I’ve been having issues with the new hover throttle learn on my x8 spray drone. The symptoms somewhat resemble poor tuning with the throttle controller, as the drone abruptly gains and loses 1-2 meters of altitude (sometimes more) randomly.
Anyways, I was wondering whether or not this was due to the drone itself? There cheminals in the tank do slosh during flight, so could it be that throttle hover learn is not good with shifting CG. Should it be able to effectively handle constantly changing payload weights?
In my experience carrying either a liquid payload, or one that is swinging from a tether, it causes some instability - no different than a manned helicopter or airplane. I would recommend putting some baffles in the spray tank to prevent the load from causing a rapidly shifting CG.
Right, that’s to be expected… However, it flew fine before have throttle hover learn, so I’m curious as to whether or not it’s more sensitive to CG shifts.
Have a log with the example altitude excursions?
It may not be due to the learn function, and it may not be due to slosh.
Well, you should be able to set MOT_THST_HOVER to zero and see if it makes any difference. That disables the auto-learning of the hover throttle. And if does, then I’d say it could be causing the issue. However, it may not mean there’s something wrong with the algorithm. If your gross takeoff weight with a fully loaded spray aircraft exceeds about 70% throttle there’s going to be other issues with altitude, roll and pitch stability. Combine air currents with a sudden “slosh” to one end of the spray tank and the pitch or roll input required to maintain the spray track is going to translate to altitude change with a multi-rotor because the vertical thrust vector that should be available is now being used in horizontal vector to maintain attitude and ground track.
The other thing is that GPS altitude is not all that accurate. And a baro altimeter working with a spray aircraft in close proximity to the ground on a pass is not going to be all that accurate either. With current technology I wouldn’t expect to see sub-meter accuracy, and 2 meters is probably closer to reality.
Right, that’s to be expected… However, it flew fine before have throttle
hover learn, so I’m curious as to whether or not it’s more sensitive to CG