EMC Shielding for ArduCopter3.0

Jiro Hattori June 28, 2013 at 10:46pm

Yes, it is really nice.

Here is direct comparison of MagX on a same copter setup.

Randy June 28, 2013 at 10:31pm

Great news. i think I will order some of this and give it a try on my troublesome flamewheel that has terrible compass interference.

Jiro Hattori June 28, 2013 at 10:16pm

I just flew one pack in Loiter with proximate Mu-metal to APM.The Loiter is so stable in XY position and yaw.

The mot graph shows about 10% difference of Mot figure, but almost no uncommanded yaw until lower the battery.

*The copter is worst scenario for AC3.0; Simonk ESC from RC timer, 13 inch carbon propels and 3S Lipo.

Aurelio R. Ramos June 27, 2013 at 1:04pm

So copper tape would help with EMI that might affect the GPS or sonar wiring, but this will actually block static magnetic fields, got it. As far as the earth's magnetic field, while this will have some blocking effect, I based on application it should block far more of the motor's ESC and wiring field than the Earth's. But I think a test is the ultimate way to know.

Keep in mind that an attenuated compass reading is still just as good if the attenuation is not as great as the reduction in interference, because calibration will take care of the rest.

Developer

Randy June 27, 2013 at 12:02pm

Thanks. Maybe you already know but you can see the magnetic field strength in the mission planner's flight data screen's Status tab just below the HUD.

So I'd be really interested to see if there's a change in the magnetic field strength if you:

1. wrap the APM in MuMetal (or equivalent)

2. put a layer of MuMetal below the APM

For these tests I would be most interested in learning the impact on the earth's magnetic field so I think it would be best to test the APM on it's own. So no PDB, battery near. Basically I'm wondering, "as we protect the APM from magnetic interference from the PDB, battery, etc are we losing sensitivity to the earth's magnetic field?".

Also I wonder does it matter the thickness of the material? If you put two layers does it absorb twice as much as a single layer?

I think i may buy some of this and try wrapping the PDB in it. I think a 4-in-1 ESC and battery wrapped in this stuff would have really low interference.

Jiro Hattori June 27, 2013 at 4:44am

My understanding is something like this.

*   Magnetic filed is tend to pass high magnetic permeability material such as Mu metal, Permalloy and Nickel.
    Magnetically high conductance materials are not same as electlically conductive material.
    Aluminum and Copper are good electrically conductive material, but not good for magenetic fileld.
    Most of the caese, those high magnetic coductive marerial tend to be magnet itself.

*   Like attached sketch, magnetic fileld from sources ( PDB, ESC, LiPo) is tend to feed through high Mu material.
    The best scenario is that wrap around those magnetic field sourece by Mu metal.
    Your magnet sensor will not affect from magnetic field from those sources.

*   The issue of utilize those high magnetic field permeability material is that the magnetic field of Earth
     will also reduce near the material. It is something like in the echo free room. (Anechoic chamber)

*   You do not kneed to be grounded for high magnetic permeability material.
    They are act like magnetic field absorber; sponge.

The conclusion:
    1) Put Mu metal near the PDB and ESC
    2) Put magnetic sensor(APM) away from Mu metal

I will test my setup (photo ) that put Mu metal very close to APM (2mm).
The magnetic field from Earth may not enogh for the sensor.
I do not know what is happening.

In Japan, you can purchase from Amazon.

Developer

Randy June 27, 2013 at 3:33am

This is really interesting. The major sources of interference are the pdb, wires going to the ESCs and the batteries. So wrapping them up might help and allow you a more compact copter.

I don't really understand this bit that Hattori-san posted above. What does this mean when it comes to the practical matter of wrapping the offending bits of our copters?

To be effective, the magnetic
shielding must provide a complete path for the magnetic
field lines, in order to prevent the magnetic field.

Developer

John Arne Birkeland June 26, 2013 at 3:16pm

An alternative could be to use coaxial power cables so that you get a perfect "twist" for the entire DC cables. Not sure exactly how much it will help, but should be better then nothing.

Rob_Lefebvre June 26, 2013 at 9:47am

I'm converting my 600 heli to 700 with a direct drive motor on the tail rotor. That means I'll have power wires going through the boom tube. It's rather unfortunate, because with a mechanical drive, the boom is a great place to mount the compass, because it's so far from all the electronics.

I'm thinking about wrapping the wires inside the boom with MuMetal. Hopefully it works out.

Jiro Hattori June 26, 2013 at 12:33am

Thank you for the attention to my testing to utilize Mu metal for magnetic shielding. I agree on every discussion.

I just found the document "Experimental Results with the KVH C-100 Fluxgate Compass in Mobile Robots".

L Ojeda, J Borenstein - Ann Arbor, 2000 - eecs.umich.edu

It said like follows,

To overcome the problem of varying interferences one
can apply magnetic shielding to all major sources of interferences.
There is no known material that blocks magnetic
fields without itself being attracted to the magnet.
However, magnetic fields can be redirected using highpermeability
shielding alloys known as “mu -metal,”
“newmetal,” “moommetal” or “mewmetal.” These materials
are able to divert the magnetic flux to themselves, so
the magnetic fields around them can be reduced significantly.
The deviation produced by the host platform (motors,
wires, etc.) can be reduced with the use of magnetic
shielding made from mu -metal. To be effective, the magnetic
shielding must provide a complete path for the magnetic
field lines, in order to prevent the magnetic field.

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EMC Shielding for ArduCopter3.0

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