This is a work in progress. I've tried to address some fine tuning and performance issues.

Denny R. had made a comment about the inertia of bigger props causing issues. I've added a low pass filter to smooth the positive acceleration of the props to see if we can get at this issue. It may require tuning up Rate_P for a few folks, but I saw little issue in multiple flights.

Crosstrack had a small math error that decreased the resolution of it. I've fixed that and upped the default gains to get better tracking. 

Made WP hit radius 1 by default. even 3m is too much for quads. (If you pass a WP you will move on to the next)

The Loiter method is tuned a little better by default, and now uses GPS offsets when flying less than 1.5m/s. Code experimentation will continue on this front. Thanks to Emile and afernan for their help!

A fix in the Z Accel startup was added to get an averaged result.

Added the ability to enter Loiter with Optflow enabled. - still a work in progress, not for everyday use just yet.

This alpha is on GIT now and is for user's who want to test code. As always, you need to use the "relaxpatch" version of Arduino you can find in the downloads section

Update: We've found and patched some small type bugs in the latest and updated some GPS drivers in the Library. Be sure to pull the latest code and check http://apm.tridgell.net/ for the status of each build run against the SIL sim server.

Update r3:

I pushed a version on to GIT that addresses a number of issues.

- the low speed GPS XY calculations were incorrect and have been fixed

- Nav_Rate I term has been removed in loiter control - it's too easy to get two iterms working out of phase

- A second derivative has been added to Roll and Pitch. I found it removed wobbles nicely - Can be adjusted in the planner as STAB_D with a default of .25 (just enough)

- Smoothing has been applied to the motor commands in a way that really quiets down the alt hold pulsing without much effect on latency

- Yaw now has a dynamic constraint and I've upped the yaw gain.

- The motors output now have an LP filter on them so that the accelerate just a tad slower than the deceleration. This is a test to see if it helps big Octo's and Hexa's

- The Rate_I term is now zero'd for first five seconds after takeoff to keep balance.

- Loiter gains are lightened up a bit

- Nav_Rate_P is lower to remove back and forth sped related hunting in loiter

- Compass is enabled by default

- New I2C Library now included which should solve I2C related lockouts

- optflow is still a work in progress.

Update R4:

This update is based on flights today in a very windy environment.

It occurred to me that we're handling the WP nav I terms incorrectly and I reworked the WP navigation to share the same I terms from the Loiter. Even though they use different error input, etc, they turn out to both deal with wind in the same way. I have not Flown WPs with this new code, but heavily tested it in the sim and It's really rocking in hard wind. Transitions from Loiter flight and Nav flight are very smooth. Please let me know if you have luck.

Update R5:

This is a quick patch based on a bad crash Marco had. My theory was an I term that built up during wind that needed to be reset, but wasn't. It's a corner case but It bit Marco pretty bad. Please re-pull if you have R4 running to go to R5. And please, please be careful. This is alpha code not for general testing, but for development. Don't fly it on anything you would feel bad about crashing. 

Jason

Update R6:

Includes fix for Acro mode reset bug.
I went through all of the global variables and gave them lengthy descriptions. It's worth a read if you want to learn more how the internals work. I'll be doing some more organization like this as we move forward with an architectural redesign for 3.0 \
This version is mostly clean-up, but does include 1 interesting performance enhancement. It's disabled by default because It's fairly untested. The idea is that the wind compensation created by the Iterms for lat and lon in Loiter and Navigation are carried over into Stabilize. This unifies all of the modes so that when you switch modes, you don't get a small, but fast change in pitch or roll. This is only noticeable in high wind environment. 
To get this to work, I look for near zero velocity and start moving the pitch and roll into the wind control items. This takes a  transformation from copter frame to world frame, but the result is the copter will hold the position against the wind with the sticks in the center of the controller. If you fly around the wind compensation will bleed off slowly - about 30 seconds.
Again, this is off by default and needs significant testing, preferably in the HIL sim first.JNL has already started and flown this version for real.
The feature may be off by default for another version or two, but just letting you know it's there.
I think it will go a long way to making the mode changes feel seamless.

Update R7:

Added an auto-land timer for RTL. If you don't change modes for 20s after the copter arrives at home, it will begin to auto-land. If you have failsafe and no GPS, you will immediately begin auto-landing.
Failsafe RTL now goes 10M up as it RTLs to avoid obstructions.
Added SIL test for failsafe. 

Update R8:

Minor tweaks and cleanup

Update R9:

Made climb rate controller for landing universal for all altitude changes

Update R10:

Updated Loiter controller - Works great in the sim, thanks Afernan.

Thanks,

Jason

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Do you want people to load it from Git, or will you be pushing it to the MP or a zip file?

Let's do GIT for now, then if it goes well we can do a ZIP.

Jason

Hi Jason, thanks for your new mods!

Line 115 of navigation.pde, check the name:

static void esitmate_velocity()

Same in ArduCopter.pde... esitmate or estimate? :-)

What are you edit ALT HOLD?  because , In .50 - 2.1 they are not same in ALT HOLD in .49....

Mornin',
So, who else has flown this? I flew two packs last night and manual/stabilized flight is good. But, that's not where the serious changes were. I'd like to know if anyone else tried to loiter... I did. :). I recovered by switching to stable, but as soon as I switched to loiter, the quad was literally out of control...
I'm off to appease the other half with a trip to get pancakes, but will test again in a couple hours with the basics- complete reset, etc..

Just FYI, same results. Loiter is unstable in flight after a reload and re-setup. Seeing if I can suss this out.

Quad makes rapid corrections along each axis to about 30deg. Increase LOITER_I again?

John, post your log here if you want.

Cool- have a look. It's only MP logging at 1hz. Lots of dead time in this log, but you'll see an event at each loiter entry. (APM 1280)

Attachments:

I had pretty much the same result too.

I was using a standard 3DR quad on a 4S pack and APM2.

Stabilize was somewhat undamped in response to step inputs, so I reduced the stabilize and rate P gains until it was fairly smooth, even a bit lethargic, in response to sudden stick inputs.

Loiter behaviour after this was still the same. I didn't leave it in Loiter for more than a second or so, enough for two oscillations. Maybe it would have just pitched and rolled ±30° or more and held in place, maybe not.

Second log mostly shows me tuning the Stabilize mode. There are about 5 attempts at loiter in the first log and two in the second, one after the tuning was done.

I'm used to a 1280 without logging, so I forget to clear the on-board logs of it sitting on my floor at home before I flew it, so I only have the tlogs with flight data in them.

Attachments:

Phil, yes, we're going to have to issue some new default PIDs for APM2. It has totally different sensors, so it will need a different config file with different default settings. Please give us a few days to dial in some good starter settings and we'll post that in the manual. 

uploaded the wrong 2nd log. Here's the right one.

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So the 2.1 release (with the videos) was not APM2?

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