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Hi all, I thought I'd do a little write up on how I tend to use the log analysis function of APMPlanner.

I don't claim to be very knowledgeable about coding and such, being more of a engineering type I tend to use the graphs to understand what the software is doing, rather then trying to understand by reading the code. This approach may be good for other beginners like me.

The first example is used to gain an understanding of what parameters are used in loiter:

Let's use an example of a flight that contained one failed attempt at loiter:

 Graph the values from a NTUN line:  Long err, Lat err, nav lon, nav lat, Loiter lon I.

This will immediately identify the portion of the flight, where loiter mode was used. You can see that it begins around line 2000.

Zooming in on that part of the flight we get more detail:

RED and GREEN: How the copter is deviating from set position.

BLUE and PINK: how the copter is being commanded to move.

YELLOW: The state of the LOITER I TERM.

Here is the I term in more detail (YELLOW):

You can see that the I wind-up has deviated from zero.

NOW COMES THE KICKER:

In the forum you can see people asking if X version of Arducopter uses NAV in the loiter or not. Obviously, you have to know this, if you're going to tune loiter properly.

Finding out is as easy as graphing a NAV I TERM instead of the LOITER I TERM:

In this graph you can see that the NAV I TERM (YELLOW) wind-up does not deviate from zero,

hence this version does not use NAV terms or procedures for loiter.

A typical circling loiter:

This a typical circling loiter. The values being graphed are the same as in the last example, with no I term displayed.

 You can see that the commanded pitch and roll BLUE and PINK are a diverging oscillation which is almost perfectly in phase - this accounts for the circling motion.

You can also see that the position errors are growing as a function of the increasing control commands by the autopilot. 

Anyway that's enough for today, I hope someone finds my amateurish contribution useful...