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I have a robot with a lot of servos in close proximity and a high-current DC motor powering an airsoft gun. The motor is causing electromagnetic interference with the servos, and we need to shield it somehow. The problem is, we're at a competition, so we need something that can maybe be bought at a convenience store.

Can aluminum foil be used for EMF shielding, and if so, would more layers be better or worse? What else could we try to use?

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    \$\begingroup\$ I think you mean "EMI" as per your earlier question: electronics.stackexchange.com/questions/162125/… \$\endgroup\$
    – Andy aka
    Mar 28, 2015 at 15:50
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    \$\begingroup\$ You have to work out what you are shielding against. Your previous question had feedback that basically asked you for more detail and you should really try to do this in order to get a decent answer. Aluminium foil won't protect agaisnt magnetic induction - try some mild steel plate or put ferrites on the ofending wires. How about a picture of your thing to give some idea of where the problem may lie. \$\endgroup\$
    – Andy aka
    Mar 28, 2015 at 15:54
  • \$\begingroup\$ Copper tape is neat. Dunno if you can get it at a brick and mortar store, though. It just shows up at my work. (Shout out to the lab maintainer!) \$\endgroup\$
    – dext0rb
    Mar 28, 2015 at 21:21

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To answer this question, yes, aluminum foil can be used as shielding. After all, many shielded cables use aluminum foil or aluminized mylar for exactly that purpose. However, aluminum oxidizes rather readily and its oxide is an insulator, so it can be difficult to maintain a good electrical connection to it. Screws with lockwashers can be effective.

However, in the comments on your previous question, we've pretty much ruled out EMI as the source of your problem anyway. You need to go back to that question if you want a quick solution.

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My prediction is that it's highly unlikely that you are getting EMI from your motor as interference. Motors generate a lot of electrical noise, and if that noise gets passed into your servos power rails, you'll get unexpected behavior.

Try adding capacitors to your motor in this fashion: + lead to - lead, + lead to motor case, and - lead to motor case. Use a value of 10ish pF. This is a commonly used method to suppress motor noise.

EDIT: Don't forget to add filtering capacitors to your servo power lines! A 47uF cap between power and ground can do wonders.

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  • \$\begingroup\$ 47µF, rated for twice the operating voltage, and of a type in this order: X7R ceramic, tantalum, low-ESR hybrids, then electrolytic. Reason being, standard electrolytics have the highest ESR, so will do the least to filter out noise. NP0 ceramic would likely be the best, but 47µF would require a lot of physical volume and be cost-prohibitive. \$\endgroup\$
    – rdtsc
    May 12, 2016 at 15:48

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