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3D RoboticsPermalink Reply by Chris Anderson on April 27, 2012 at 7:40am

Did you calibrate your compass in the Mission Planner?

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Permalink Reply by Chad P on April 27, 2012 at 7:52am

I did enter/calibrate the "declination" but that is all I remember, would there have been something else?  THANKS for the help.

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Permalink Reply by Bradley J Carr on April 27, 2012 at 8:05am

Is the calibration something that needs to be done? Or can you put in the declination and it be good?

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3D RoboticsPermalink Reply by Chris Anderson on April 27, 2012 at 9:02am

It's best to do the "Live Calibration", too. The MP will instruct you on what to do.

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Permalink Reply by Chad P on April 27, 2012 at 9:59am

Chris, THANKS A LOT for helping.  I don't always get responses from the forums so I really appreciate it when I do.

I entered the Declination but I believe I did it manually.  I will try the "Live Calibration". 

Could (would you expect) the compass being off to cause the navigation control to send the plane further and further south on each circle?  Could that be my navigation issue or do you think they are two separate issues?

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Permalink Reply by Chad P on April 28, 2012 at 8:57am

So I ran the calibrate procedure a couple of time and got the compass to work better a little but never very reliably.  I think the magnets that are attached to the chassis and to the plane are throwing it for a loop.  It doesn't surprise me that magnets can effect a magnetometer, but what does surprise me is that other people aren't having this problem with the magnetometer and the Bixler chassis.  I do have an extra set on there so there are a total of 6 magnets on the chassis and 6 on the plane which lock together holding the chassis on very very well...but I guess by doing that I lose my compass.

Does the Magnetometer affect navigation in the way I described?  What effects will I notice with the compass not working properly?

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3D RoboticsPermalink Reply by Chris Anderson on April 28, 2012 at 2:18pm

I think a more likely explanation is that the prevaling wind at that altitude is towards the south and you need to turn up your gains to get more navigation authority. Did you load the Bixler config file? That should be a pretty good start, although it's always a good idea to go through this first-time process to tune the gains for your own aircraft.

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Permalink Reply by Phil Cole on April 28, 2012 at 3:58pm

You could try flying with the compass disabled. It should still navigate, just not in very straight lines, but it should hit the waypoints reasonably closely.

If the magnets are strong enough the compass will read pretty much the same no matter what the plane's orientation.

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Permalink Reply by Chad P on April 28, 2012 at 7:35pm

Phil, Thanks for the advice I may try that too. I did notice that my compass doesn't turn much at all.

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Permalink Reply by Chad P on April 28, 2012 at 4:22pm

Yea, the wind was blowing to the south and a bit stronger than other days I have tested (maybe 10 mph). I did load the bixler config file and read through the manual files but when the stock bixler configuration worked so well for FBW-A and Stabalize I didn't go any further with tuning and maybe I should. I did have a camera on there which would add a little weight but other than that it should be the same as every other Bixler with chassis and AMPv2.

What you suggest sounds very likely and I will look into "turning up my gains". I guess I got confused when the airplane kept circling. I guess I thought it would not circle but head straight towards a loiter point or RTL point if it got to far off due to wind or whatever.

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Permalink Reply by Chad P on April 29, 2012 at 1:18pm

Ok, so while on the ground for all of this testing...I tried the calibration procedure many times while APM was in the plane and got wildly different settings and no completely funtional compass results.

I took the APM out of the chassis containing the magnets and away from the plane with the magnets, ran the calibration procedure and got excellent results and responsiveness from the compass. I brought the chassis close again and the reading skewed without moving the chip and then was no longer accurate or very responsive.

So... I guess my first step is to remove the magenets from the chassis and hold it in another way as to not interfere with the electronics. My second step is to fly again and determine if my gains need to be increased in order to give more navigational authority.

The only question I still have is if the winds are to strong for my "gain settings" and I don't have enough navigational authority will the plane still circle and start drifting down wind while circling or will it turn up wind (towards the waypoint) but just not reach it?

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Wiki NinjaPermalink Reply by Gary McCray on June 16, 2012 at 5:00pm

Magnets or any large metal mass right by the compass will definitely make it unreliable.

When I move my Quad when its hooked up to my computer, I get a 15 to 20 degree skew when its setting next to the computer. I input the declination from my location using the web site and that works fine, but magnets near the "compass" in flight will absolutely not work and those little canopy magnets they use are extra strong high Gauss rare earth magnets.

I'll bet a lot of people are having this problem and don't even know it.

By the way there is one other possible cause of drift like you mentioned. If you have any trim on the roll or pitch sticks it will continuously displace the GPS point in the direction of the trim.

Because when in any auto GPS mode, the sticks move the GPS point not the plane so any trim acts as an offset which does exactly that.

It is imperative to set up your APM so no transmitter trim is required.

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