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[malcolmfrary]

In a recent post, it was noted that RF interference was caused by metal to metal gears.  Now I wonder about this.  While it is quite possible that twirling lumps of metal can cause electromagnetic fields to be created at a level to upset radios and other sensitive electronic signalling devices, what is it about gears that actually causes the problem?
Is it something that only happens with an electric motor involved?  Or does the problem and cure happen with I/C, live steam or elastic band power?  Given that plastic gears are unlikely to create interference, does it matter what actual metals are involved?  Is it friction between metal gears doing something that has passed mainstream physics by on its way?


Questions courtesy of too much homebrewed Ouzu.  I do acknowledge that strapping everything both visible and imagined to the ground line of the power supply, and preferably to the water that the boat is floating in, helps, but I am left wondering, "Why?".

[dreadnought72]

It's friction that causes the charge build-up on Van de Graaf generators, so no mainstream physics is being hurt in that process. And sharp points make for good charge-leakage. So maybe metal-toothed gears are positively good for interference? 

...Well that's my "only one cup of tea this morning" suggestion, and I'll stick to it until someone more knowledgable comes along...

Andy

[malcolmfrary]

True, but a VdG generator usually involves friction and insulating material to generate static, and the basic idea of metal gears is that they are constantly in contact with each other, even if it is a moving contact. 

[NFMike]

I suspect the interference with the MFAs is just the usual brush/commutator stuff. I find it hard to believe metal gears not insulated from each other will build enough charge to cause the arcing needed for significant interference.

[john44]

Hi guys,
I was told by a radio tech.A long time ago, that the reason for interference is
because metals are always covered by an oxide film,due to metal reacting chemically
with the oxygen in the air and that metal oxides are semiconductors,
so when 2 coated(mating) parts are in movement it causes RF currents to
flow which could cause significant levels of interference to Reciever.
So with a gearbox running quite fast that is a logical reason.

If it is the same post I placed a reply in, I know it was the cause because
I re- routed the wire. Ran the motor, no glitching, placed the wire back where it was
just to prove my point, glitching, and the motor was suppressed.
re-routed the servo wire away from the gearbox cover, no glitching.

If I am wrong someone will correct me, but it works for me.

john

[NFMike]

Well it's plausible (I'll have to poke around a bit) but in this case I'd think that moving the wire near or far from the gearbox is also moving it to or away from the motor and casing. The suppression does just that, it doesn't remove the interference completely, so physical separation is needed as well.

[NFMike]

Thinking a bit more, if there are stray magnetic fields from the motor magnets then the gears moving in those could generate some voltages.

Still a bit doubtful as any significant electrical activity in the gear train would lead to pitting and rapid wear.

[Netleyned]

If the motor is run without the gearbox the answer should be apparent.
Gearboxes also have some sort of lubrication between the contact surfaces.


Ned

[unbuiltnautilus]

If you run a metal screwdriver along rudder pushrods you will very often induce glitching, metal to metal. Using the same logic an IC engine, all metal, should cause all manner of trouble when running, it doesn't....discuss