Hi everybody,

we are testing a quadrotor with Lia 1.1. board and Paparazzi code v.4.0.3, using the adaptive throttle estimation for hover (as is in guidance_v_adpt.h)

During a flight everything went great until the RC pilot switched from AP_MODE_ATTITUDE_Z_HOLD (Z_HOLD with a barometer) to AP_MODE_ATTITUDE_DIRECT (ATT). At that moment we experienced a sudden loss of control authority over the quad (there was only a limited amount of authority, as is the NAV mode) and the craft started to rapidly descend (while staying stable). The full control was restored after roughly 15 seconds (where it was already just above the ground).

From the logs can be seen that the problem wasn't radio connection, and the AP mode was correctly switched to ATT. IMU, GPS, and barometer were also working normally. However thrust command from RC pilot seemed to be overridden by adaptive estimator, even though we were in ATT mode. A possible explanation would be a software glitch during switching the AP modes. 

Have you ever came across a similar issue (i.e. autopilot software glitch)?

Regards
Michal