AC3.0 CompassMot Setup

Demonstration of how to set-up compass motor interference compensation with ArduCopter 3.0

[RStephenLegge]

You are a brave man, putting the prop nuts and washers on your deck with those 3/8" openings every 4 inches.  I can't keep up with mine on a table top even.   Good content on this video for running compassmot, thanks

[PauMallol]

Hi guys,

Just another confirmation from my side that connecting APM (2.6 in my case) with power module via USB and powering the quad with the LiPo did not damage the system.

Thanks Randy for your self-explanatory videos! That specific one about the 'compassmot' command really dissipated doubts I had on my GPS+Compass location.

[elbastosrd]

Randy - thanks for your advice earlier. I have just fitted an external magnetometer, compassmot is now 3% - Loiter is now so stable, amazing! Cheers.

[rmackay]

Bntannk,
Power flowing through the battery, motors, escs and power wires creates magnetic interference that throws off the copter. you will likely find on your copter that if you raise your throttle, the heading changes.
This set-up creates a compensation vector that shrinks and grows as you increase the throttle.
I suspect that other systems do not have this compensation but it does work!

[SSBrealty]

Dear Randy.

You did GREAT STEP by STEP VID !!

VID says:
" If the CompassMOT interference MORE than 30%, move away the APM from "

Sorry I cant hear clearly in your VID.

Appreciate your reply. Thanks !

[rmackay]

The easiest thing is to move the APM up a couple of centimeters so that it's further from the power distribution board (or wires). This works for the vast majority of people.
If all else fails you can use an external compass or the GPS+compass that 3dr has just developed.

[rmackay]

Shane,
The next step is to try to tune the declination with ch6. It's likely that you can tune the circling out while the copter is facing a single direction but it's questionable whether you can find a declination that works for all directions. If the CH6 declination tuning fails then the last step is the external compass. I have a flamewheel that I can't get the toiletbowling out of and I'm afraid I will need to resort to an external compass.

[rmackay]

ThinkGreen,
Yes, it will use the throttle position instead. This is less accurate because the relationship between throttle and interference isn't linear. I'd say you should raise your throttle to 50% ~ 75% if doing it this way. Actually that advice holds true even if using the power module.
You can also test using the power module, just make sure the power module is enabled through the mission planner's hardware section and it'll use it.

[rmackay]

Ty,
37% may be ok. Another person I helped yesterday was as high as 60% and his copter flew a-ok. So it's in the grey zone. If your copter isn't flying ok then I hear twisting the power lines together may help. I also hear wrapping stuff in "tin foil" although I wouldn't personally do that. The best solution is going to be to move to an external compass but I think your levels are low enough that you don't need to do that.

[rmackay]

@Pampaflyer, I'm really not sure what trace needs to be cut but I think the trace is used to allow the cpu to communicate with the on-board compass.

[rmackay]

ThinkGreen, nice!
#1. Yes. If you didn't enable the power module before doing compassmot then you'll need to enable the PM and re-do the compassmot procedure.
#2. maybe it's the baud rate? It should be set to 57600 in the mission planner (top right, just right of the com port drop down).

[rmackay]

Voyager,
Try moving the APM up a couple of centimeters so it's further from the power lines. The interference drops off quite quickly if you can move it just a bit further away. If that doesn't help enough then try getting one of the GPS+compass modules. 3DR sells them and I hear some of the clone companies are working on them as well.

[rmackay]

It should be ok to power through the battery and the usb port. I did it during this test and 100 other times I've never had a problem. I highly highly recommend getting a 3dr power module. It makes compassmot work better and avoids a lot of problems people have with power issue.s.

[rmackay]

Excellent. That's in the "grey zone" but I suspect it'll be ok. I think you should try flying it in Loiter and see how it does. If you see "toilet bowling" then you'll need to do more.

[SSBrealty]

Thanks. Randy.

YES. APM sitting close to Power Distribution / Power Wires that cause the Interference !!

With your clear explanation & moved away 1cm, I am enjoying 19% compassMOT now instead of 34% earlier.

_/\_ Thanks you very much !

p/s: TOUGH to find few Centimeters on board :) !

[jimmeeGray]

Randy, putting the gps+compass on a higher pole will work but it requires longer cables...when i called 3DR they told me that they recommend not using a longer cable because the gps+compass module was designed to work with this cable. so it seems we're stuck with this configuration

[BStott]

Hi Randy, After a realization and test ---- Flipping the props accomplishes nothing. Just the rotating the props is sufficient. You affect the same effect.

[JONKYTZ]

Thanks for making this video Randy. My question has to do with using a turnigy ubec and no power module. My used is on the input section with the jumper removed and all ESC power/ground wires removed. When performing the compadsmot should I choose throttle or current. I ask because I'm not clear if current is only for the 3dr pm only. Thanks again for your informative videos.

[rmackay]

300% is tough! You must have some big loops in the wiring. Using an external compass is probably the way to go then. 3DRobotics sells them for a bit under $20 I think. If you're using an APM2.0 or 2.5 you'll need to cut a trace, and I don't know where that is yet but it's certainly do-able.

[grahamhickman]

Hi Thanks for sharing this use full setup..to help holding the quad/hex down have a look here...Compass Mot...