Strange Yaw Behaviour

ArduCopter Copter 3.5
1

Hi there,

I am in the process of tuning my latest build and am seeing strange yaw behaviour that I don’t understand - looking to see if anybody has faced similar things and has an idea?

For context, it’s a very large Octo (14kg TOW, 24x7.9 Props, T-motor Flame ESCs and T-Motor 701S Motors (@12s). Roll/Pitch Performance is flawless and extremely responsive and smooth and the bird is very stable in the air - I am very pleased with it. All axis have been autotune, incuding Yaw, on a light wind day.

Yaw response to pilot input is very sluggish. It feels like “delayed response”, i.e. I move the stick halfway or more to left or right and the bird sloooowly starts to turn and picks up yaw speed gradually. But it happens so slow that I typically let go of the stick way to late because I want it to turn faster. When I do finally let go it continues turning and slooowly decreases yaw speed until it stops turning again a few secs later.

I think the following pic shows it nicely:

image
image.png1820×452 9.06 KB

Is this simply a matter of running another Autotune on Yaw?

I’ve done a few builds (not this large) and never had such sluggish behavior :frowning:
I need this to be “snappy” on yaw too…

Log is attached…

Thanks for any helpfull comments,
Christian

2018-04-15 17-06-07.bin (1012 KB)

2

Are you using Pixhawk 2.1? I have had a similar issue after switching my octocopter from the Pixhawk 1 to the 2.1 version. From my understanding the PH 2.1 is over sensitive for large platforms and the autotune parameters can be way off. You may try manually changing some of the parameters based on previous autotunes that worked well.

3

I have the same sluggish feeling on yaw after ugrading to 3.5 my Hexa, even setting Yaw Pid to very high values do not change a lot .

I’m using a standard Pixhawk not a 2.1

I wonder is this behavior is related to some EK2 esotericism

4

The problem is your ATC_ACCEL_Y_MAX parameter. It’s set to 1000, which reeeeaaaally slow. You could probably increase it by a factor of 10 at least.

The Accel parameters are tuned by autotune, but are often overlooked by users. They control how quickly the drone is allowed to increase its angular velocity, so it has a big effect on how the copter feels to fly, and excessively low values will feel sluggish.

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