Metal Parts and Radio Interference- Myth or Reality?

[patmat2350]

From time to time I hear someone warning us not to have metal parts in our models that might have intermittent contact- loose metal u-joints, metal gears, or rod ends for example, lest we lose control of the model due to the resulting radio interference.

I'm tempted to say POPPYCOCK, as I can't begin to imagine that these glancing contacts generate any kind of EMI radiation. Did you ever hear a buzz on your AM radio while surrounded on the freeway by cars and trucks, all of them having sinister metal-on-metal contacts in gearboxes, tie rod ends, and who knows what else? Only time I hear such a noise is when someone uses non-suppression spark plug wires (wire core)… now that's annoying!

Maybe an intermittent connection to ground (water actually) through the prop shaft? Even then I got me doubts.

What say you? Myth or reality? Got any evidence one way or another?

Pat M

[Umi_Ryuzuki]

Gosh, who doesn't have a metal mast, or railings on the the topside of their ship. I see a lot of metal winches on tugs in Seattle.

We have combat ships with aluminum sheathed superstructure. The aluminum sheathing is supposed to stop ball bearings from chewing up the top sides.

It doesn't work, nor does it seem to affect or cause any interferance to the radio systems.

:)

We used to get a buzz on the video cameras when an AM transmitter would cross in front of the camera man.

[patmat2350]

Umi, the alleged concern isn't shielding (which certainly can happen), but metal parts tapping or buzzing against one another, thus causing EMI.

PM

[Kmot]

I have seen it in person. Running a nitro engined airplane. The metal clevis attached to the metal carb lever. Throttle up, and glitching like mad. Replace the metal clevis with a nylon clevis, and glitching is gone. It may be you need massive vibration like a single cylinder IC engine would produce, to get the glitching. Electric motors have no vibration although your drivetrain will have some if something is out of balance or out of round.

[patmat2350]

KMOT- AM or FM radio?

[Kmot]

AM radio on 72 Mhz

[der kapitan]

Hi all,

Some time ago, I built up some small ship models with miniaturized components, and would get some intermittent RF noise, causing the motor to stutter, plus other annoying glitches.

This was traced down to the homemade universal joint between motor and shaft.
It was an all-metal affair made of collets and a piece of brass tubing, held in place by the setscrews. Apparently, that generated enough noise to disrupt the radio signals.

The cure was effected by soldering a wire from the motor case to the stuffing box,
thereby grounding it.

The diagnosis to the problem, as well as how to correct it was made by somebody more knowledgeable about R/C than I.

[fhhuber506771]

RF interference is "strange stuff"

You can get it from metalic paint, metal-metal contact, parallelling the antenna with a stranded steel wire.... The list is almost endless.

Any place 2 different metals come in contact with each other, you WILL produce a sort of battery effect. If the 2 metal objects make intermittant contact, you will produce radio noise. At that point it becomes a question of if the noise produced will be strong enough and cover the "correct" frequency so that you RX will detect it...

Its better to not create an RF issue than to need to track one down... so we try to avoid things likely to cause appreciable interference.

[Shaun Hendricks]

Dissimilar conductive metals can always generate electrical energy, thus RF, when they make contact. The human body, believe it or not, generates RF. A rock, hit by some form of energy (sunlight, etc) can generate RF. None of this is likely to be in massively measureable amounts, however, if it's waveform is sympathetic to the RF signal that is running your RC vehicle, it can add or remove power from the transmission. Wave Theory 101. In AM systems, this is really noticeable and always bad. In FM systems, it's just glitchiness that can affect the vehicle but can also be so mild it doesn't really bother it. I ran a car on AM for a while, moved it to FM and have never looked back. I'm not a fan of AM systems. :D

[Massey]

If the metal to metal contact is well lubricated then the RF noise is greatly reduced that is why we dont get RF noise in our car radios. Just a single tap or a low frequency tap (less than say 30 times a second) will not cause enough noise to really matter to our radio but it will generate RF noise. Now when we have dry bushings in our motors, dry prop shafts, loose bolts (metal bolt and nut) there is enough RF noise to create havok with our systems. Some if not all can be eliminated with proper care and maintenance but some cant. One trick I have learned is to solder a wire from your prop shaft and attach it to the - side of your battery. That will send any stray RF to the ground and put the shaft at the same potential as the rest of the boat. Also some metals when combined will generate more RF or at least RF noise more sympathetic to our radios when mixed. a Brass shaft/brass tube will not generate as much noise as a steel shaft/brass tube. A stainless shaft will generate more than the brass but less then the steel. So metal types play a part in this as well. FM does not get interference as easily as AM but both are prone to glitches if conditions are right.

On the USS Truman we have to ground the latters that lead from the flight deck to the catwalk with a grounding strap. The vibrations of the ship will cause the latters to vibrate and will cuase alot of noise in the ships radar systems and in the aircraft landing computers that are comunicating to the ship as well. Bad situation when the pilots computer tells him the ship is 50 feet away when it is really 100 feet away. At 150 knots 50 or 100 feet mean seconds and that can be trouble.

Massey

[misfitsailor]

I have had this type of interference in both planes and boats, on AM and FM both. A classic case is when metal pushrods cross and can touch each other at some point of travel. Instant jitters! You can prove this to yourself usually by touching some metal part of your boat/plane with a screwdriver or allen wrench when the radio is on. A metal clevis attached to a metal horn or bellcrank can also cause issues. At least it has for me!

[LtDoc]

Something else to think about is that any interference produced by a bi-metal junction needs to have a 'path' to the receiver to cause any problems. If that 'path' is broken then the problem goes away. breaking the path can be done in two ways, either electrically or mechanically. Electrically means capacitors, coils, or grounds. Mechanically means insulating the metal parts from the electrical system in some way (sort of like cutting the wire in an electrical circuit).
Most automotive bi-metal interference is 'contained' by grounding and shielding. If the outer components of an internal combustion engine are metal (and most are), then grounding that 'container' to the rest of the metal car body/frame/etc makes all those bi-metal noise producing thingys sort of disappear from the electical system's sight. The same thing can be done with models, sometimes not quite so easily. Uh, maybe "not quite" isn't exactly the best way of saying it, substitute your favorite 4-letter word for "quite"...
- 'Doc

[johnmca72]

AM radio on 72 Mhz

AM is particularly vulnerable to exactly this kind of RF interference. By its very nature (the 'A' in 'AM' means 'amplitude'), AM signals can be overwhelmed by a stronger signal source. If you've got a dissimilar-metals source of current, & that current is generated repeatedly at regular intervals (such as by rotating a shaft in a bearing, particularly at high RPM), & the frequency or a harmonic of it happens to fall within the range of a nearby AM receiver, then glitches are what you'll get if there's enough energy generated to overwhelm the "good" transmission.

FM is much better at rejecting this type of interference, because it relys on shift between a pair of frequencies rather than amplitude change on one frequency. For a signal to get glitched on FM, your interference source must overwhelm your "good" signal on both frequencies, which is a lot tougher to do (but still not impossible).

JM

[Ghost 2501]

since removing the metal gearbox from yamato, glitches stopped