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Loiter PIDs

Posted by Jason Short on October 5, 2011 at 11:18pm

I built a quick sim today to look for the optimum PIDs for Loiter:

What's looking good is

Loiter_P = .5 or .6 (more = some overshoot, but not much)

Loiter_I = zero (Just say no)

Nav_P = 4 (Higher than I thought, What will it do to navigation?)

Nav_I = .25 (Higher than I though, but still large like it should be)

Let me know if anyone proves this out!

Jason

http://wiki.ardupilot-mega.googlecode.com/git/images/copter_wp.swf

Here's why Loiter_I is a bad idea. It just ends in overshoot.

Here is Loiter_P from .5 to 1.8 (lower looks better)

This is Loiter kp 1, Loiter kI 0, Nav_kP 2 through 10, Nav_kI .2

Here it is in action:

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Replies

Amit November 20, 2011 at 4:54am

on the 93 version, NAV_LOITER_I = 0 and its still overshoots, the must be a finer range parameters
Todd Hill October 13, 2011 at 6:59am

flew four waypoints last night. After hitting #4 would not RTL. Planned new mission with two waypoints, same thing. Attempted auto takeoff, copter speeded to waypoint 1, i flipped to stabalize but couldnt recover. throttle was set at minimum (my fault). flying Y6 with 750kv motors, running 2.0.47. stabilize great, alt hold so so, loiter radius too big and fast.

2011-10-13 12-34 1.log

2011-10-13 12-34 1.kmz
Martin Szymanski October 11, 2011 at 6:00pm

There can be integral windups.

This occurs if a disturbance such as a wind gust occurs and the steering pressure against it cannot overcome to reach a waypoint. I am not sure of the pid method used with the arducopter. I presumed that the Imax is the limit that stops integral windup?

Here is a video if two different pid methods.

The disturbance would be interpreted as the wind pressure in the copters case.

http://www.online-courses.vissim.us/Strathclyde/WindupMovie.wmv

http://www.online-courses.vissim.us/Strathclyde/WindupMovie.wmv
Owen Booth October 11, 2011 at 2:31am

Hi Jason, I don't suppose I can get you to answer my question at this post?

Sonar attitude compensation

Thanks man, your work is awesome, and we all appreciate your efforts

regards,

Owen
Martin Szymanski October 8, 2011 at 8:56pm

There were some great flights today under Auto mode.

Integrals on both Nav and Loiter were set to .001 There was no wind.

What I observed was each time the copter began its approach to the next waypoint once it hit the maximum speed it rolled back to a stop. Then forth again in a wave like motion. Once at the derived waypoint it stopped pointed to the next waypoint with the same approach speed going up and down. Is there a derivative toward the speed m/sec, mph? The waypoint distances are small 100 m point to point. Possibly the GPS is not accurate. However i've found a garmin handheld accurate with groundspeeds. Also the IMU had to be rebooted after configuration changes were sent from MP otherwise the sonar was disabled. Attached is the log done today. MP 1.0.79 w Arducopter 2.0.46

Flying with no wind is enjoyable.

2011-10-08 1.log

https://storage.ning.com/topology/rest/1.0/file/get/3692282751?profile=original
Amit October 8, 2011 at 10:18am

On the 47 ver i have set the compass to the north, but when i rotate it 180 to the south there is 20 deg differences for the real south.

Any clue?
Balloon October 8, 2011 at 2:32am

Jason,

It have problem last code 2.0.47 . when i will change mode (ALT or Loiter) and I change back to Stabilize mode. I can't Throttle control and slow down on ground (No crash). and I down throttle and up again. I just normal control. Now it's problem about throttle when I will change mode to ALT or Loiter ..... Edit Now!! Please........

thank you , Balloon
Developer

Jason Short October 7, 2011 at 10:53pm

I updated the simulation to include all of the PIDs, motor Kv, and thrust.

It's a bit of a hack, but seems to work well.

enjoy

Jason
Heino R. Pull October 7, 2011 at 6:22am

I tried (2.0.46) Loiter_P=.6, Loiter_I=0, Nav_P=4, Nav_I=.25 last night in 9 to 10 mph gusty winds and performance seemed pretty good, but it got dark too quickly to really flesh it out. I noticed much less oscillation about the set point though and the log definitely look better.

I flew multiple flights (10 or so) at dusk earlier this week (Monday, Tuesday, Wednesday) with no wind (much better weather) before your sim came out and tried varying Loiiter_P and Nav_P with chn 6 but never got above 3.0 for Nav_P and below .9 for Loiter_P and always had some oscillation. Your sim is very much agreeing with what I saw and it is really helpful. Now I have a better feel for the parameters and I will be out all day on Saturday in the wide open spaces to flesh out - although the wind forecast is creeping up to 10 to 20mph for Saturday.
Brian Donovan October 6, 2011 at 1:50am

Thanks Jason

I think this is exactly what I want to start.

Problem is night time now and rainy. Hopefully tomorrow early I will have a go at this and advise.