What would be causing this snaking?

Hi,

I had my first RTL flight this afternoon, which i should report did work, but the plane did not exactly take the shortest route home as can be seen from the GPS track. Started at the Flag and flew out on manual and then the red track is all under RTL.

This was using the SVN Ardupilot 2.5 from Sunday afternoon ( GMT )

I am guessing that i need to look at adjusting either the Heading P or I values. Does anyone have a suggestion as to what i should change first and by how much? your help could help to save me time at the field which has been bloody cold recently!

Thanks

#define HEAD_P .8
//4-1
#define HEAD_I .1
//4-2
#define HEAD_MAX 3500
//4-3
#define HEAD_MIN -3500
//4-4
#define HEAD_I_MAX 500setpoint
//4-5
#define HEAD_I_MIN -500
//4-6
#define XTRACK_GAIN .2
//4-7
#define LOITER_RADIUS 30
//4-8

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Bill Noyce February 16, 2010 at 9:40am

Thanks to everyone for their input. I can't believe that you were able to tell that a) i have an EM406 and b) i was flying into a small head wind! I hope you all feel as excited as me when you engage ardupilot and take your fingers off the sticks, which in itself is an odd sensation when the plane is still airborne!

I managed 4 flights today here are my observations.

First flight had an interesting wiggle, so i went back to manual and adjusted the rudder's trim, after landing and re-initialising ardupilot the wiggle had gone. The automatic detection of the Trims is great.

Dropping the Heading P value did make the heading corrections less responsive which at one point prevented the plane from returning at all. So I increased the values back to the original P = .8 and I = .1

Today it was noticeable that the EasyStar was flying faster and having much more difficulty with the altitude hold, but that is a whole different issue!

Have many people with EasyStars increased the surface area of the rudder?
Developer

Ryan Beall February 15, 2010 at 8:42pm

Something else to think about.....The gains are optimally scheduled based on ground speed so when you fly this tomorrow if the winds are different or a different ground track is picked (basically anything that will give you a different ground speed) your "lets go gain hunting" outing may prove to be trickier than you think. Just something to think about. The best way to find the best gain is to do a down wind upwind transition and then try to find the sweet gain that will preform well for both and then later schedule the gain higher for the lower ground speed and lower for the higher ground speed. You will see this in the 2.5.1 code.

gain schedule = (GS/Airspeed_cmd)*K_heading
Developer

Jason Short February 15, 2010 at 6:57pm

Is this with the EM406 or uBlox? Looks like the EM406. The next version will be better at estimating position and will help with the oversteer. Until then Ryan's solution will work.
Jason
Developer

Mark Colwell February 15, 2010 at 6:27pm

Congrats on first RTL flight !!
Bill Noyce February 15, 2010 at 11:00am

Thank you both, i will try again tmrw.
Moderator

Gary Mortimer February 15, 2010 at 9:51am

gains
Developer

Ryan Beall February 15, 2010 at 8:50am

gains are set too high. A good start is to take heading_I down to zero and probably cut heading_P in half.

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What would be causing this snaking?

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