Sluggish Loiter / PosHold ok

Hi all,

I recently upgraded some copters from an early version of 3.4 to 3.4.5 or 3.5rc2.
Normally I fly in PosHold or Auto modes. For some AutoTune and config tests I used Loiter as a starting point as usual. Interestingly, on all copters loiter dangerously sluggish with slow overshots, while PosHold is perfect. This is definitely something new.

I follwed the advices in the manual at http://ardupilot.org/copter/docs/loiter-mode.html?highlight=loiter%20tuning:

Common Problems
The vehicle slows to a stop very slowly after the pilot releases the sticks (aka “freight train stop”). This can be resolved by increasing WPNAV_LOIT_MAXA (to perhaps 500), WPNAV_LOIT_MINA (to perhaps 100) and WPNAV_LOIT_JERK (to perhaps 4000).

But this did not help. Is there anything else I should try to adjust?
What is the most important value to fight such a behaviour - WPNAV_LOIT_MAXA, WPNAV_LOIT_MINA or WPNAV_LOIT_JERK?

Thanks in advance!
Thorsten

In case someone has a similar problem:
I did some more tuning of these values today and ended up with these values:
WPNAV_LOIT_MAXA 200
WPNAV_LOIT_MINA 40
WPNAV_LOIT_JERK 500

Increasing the values results in very slow but dangerous overshots.

I’ve also had problems w/ loiter in 3.4, and started using poshold instead. Same as you, loiter was very sluggish. If it started drifting some direction due to GPS, I could not overcome the auto command w/ my manual commands. no problems w/ poshold.

I’ll check the parameters you mentioned, thanks.

If you see some drift it is another story.
Loiter worked generally fine on my copters. But when stopping from WPNAV_LOIT_SPEED there were very slow but dangerous overshots. This is not related to GPS and I was always able adjust position manually at any time. So your issue must be something different.
If you really have a drift due to GPS you must be flying in an environment with high multipathing effect. This is dangerous. If it is not related to multipathing it might be interference, Also not really good.

It’s multipathing. I’m flying either for fun in the woods among trees, or for work in urban areas with tall buildings.

So I know exactly why it drifts, and can even predict how badly it will have issues depending on where I am (I’m getting quite a bit of experience w/ flying in bad locations).

But, it’s disturbing that if it’s drifting to the west and I give it full stick east, it only slows its drift to the west… It does eventually stop and start going east, but usually it’s run into something by then. (Or now that I’m used to it, I quickly switch modes and resolve the situation)

I have the same problem. Basically when I release the sticks, the desired velocity goes to zero very slowly and the copter drifts. I want to increase WPNAV_LOIT_MAXA, WPNAV_LOIT_MINA and WPNAV_LOIT_JERK but I’m afraid of too aggressive maneuvers.