av8tor1977

My Feedback: (6)

I was ground testing my just finished 50cc Extra and encountered severe servo glitching on all surfaces as soon as I started the engine. Radio: Hitec Aurora 9 with Optima 9 twin antenna receiver with antennas oriented 90 degrees to each other, dual receiver packs and switches running 7.4 volt Lipoly packs through regulators. All high quality Hitec metal geared servos.

So, I started a trouble shooting procedure; first eliminating all switches, regulators, and batteries by plugging a Nicad flight pack directly into the receiver. No change. So then I moved my ignition battery farther from the receiver. No change, but this time I happened to notice when I leaned down in front of the plane with the transmitter in hand, the glitching got much more severe.

Upon close examination, I could see that the RCEXL spark plug cap had not been properly assembled at the factory. One of the little flaps that bends and folds over to hold the cap halves together was folded over, but had missed holding the other half and was trapped between the cap halves. This resulted in a hair line crack in the cap halves being open. Less than the width of an Exacto knife blade. Since I was running a non resistor plug, enough RF interference was escaping through that tiny gap to cause all the problems. I fixed the cap properly, and the problems went away. Just as added insurance, I later also installed a resistor plug, though with a completely shielded system like the RCEXL, one should not be necessary. I was quite surprised that so much interference could escape from such a tiny gap/area in the spark plug cap. Also, so much for 2.4 Ghz being "immune" to interference as some people like to quote!! "Taint so!!"

Somewhere here in the forum the other day, I noticed someone talking about "booster gap" plugs. I highly recommend that these NOT be used for RC. The booster gap can cause a tremendous amount of RF interference. The only advantage in the booster gap design at any rate is it will fire when the plug is somewhat fouled; not needed in our use. If anyone wonders how the booster gap works, just ask and I'll type it up.

AV8TOR

Flathead

My Feedback: (11)

Very interesting, thanks for the information and "THE WARNING" FLATHEAD

ZAGNUT

My Feedback: (1)

no way around it: you really should use a resistor in either the plug or the cap. since the little CM-6 plugs are non-resistor the cap comes with one inside, but the larger caps don't as resistor plugs are available in those sizes.

Nosedragger

Thats odd because the Zenoah EI engines don't have a resistor in the cap.

ZAGNUT

My Feedback: (1)

they use a resistor core cable.

Nosedragger

Then why do they use a shield that is grounded? and shielded cable?

There is no need to ground to the plug base as the ground wire on the ei unit is grounded to the engine already.

ZAGNUT

My Feedback: (1)

a resistor plug is *usually* enough by itself with no other shielding but using a non-resistor plug with a resistor added in before it like is done with the CM-6 isn't the same. i assume it has something to do with the long unshielded path between the resistor and ground as compared to a real resistor plug. since the little zenoah 20 uses the CM-6 it needs the metal cap. i don't know if the larger EI zenoahs use the same plug or the 14mm plugs but they may have also just used the metal caps as added insurance or maybe even found that they had too much RFI and actually needed it. the magneto zenoahs with the little separate coils are also a true CDI system but seem to get by just fine on the resistor plug alone.... having played with them a bit i believe they are putting out a lot less voltage than most of the battery powered CDI ignitions. never measured it but i think it's probably around 10kV instead of the normal 15-20kV