EMI Tape?

[Phillip Smith]

I've been lurking a long time and taking a lot of the information on this discussion in.  One thing I keep wondering about is dealing with EMI.  I've seen several mentions of using aluminum or aluminum tape for shielding.  Aluminum is a very poor EMI shield.  Has anyone tried tape like 3M's tin-coated copper tape?  It could be used to wrap ESCs or shield plates in the drone.  For instance: http://solutions.3m.com/wps/portal/3M/en_US/3M-Defense-US/Defense/Products/Air/~/3M-EMI-Embossed-Tin-Plated-Copper-Shielding-Tape-1345-1-in-x-18-yd-25-40-mm-x-16-5-m-9-per-case?N=4294705618+5420242&Nr=AND(hrcy_id%3AGSC0ZTQ2J1gs_0N314XRQJT_N2RL3FHWVK_GPD0K8BC31gv)&rt=d.  I was thinking of picking up a roll and trying it out, but was curious if anyone had already.

Phillip

[Jonathan Challinger]

What specifically are you trying to eliminate? If you're trying to block magnetic fields that affect the compass, it's not likely to help.

On Tue, Jun 11, 2013 at 3:07 PM, Phillip Smith <phillip.an...@gmail.com> wrote:

I've been lurking a long time and taking a lot of the information on this discussion in.  One thing I keep wondering about is dealing with EMI.  I've seen several mentions of using aluminum or aluminum tape for shielding.  Aluminum is a very poor EMI shield.  Has anyone tried tape like 3M's tin-coated copper tape?  It could be used to wrap ESCs or shield plates in the drone.  For instance: http://solutions.3m.com/wps/portal/3M/en_US/3M-Defense-US/Defense/Products/Air/~/3M-EMI-Embossed-Tin-Plated-Copper-Shielding-Tape-1345-1-in-x-18-yd-25-40-mm-x-16-5-m-9-per-case?N=4294705618+5420242&Nr=AND(hrcy_id%3AGSC0ZTQ2J1gs_0N314XRQJT_N2RL3FHWVK_GPD0K8BC31gv)&rt=d.  I was thinking of picking up a roll and trying it out, but was curious if anyone had already.

Phillip

--
You received this message because you are subscribed to the Google Groups "drones-discuss" group.
To unsubscribe from this group and stop receiving emails from it, send an email to drones-discus...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
 
 

[john...@gmail.com]

The ideal solution would be to have a Faraday cage (conductive) enclosure for the entire APM. The only parts that would need to be outside the cage is the GPS antenna.

- JAB

[john...@gmail.com]

I forgot to add. A Faraday cage will not block static or slow moving magnetic fields, meaning that the compass would still work. The effectiviness of blocking EMI from the ESC and motors would depend on the frequency of the noise.

- JAB

[Robert Lefebvre]

I know I would love the option of a nice machined aluminum case. Extra charge of course.

[john...@gmail.com]

+1.

But a simpler quick solution to prevent EMI, could be to try and cover the inside of the APM enclosure with thin metal foil. And of course making sure nothing gets shorted in the process.. :)
GPS would have to be on the outside of course.

- JAB

[Phillip Smith]

3M has an extensive line of EMI/RF shielding products that come in tapes and sheets.  I've been reading up and according to what I read that highly permeable nickel is the best for redirecting magnetic fields.  http://multimedia.3m.com/mws/mediawebserver?mwsId=66666UuZjcFSLXTtnxTynXfEEVuQEcuZgVs6EVs6E666666--

I'm just trying to think outside sticking the compass and GPS up on a potentially crash unfriendly mast.

Phillip

[Robert Lefebvre]

Many things other than the mast have been tried, including MuMetal.  Nothing else works.

[Jonathan Challinger]

It only really needs to be the compass up on the mast. But still, crash-unfriendly.

Then again, why are you crashing? :)

[Cristian Marinescu]

Is that a good product? People said they used it for EMI...also :-)

http://www.homedepot.com/p/Corry-s-15-ft-Slug-and-Snail-Copper-Tape-715/100662157#.UbirLudJM0k

[Craig Elder]

A conductive cage is effective in defending against radiated noise  i.e. electric field but it does virtually nothing to block the magnetic field generated by current flowing to the PDB, ESCs, and motors.

[Olivier ADLER]

According to some basic immunity tests i did i don't think that the APM needs shielding. The board resistance to EMI is certainly strong enough for most situations, except perhaps to travel in space.

And as said previously, a thin EMI shielding does nothing to block DC or low frequency magnetic fields. Even Mu-metal shieldings need to be very thick (and heavy :( ) to be efficient at DC frequencies.

It would be interesting to measure the ESCs EMI spectrum, and see if there is a significant portion of it in the GPS, 2.4 Ghz or 433 900 Mhz bands, but there are chances that they are producing significant harmonics at a few megahertz only.

Someone do have a spectrum analyzer to check this ?


Olivier

[Gary McCray]

Hi All,

There are 2 distinctly different kinds of EMI we are talking about here.

DC EMI which is the primary (problem) for the magnetometer isn't really helped by either Aluminum or Copper and unfortunately any iron based solution acts as a source rather than a solution. (for the magnetometer anyway). And Mu Metal only works if you put the controller in it but leave the magnetometer out of it.

AC EMI, however is damped by aluminum which converts the changing field into heat (nickle also). (Copper does this as well but can also interact to produce it's own electromagnetic field).

Basically an aluminum box around the APM or PX4 would suppress AC EMI quite effectively and you would definitely want your GPS (antenna) to be outside of it.

However, for the unfortunately sensitive magnetometer, you need to reduce its surrounding DC magnetic Field (caused by power supply wiring under power) as much as possible.

For that you need to a. get the magnetometer as far away from the power supply (ESC primary) wiring as much as possible (if possible), reduce the DC power supply wiring as much as possible, twist DC power and ground wires together wherever possible and then apply the correct magnetometer offset to it for your vehicle under power.

Given the huge power consumed by some of the bigger copters (multi and traditional), I think that given the success of the APM and PX4 with no shielding it is relatively safe to say that AC EMI has not been much of an issue as far as board performance has been concerned. (With some exception relating solely to the magnetometer.)

Gary

[Gary McCray]

I should add, I have used aluminum gutter tape around the ESCs and primary ESC wiring to reduced radiated EMI to my SONAR. Works fine with the tape, way to much noise without it.