Gas motor ignition testing/tester..Taking away the mystery!!

[bigrcr]

As many of you know, I am heavily into the gas helicopter model market and flying. I have an ultimate goal as many others do as well, to make the ignition gasoline power plant models as user friendly as they can be.

I have seen, heard of and witnessed many issues in the past years of modeling of the increased "issues" of lockout in the radio systems on gas powered models over those of their glow powered counterparts. This has been the case with airplanes as well as helicopters. The norm for a gasoline powered model airplane has nearly always been to keep all radio equipment out of the motor bay area and not to run a metal push rod back through the firewall of the airframe. The rule of thumb (and motor manufacturer's recommendations) has been to keep all radio gear at least 6" inches away from the motor and it's components. Great...... It's not really possible with the R/C helicopters for obvious reasons. Using carbon and/or metal frames MAY only complicate this issue (being that they are conductive).

As you all know, a notchy bearing, metal contact with vibration, a loose muffler, etc. can cause a nasty situation for most heli models. This problem is even more so using a gasoline powered motor. Many glow model pilots have experienced many loose mufflers, most often without a lock out or loss of control condition. The gas model ,unfortunately, does not share the same fate most often. Why is this???????????

Upon examination and much thought (and obvious reasons), I have figured out at least a small part of this. The main difference is the motor ! Yeh, I know, that obvious! But..WHY????

The gasoline powered motor's ignition system is one that generates it's own power in a general form of AC voltage using a primary coil (that generates a signal/breakage of the current for timing purposes) a secondary coil (that basically amplifies that voltage), a delivery system (the coil wiring and high tension lead) and the spark plug. The motor itself is the reference point of the circuit ( the ground). Gee...... the motor/ignition system is a small AC type power generator, and on board the helicopter!

Remember, for those of you old enough to (or older :mrgreen, granddad's (or mom's for that matter) old car with the AM radio in it? Remember the interference that came through the radio as the motor revved? That was the ignition system noise bleeding into the frame and proximity of the AM radio. These older auto's mostly even used a solid core wire for the coil and spark plugs. Guess what? So do our ignition motors in our models, and they use a solid core wire to deliver the current to the spark plug! Evolution, technology and demand caused the auto industry to start using different wiring for the coils and plugs and SHIELDING! Now you enjoy all of the the wizz-bang gadgets available within your daily commuter vehicle, with no interference.

A few years back, many of the airplane motor manufacturers (Webra, Sachs, etc.) started using a shielded coil wire on their ignition systems. This was to shield the models R/C receiver from being affected by the ignition.

Now, the best solution and a great step forward, is to make the gas model helicopter "think" that it's a glow model. The receiver is working hard to "reject the signature" of the gas motor's ignition system and it does not get much help if the ignition noise is traveling the frames to the components of the radio system. A bad bearing or a muffler coming loose, etc. cannot help and sends the problem "over the top" and overwhealms the receiver. Why cannot we reduce or eliminate the "signature" of the motor so that it is not "seen" by the on board R/C receiver????? That way the model doesn't know it's a gasser!!


How??? In order to get rid of the problem, you have to quantify it and detect the issue. How come some machines can run a full length antenna, most all others must use whips and why does placement of the antenna seem so critical?? Why is this such a mystery??? Why does it seem that making sure there are no issues that will cause you a problem with a perfectly functioning R/C system seems to be trial and error? I have been searching for a magic wand to wave over the machine that could tell me and show me where there is a problem, but there are no magic wands! Or, are there??

In my searches, a friend of mine brought a small device to my attention to try out. He had an issue of lock outs in his graphite framed machine and had gotten tired of searching for the problem. Why the lock outs?? Range checks with the motor not running were excellent. We tried the neat little device on his model and then mine. On his model with the motor running, we ran the device over the machine and viola!!!! The little meter lit up like a Christmas tree! Checking the silicone boot and secondary coil showed no problems, but as we neared the ignition wire (high tension to the plug) the meter would go nuts! The signal from this wire was so strong that moving the meter back nearly 6 inches, still lit it up. What was worse, the meter was run along the frames and radio equipment and the signal showed up there as well.

I then had a good feeling that I had my magic wand. I used the meter on my new Spectra-G, which I had been experiencing a very small area during my motor running (blades off for safety) range testing that I was a little concerned of why at that particular area, my range check was shortened by about 30 feet. This area was always in the very same location while performing a 360 degree around range test. This area was right through the left rear skid area, the motor case and the right front skid,Very odd. This area did put the motor and high tension wire between the transmitter and the receiver/antenna.

I tested the Spectra-G using the meter and the motor running (blades off for safety). The high tension wire lit up like a Christmas tree as well. I waved the device over the entire airframe and found that the signal (noise) was going along the wire, to the vertical ladder piece in the rear and up to the rear channel. The noise was also evident in the throttle push rod. The signal did no however, go to the electrics of the R/C system. This would explain the spot of lessor range through the motor case, but with good range check otherwise.
BTW...... The Stator Gator and it's leads were absolutely CLEAN. I unplugged the Stator Gator and then picked up the signal (noise) from the bare kill wire bullet, but with the Stator Gator plugged in, NOTHING. Thank you MR. Tom Fiddler, you truly did your homework!!!!

I took a length of about 12" inches of household cable TV coax cable and stripped the insulation off of it. I then removed the stainless braided shield out of it. Uh Oh! The braided shield had a mess of gooey/sticky crap on it. Next idea. I then remembered how I clean metal parts for welding (mufflers especially). I filled a small pot with water and Cascade automatic dishwasher detergent and boiled the braided shield in it for 10 minutes. Now the shield is nice and clean with no goo. I then CAREFULLY!!!!!!!!!!! removed the silicone boot off of the high tension wire. This is done by spreading the silicone boot where the wire enters it. Then look inside the boot and you will see the plug connection wire piercing the high tension wire. Take a small screwdriver to lift this wire out of the high tension wire to disengage it and slide the boot and high tension wire apart. The little wire that was piercing the high tension cable should still be intact within the silicone boot.

Slide the coax braid over the high tension wire all the way to the coil and seat it against the plastic case. Take about 1" inch of strands of the shield and twist them into a wire and add a terminal lug. This lug can be crimped, soldered or both (which I did). This method is preferable to me than just adding a small piece of wire under the shield and clamping it all down together. This way, all of the wires in the shield are going to be directly grounded, not just touching a few that are.

Take a small, sturdy tie wrap and secure the shield to the high tension cable right up next to the case of the secondary coil. Pull the shield out tight toward the silicone boot. Carefully spread the boot back open and slide the high tension wire back in and pierce it with the little hook in the wire that is still in the boot. Tie wrap the shield NEAR the silicone boot with the shield stretched. Take care to keep this away from the boot about 1/4 to 3/8 of an inch. Pull the excess shield back down the high tension wire back over the tie wrap and secure it behind the first one near the boot with a second tie wrap. This keeps the frayed ends away from the boot or from getting under it. Use a pair of end cutters and snip off the frayed wires close to the tie wrap and then use some red RTV silicone and insulate from the end of the shield up and onto the silicone boot. Clean the boot first with acetone or alcohol so that the silicone actually sticks.

When putting the secondary coil back on, put the terminal lug of the shield under the bolt nearest the high tension wire where it meets the body and put the bolts back into the motor, reinstalling the coil. Now let the silicone dry. A simple test to see if there is any leakage from under the boot to ground will be to start the motor up and run it in the dark, if you see leakage, fix it.

Now for the test! I fired up the motor of the Spectra-G (again with blades off! for safety). I used the checker and found NO more leakage anywhere!!!!!! Flight testing since this simple modification has shown that there are no more issues. The range that I had lost doing the motor on range test has been restored to normal.

I feel that everyone running a gas model needs one of the simple, inexpensive and readily available testing units. They can be purchased at Lowe's, Home Depot and most electrical supply houses. The checker is:

Greenlee GT-11 AC Voltage Tester About $12.99-$15.00 dependent on where you purchase it. A picture of it and the shield installation is shown in the photos below.

Any of you that have more knowledge of electronics than I do, please chime in with any possible testing devices that may also work or work better! I'm game!

For those of you concerned with the shield going across a frame part and causing RF interference, I believe that it should not matter as long as the frame is also a ground to the motor. Check your frame(s) with an Ohm meter to see if you get near or at zero resistance. Fiberglass electrical tape or heat shrink can be used over the shield if this is a concern.

Hope this helps!!!!!!

[WillJames]

WOW Thanks for sharing that very interesting information!!

You ROCK John!! Thank you!

[Robert Johns]

Wow John!!! Thanks for sharing this info. You da man!!

-robert

[Waller]

I've always spliced in a new cap and shielded cable (the same as used by Desert Aircraft) which has the shielding as well as a resistor cap for added protection.

Now I convert everything to electronic ignition (CH) which has a much better cap and cable, and it shaves almost a pound off the beasty motor...

[bigrcr]

I'm wondering if we can work on Zenoah to add this feature to their heli version motors. The coil wires are way too short as it is, I've seen too many of the coils that the high tension wire is banjo string tight just getting to the plug when mounting the secondary coil in the stock Zenoah location. This is very poor QC on their part.

[Waller]

Originally Posted by bigrcr

I'm wondering if we can work on Zenoah to add this feature to their heli version motors. The coil wires are way too short as it is, I've seen too many of the coils that the high tension wire is banjo string tight just getting to the plug when mounting the secondary coil in the stock Zenoah location. This is very poor QC on their part.

Agreed...

[Billme]

Manoman, I really like this John! This is very significant find my friend. This is going to help alot of folks...Tim, you better treet my man right over there!
Bill

[bigrcr]

Thanks Bill! This is really not a new procedure, the checker is a gem though! I feel we need to implement this type of shielding in our helicopter models, It cannot hurt!!

[cbergen]

John, The Observer is done and test flown with the shielding on it. The customer has an FM reciever for the pan and tilt, and showed zero effects.

I started installing it on my gasser and noticed a few things. When I checked my gasser with the voltage tracer, I was getting hits along the whole length of the wire from the coil to the boot. When I pulled the boot off to install the shielding, I noticed quite a bit of carbon "dust" inside the boot and on the coiled wire inside the boot. I suspect that this is from arcing inside the boot. I cleaned it all up with alcohol and completed installing the shield. Unfortunately, I also found my engine case is cracked from a previous encounter with terra firma , so I won't be able to test it for a few days.

Also, once you remove the boot from the lead as John says, you can then remove the coiled wire from the boot, and when reinstalling, poke the coiled wire into the lead, and slide the boot over the whole shooting match.

I plan on bringing my voltage tracer with me to Sulphur, as well as the necessary shielding and tools to modify anyone's lead who wants it. The whole process takes about 10 minutes tops, except for letting the RTV cure.

This is a handy little tool that John came up with, and did not have to share it with the world as he has done. He could have kept it secret for his sponsors customers, but being the friend and promoter of the hobby that he is, was gracious enough to get it out to all of us.(unlike the engine :twisted: )

Keep up the good work John.

[Billme]

I aggree Chris You better bring a bunch of supplys, because there is going to be a herd of gassers there!

Bill

[FCM]

Great info. John!

Although I have not tried a Greenlee tester (I will be looking to find the equivilent here) I did experience the same directional interference and using trial and error, fixed it the same way as you described. It took days of experimenting to get it all sorted though. Using the tester will be a huge advance over trial and error.

I will be looking for a suitable tester tomorrow for sure

Thanks,

Paul.

[Hacksaw]

Hello, In Mc Master Carr i found "Braided Tinned Copper Mesh Sleeving" with a list of sizes. The 1/4" id is part number 5537K26 at $0.65 per foot and the 3/8" is 5537K14 at $0.76. If you have not used this company yet, you should try them they are a great resource for all kinds of stuff.
www.mcmaster.com

Hope this helps, John

[bigrcr]

Thanks for the info! That's a whole lot easier than stripping out coax shielding. :mrgreen:

[WillJames]

Here is what a DA-150 shielding looks like. Just like my gasser now.

[Festus1567]

Could cure it with this too...

http://www.miniatureaircraftusa.com/...p?prod=125-114

[bigrcr]

Tell me that Miniature Aircraft is not proactive in making things the best!!! :mrgreen:

Later,

[FL350]

I have found this approach to ignition problems here.

[bigrcr]

Great input, Thanks! This is what it takes to progress the hobby.

Later!

[alexander]

I believe MHW had a whole article (5-8 years ago) devoted to gasser high tension shielding (ground loop explained) and grounding using cable TV braided tubing and antenna mounting suggestions with glitch troubleshooting. (I'll dig it out and post later). You'll find the Ergo Z230 came stock with the shielding way back when so it is not a new concept. Funny how it takes 5-10 years for everyone to catch on to what others feel to be standard ignition wiring methods. :wink:

stephen

[Waller]

Originally Posted by alexander

I believe MHW had a whole article (5-8 years ago) devoted to gasser high tension shielding (ground loop explained) and grounding using cable TV braided tubing and antenna mounting suggestions with glitch troubleshooting. (I'll dig it out and post later). You'll find the Ergo Z230 came stock with the shielding way back when so it is not a new concept. Funny how it takes 5-10 years for everyone to catch on to what others feel to be standard ignition wiring methods. :wink:

stephen

:cool: At least people won't laugh at me anymore and tell me I'm anal....

Mine have been wrapped since 1989, when I had lot's of fun with AM receivers and such on my first gasser planks.