GPS related flight modes apparently not working

[IanH]

Hi all,

I';ve recently replaced the APM2.6 on my hexacopter with a Pixhawk. Lots of faffing to get everything to fit but got there in the end. I';ve got it set up with 3 main modes: Stability, Loiter and RTL.

Starting off in stability mode and it flew pretty much perfectly. A bit of drift but I';m sure I can tune that out. However, when switching to Loiter it just dropped out of the sky (fortunately only a few of meters up over some heather so no damage done). Before take off it had good satellite visibility and position lock so GPS seems healthy. I';ve repeated this a few times and any mode that seems to require GPS doesn';t seem to function. I';m sure there';s probably a simple explanation for this but I';m a bit stumped. Does anyone have any idea what might be going (I might have done) wrong?

Thanks
Ian

[Paul-H]

Hi

I suppose the standard reponse is have you checked the logs, do the show an accurate altitude before switching to loiter.

Other than that not a clue, GPS would only be responsible for geographic position, altitude would be done via the Barromiter. IIUC.

Paul

[hoverfly]

As above I would check the logs first,them go to mission planner and check the advanced settings for baro and GPS.

[IanH]

I';m not completely au fait with the all of the logs (there are lots of abbreviations that I haven';t yet deciphered) but the barometer would seem to be approximately correct. Altitude roughly 2m which is about as high as I want to go and switch out of Stabilize mode as it';s going to drop out of the sky. GPS remains the same (I';d assumed that the GPS altitude, although not particularly accurate would have been used in the IMU positioning) so I guess that';s not the issue, especially if it';s not using it in Loiter mode for height. The only thing that seems to change is that the ThrOut value drops at the mode change despite there being no change in ThrIn:

[hoverfly]

Hmmmm trickey one , have a look at min throttle setting to maintain hover. Not very likely but check you have saved mode settings correctly  and the pwm output is not near another mode threshhold, try to get them in the middle of each range.

[IanH]

Thanks, I';ll check them later. Hopefully it';s a simple fix!

[Mslater]

Hover throttle setting will help, ensure radio is calibrated correctly.

Loiter uses mid stick (approx 50%) to determine height.  Check the logs for RC input on throttle channel and ensure it is 50% when in loiter to maintain height.

To set hover throttle, take off and hover at a constant height - then review the logs to see what % throttle was applied - use this as your throttle hover setting.