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

All Day Dan

My Feedback: (5)

Mistake number 1: Always use a spark plug with a resistive element.
Mistake number 2: There is no such thing as a “completely shielded system�.
Mistake number 3: There is no such thing as an RF device that is “immune� from RFI.

You should see the carnage at my field because of actions-assumptions-BS like these. Dan.

dirtybird

My Feedback: (5)

You need to perform more tests to determine that 2.4 was actually interfered with. Remove the servo connections and monitor the servo outputs with an oscilloscope. I see you are in AZ. If you don't have an oscilloscope meet me somewhere and we can use mine.
I strongly suspect the interference was coupled directly into the servo leads and interfered with the drive pulse.
Another way to test it but not as good is to remove the servo from the receiver and drive it from a servo tester. If you still have the problem you will know it is not coming from the receiver. This is not a sure test though because you don't have a full system and the output impedance of the servo tester will be different from the receiver.

w8ye

My Feedback: (16)

CM-6 resistor plug?

av8tor1977

My Feedback: (6)

I only created the post to inform and help others, especially newbies....

AV8TOR

rmh

It was a good post-
a poor connection on the high voltage line/connector is bad news as it spews hash which spreads across all the bands we use

pe reivers

Isn't it a bit academic how it interferes? The end results are jittery or totally locked out servos, even in 2.4 GHz systems. Not doubting you probably are right though. I have been there as well when testing an Old Timer engine with contact breaker and ignition coil. Adding a resistor, RCexl cap and cable shielding cured the condition and we could finally get the 1935 plane to fly. Ignition set to 10° BTDC, 50% oil in the gas mix! ( 1:1). More timing and less oil made the engine freeze.

Truckracer

My Feedback: (19)

One of the most popular plugs in use today, the CM-6 is a non-resistor plug. Just about every new engine uses it and with great success.

av8tor did a good job of noting his observations and resolution of the problem.

earlwb

I had run into some odd problems with one major brand RC system. Everything was fine until I started the engine and then the RX would start resetting it self or something a lot thus rendering the servos inactive.  After trying three RX's, changing the switch harness and battery packs out it still had the problem  So then I tried a different major brand radio system and it worked perfectly fine, no problems at all. I have flown the plane like that many times now.
Go figure.

I have run into the loose spark plug cap causing problems like you experienced too.

dirtybird

My Feedback: (5)

I suppose its academic.
A spark contains nearly all frequencies up to and above visible light.
But in the gigacycle range its very easy to shield out.
I think almost any receiver manufacturer would provide the proper shield or bypass. It doesn't cost that much.
If you look at the gigacycle frequency domain with a spectrum analyzer there really isn't much there other than that due to thermal activity. You really have to be careful with your measurement technique in order to see it.

dirtybird

My Feedback: (5)

In the old 72mhz days if you got an interference signal on the frequency you were using you got an output that you recognized as a glitch.
With spread spectrum you are transmitting on hundreds of frequencies. In order to receive it you need to have a bit in every position at the proper time in order for receiver to recognize it and give you an output. Random noise just wont do it.
This is why the military wanted it. It is extremely resistant to interference and jamming.
You can always transmit enough energy on the band to wipe it out but then you just don't get anything out of it.
I don't see why any loose spark plug will do it. I suspect the interference just went around it to the servo wires.

RonsHangar

I appreciate your comment!!! I used to work for Don Lowe, building, testing engine performance and flying the XBQM-106 Teleplanes or what was referred to back in the day as "mini-RPVs". The initial flight test of this design, using a go-cart engine, met its fate, due to spark ignition RMP - Radio-Magnetic-Pulse. 2.4 was not in use back then. A Kraft Signature Series TX modified for UHF was the ticket. Once the interference was mitigated, the program became a success. See the link that follows below.

Heck I was searching the web the other day, just to see what was out there on the XBQM-106 and this video was found:

http://www.youtube.com/watch?v=6mXjmKDJcBU

I almost fell out of my chair, as I was the one who videotaped the footage of the JATO test flights. A model airlane company in Fairborne, OH had posted it.

Great memories are treasured forever…

All Day Dan

My Feedback: (5)

Great video Ron.
Dirtybird, the spread spectrum band covers eighty frequencies not hundreds. The early Spectrum radios worked on two of them as did the early JR’s. All it took was interference on those two frequencies at the same time and your goose was cooked. Futaba systems work on all eighty. They start at 2,400,000,000 cycles per second. The second one is at 2,410,000,000 cycles per second and up to 2,480,000,000 cycles per second. The electricity in your house runs at 60 cycles per second. Yes, there are radio sources at that high end of the radio spectrum that can interfere with the signal. The JR and Spectrum fliers have learned that the hard way. By sweeping through the entire band of 80 frequencies 500 times a second, the Futaba fliers can have a little more confidence that they will survive any unwanted intrusion from interference. In fact, I do believe that JR and Spectrum have switched to that type of frequency hopping a while ago. But that does not mean we can let our guard down. As one of the posters pointed out, the arc of the spark plug can contain frequency components from DC, the voltage coming out of a battery, to light and that includes the 2.4 frequency range we are flying on. So, don’t defy the laws of physics or don’t f with Mother Nature, live with them. Dan.

coronabob

My Feedback: (10)

You brought up some good points that I would have nodded my head in agreement. We had an interesting event at our club. I had a Brison 2.4 ci with a CH ignition (alum box) but a rubber insulated hv cable going to the plug. The drain wire in the cable is bolted to the engine. I flew that engine quite a few times in different planes w/o issues on 72MHz PCM. I sold the engine on consignment and it went thru a couple of owners and ended up in a friend's hand.

He had it installed in a proven airframe and had trouble with severe glitches. He asked me to help and I recognized my old engine. He has a Futaba 2.4Ghz in the plane. He followed different advices and I tried to look for obvious metal rubbing sources, etc. I was looking for conducted noise and kind of suspected radiated noise getting thru the wiring. None of the fixes worked. One day I called and told him to wrap his hv cable in alum foil and over wrap the foil with just duct tape to keep the foil together. That fixed the glitching, period!

The rubber insulated hv cable w/o the jacketed braid shield was the culprit. I must say that it did work for me. I suspected that maybe the drain wire was busted somewhere under the insulation.

dirtybird

My Feedback: (5)

The number 80 is the number bands not frequencies. There are are 80 bands that each contain 1,000,000 frequencies. In that band the transmitter sends out hundreds of frequencies that much be detected and matched to the code the receiver has.
If you wiped out two of the bands your goose would surly be cooked.

Four Stroker

You guys are all wet. There are no pre-defined frequencies in the 2.4 GHz ISM band. You can divide it up any way you want. This 80 channel misconception was initiated by Spektrum some 7 years ago. They used 80 channels. WiFi uses 12 overlapping "channels". You can download FCC part 15 section 247 and read it for yourselves.

raptor30se

This is a good heads up, I lost a 30cc due to this exact thing. I have a new DLE 35 with newer 120 ignition cap that doesn't fit as tightly as the older 90 degree caps, it was arcing under cap causing interference that was bad, radiating from the ignition battery and all around the engine. I am flying Futaba FASST and it takes alot to make it jitter but it will. I tested again with an older DMS2 spectrum receiver and can knock it out instantly when engine running. I bought a ignition tester, basically unplug hall affect sensor and plug in this function generator to drive the spark without needing to run engine. This has been great to prove the theory and see what happens. I work in IT so have access to 2.4 spectrum analyzer. When the arcing is occuring it blankets the entire sprectrum with noise across the board.

radfordc

My Feedback: (14)

All the ignition systems I have used have a resistor installed in the lead going to the spark plug. Serves the same purpose as a resistor plug.

dirtybird

My Feedback: (5)

Your right. I just got out of the shower so I am all wet.
And about 80 channels you are correct it is not a standard.
On 2.4 you can divide it any way you like. Its 80 mhz and Spectrum chose to make each of its band 1 mhz.
I am not sure what Futaba uses but 1 mhz seems a logical choice.
BTW Spectrum chooses 2 bands but that is for spatial diversity, not interference rejection. Futaba and other band hopping systems use all bands so they theoretically don't need it.

dirtybird

My Feedback: (5)

This is not a fair test either. When an engine is running the spark plug is inside a metal cavity which is a great shield. Rf escapes on the coil connection but it is greatly attenuated. Try it with the spark plug in the engine and your loose spark lead. You wont see much on the spectrum analyzer unless your connection is so loose the arc occurs outside of the spark plug. In that case the engine wont run.
If there is an arc outside of the engine and you are close all bands will be wiped out and none of your receivers will work. Not even Futaba.
If you say Futaba works and Spectrum don't ,I will be damn suspicious of your testing methods.
There are thousands of ways of making testing mistakes. I have been in the electronic testing business for 50 years and I have made them all.

raptor30se

I understand, the plug was in the engine during this test. I will do a video and post to youtube later this week for you to see the difference. The Spekrum receiver I had is a knock off HK orange DSM2 as I don't fly specktrum so it maybe more suspectible than OEM receivers.

dirtybird

My Feedback: (5)

Posting on utube does not change the results.
I don't disagree with what you saw. I just disagree with your analysis.
If it were my A/C I wold be looking for some other cause because it may bite me later.

Four Stroker

Most companies jump by 1 MHz (1.023 MHz) because the chip they use does that. Chips are about $1. Making your own chip about $6M fixed cost.

I am with DirtyBird, servos don't dance all around on 2.4 systems. At least not from interference going into the antennas. Even if they miss all of the packets, the servos just sit there. Now maybe he meant they were jerky while he was moving the sticks around about.

raydar

This is a picture of my HT lead chaffing on my cowl on a 55cc sukhoi, the engine missfired for a while then deadsticked before I had a chance to land. No damage done.

The model has a futaba fasst 2.4 reciever and shares one a123/life battery with the ignition through a opto kill. Zero interference was experienced.

mikes68charger

My Feedback: (34)

Wow,

I pulled my ESM Corsair out of the storage to get ready for this years flying, as she flew great last year.

Pulled her off the wall, and turn it on, and every thing was ok, then I gave up elvator and rudder at the same time, and all my servos were freaking out. Elevator went from full up to full down all on its own etc.

I moved every servo and it kept happing.

I pluged a 5cell nicad right into the reciver with no change.

I rebound it, no change, and the plane was not even running (DLE 55RA)

I started to pull servos out, (all Hitec 645) but once I pulled out the Hitec 85 for the retract swich all was good in the world.

It was odd as the retract servo moved like it was supposed to, there was no nose (stran ) on the servo.

I replaced the servo and have not flown it yet but on the ground all seems to be fine now.

Was this a interference issue?