what are they called? and how are they used?
 

the round magnet looking thing people use to eliminate radio interference?
you wrap your wires around it?
my desktop radio had some on the incoming power cable.
what wires do you wrap?

Ferrite rings/beads. You usually only run a turn or two of low-signal wire through them (like the throttle cable of an ESC).

use a small one? and just a loop or two? this is from the esc to receiver wire?

Use whatever size will work - generally just big enough to get the wire through it. Too big and it is clunky and doesn't stay wrapped. One loop is fine, two might shorten the cable too much to reach the receiver. To keep the cable from chafing against the edges, I then use heatshrink over the assembled ferrite ring to keep things in place.

And yes, the "servo" wire from the ESC to the receiver.

I heard somewhere that there also called an 'Eddie current surpression ring' is that true?

AFAIK, eddy currents are basically "turbulence" in a metal core. Supressing them is done by using a laminated core instead of a solid ferrite core; it breaks up the large eddy currents into smaller ones for less "flux resistance". Ever look at the many many layers on a transformer's core?

thank you :great: