guys,

One of my original beta testers wrote up a "how to" on range testing as well as covering a number of nuainces with the walbro carb. Thought that I would share it with everyone. A lot of good info (a nice plane too - pics attached):


TWIN SYNC


INSTALLATION REQUIRMENTS FOR ZENOAH ENGINES


by RICK SIMMONS 2engsout


First of all, it is imposible to fully shield the RF field of a magneto equipped engine, BUT, the procedures below provided me with a full throttle-both engines, antenna colapsed range check of 275' with my G-45's, and 215' with my G-26's with the twin sync installed. I use a JR 8103 TX with the PCM 649 RX and the Revolution 6" loaded RX anntena pt # Revo 1010 from Horizon Hobby mounted below the fuse.

1. On all of my Zenoah engines, I use a Bosch spark plug resistor cap and the high tension lead " sheilding " that C&H Ignition sells. The caps are $15.95 each. C&H ign. phone # is 307-857-6897. You will also need resistor spark plugs if you don't already have them. Tell them what engines you are equipping. The G-26's also require a C&H resistor cap adapter for the smaller 10mm plug. They sell for $2.00. The shielding needs to be grounded at BOTH ends. Simply scratch some of the nickle plating off the Bosch cap where you want to solder the shielding to it. ( I used a small Dremel grindstone to remove the plating). On the other end, twist some excess shielding into a roll and solder an eyelet on the end, and then ground it to the engine case. It takes some heat to warm the cap up to get the solder to stick, so be prepared. My throttle servos jittered when the engines were running BEFORE I shielded the plugs and high tension lead. That jitter is RF interference getting into the hall sensor leads sending spurious signals to the twin sync unit, which then return spurious signals back to the throttle servos.


2. On the G-26's, you will mount 2 magnets in the spinner backplate. You CANNOT mount the hall sensors using any type of metal or conductive material ( also no carbon fiber). I used 1/8" thick plastic "L" shaped brackets to mount my G-26 hall sensors. The short end of the "L" was drilled 4mm and bolted to the front of the engine using one of the engine case bosses. There are 4 bosses to chose from. You may also use plywood mounts. The hall sensors can be mounted behind the engine on the G-38's, G-45's and G-62's utilizing the rear crankshaft exstention. This was done on my Ziroli DC-3 (G-45's) because I have a scale 3 bladed prop with a dummy engine and wanted to retain a scale propeller appearance without having to mount a spinner backplate behind the prop. A plastic disc, or any spinner backplate can be used. It is mounted to the crankshaft by using a 8mm x 1mm nut. On my G-45's, pictured below, I use spring starters, so I took a 10mm socket and removed the 8mm x 1mm threaded nut holding the spring starter sprage in place and used a 1/4" coupling nut, which is simply a nut that is 3/4" long with a 1/4" thread inside of it. I took it to my machinist and he put it in his lathe, drilled the inside dia. at .275" 3/4 of the lenth of the nut. Then he ran a 8mm x1mm bottom tap into that .275 hole, while it was still in the lathe. DO NOT try to "free hand" drill and tap this without using a lathe because it has to be perfectly aligned on axis !! If its not perfect, your disc will wobble !! This nut replaces the nut you previously removed from the back of the spring starter. Use red locktight to install it and just snug it up. DO NOT OVERTIGHTEN. I used a 3.5" dia. nylon spinner backplates to hold the magnets. I carefully scribed a line across the backplate directly thru the center hole. I measured in 3/8" from the edges and drilled my 3/16" holes to hold the magnets. Be sure to center punch the hole location on the scribe line , and then drill a 1/16th pilot hole, then a 1/8th hole, then 3/16". Before you epoxy the magnets in place, plug a hall sensor into the twin sync unit, power it up, and run the magnet across the face of the hall sensor. You only want one magnet to activate the hall sensor. If the green LED dose not light, then flip the magnet around and try the other side. Mark the side that lights up the LED and that will be the side that faces the magnet. Do this now to all 4 magnets and then go ahead and epoxy them in place. I then use the lathe to drill the hole in the backplate 8mm. Use 2 flat washers and a lock washer to hold the bakplate to the coupler nut. Use a flat washer on BOTH sides of the backplate. Use blue locktight on this bolt and DO NOT overtighten. Just snug. It will begin to slightly crush the 6mm plastic crankshaft insert, which is OK. When completed, check for runout. Now mount your hall sensor with a 1/16" air gap, using a wood mounting bracket if you can and check that the green LED lights up on the twin sync unit. Run your hall sensor leads thru your wing and to the twin sync unit keeping the leads as short as possible and not in the same wiring loom as the aleron, flap and throttle servo leads, if possible. IF you do not have spring starters on your engines, simply drill a 8mm hole in the backplate and using 2 flat washers, sandwich the plate and retain it with a lockwasher and 8mm X 1mm nut using blue loctite. The G-45,and G-62 crankshaft threads are 8mm x 1mm where the spring starter attaches. It is possible to install the disc behind the G-38, BUT the crank exstention threads are LEFT-HAND, 8mm x 1mm. This takes a left hand tap of corse, and the nut cannot touch the back of the spring starter sprage, due to the different way the starter is installed. If you would like a detailed G-38 disc installation supplement, email me and I will send it to you. This completes the magnet and hall sensor installation.






RANGE CHECK PROCEDURE


I use a systematic range check procedure that you may find helpful.
The aircraft must be securly anchored and pointed in a safe direction to preform these range checks.


1.This procedure pertains to PCM use, but can still be adapted for FM use also. For FM operation, the chip has a fail-safe capability programed into the twin sync unit that will pull your throttles back to idle if there is a loss of TX signal. When you are ready for a range check, use a standard "Y" connector to the engine throttle servos plugged into the throttle ch on the RX for a baseline distance check without the twin sync plugged into the system. I had to run the hall sensor leads and the throttle servo leads between the wing and the fuse when assembled so that I could get to the unit and the leads for easy access while range testing. Be sure to use a foam cushion in the wing saddle area where the wires exit to protect the finish. Mark this baseline range distance by placing a marker on the ground at the point where your throttles STAY at your PCM failsafe preset posistion ( hi idle ). The 1st check will be with engines OFF, with the TX stick at FULL throttle. Have a helper watch the throttle arms on your carbs and have him raise his hand whenever the throttles go to idle ( preset failsafe posistion). You will notice as you walk the TX farther away from the plane, the signal will drift in and out somewhat. I eventually found the distance that I could move the TX 4' farther back and the RX would go into fail-safe and not drift back. Mine JR TX was that sensitive. Take your time. I would then drop my baseline marker at that point.


2. Now that you have marked that baseline, step off and count your paces back to the plane and write it down for future reference. Then start each engine and tweak the needles accordingly to get your best response. Both engines will be running at full throttle on the ground for several minutes, so go a little richer on the top end adjustment for added cooling if neccesary.
Repeat test #1 and mark your distance to fail-safe (hi idle).


3. Now we know EXACTLY what the RF, if anything is doing to the reception between the TX and the RX, WITHOUT, the twin sync installed in the system. This is your baseline range. Now remove the "Y" connector, and plug in the leads to the correct "J" pegs on the twin sync unit. REMEMBER , the negitive wire goes towards the edge of the board !! Now, with both engines OFF, start walkin, antenna colapsed, and the TX stick at full throttle. Keep working the fail-safe point till you can find the 4' area that you "have it" and "I dont have it". Mark that spot and compare the ranges. Now start both engines and at full throttle, repeat the test. I can't tell you what range is going to be 100% safe for you, but I got 215' with my G-26's and 275' with my G-45's and had no PCM fail-safe occurances in flight. Use your best judgement.



TUNING THE WALBRO CARBURETOR


In order to give the twin sync the best possible chance to respond to 2% changes in the servo output, you will need to observe the throttle output % on your throttle curve. You MUST have atleast a 25 RPM increase with each 2% increase in throttle output. If you do not, you may have a flat spot (LEAN SPOT) in you mixure adjustment at that point. This MUST be corrected !! Note the % output of the flat spot for future reference when you go to the tuning proceedure. Usually the flat spot occurs right above idle, or at approx 1/2 throttle. Richening the low speed needle is the 1st cure, BUT you will need a reliable and smooth transision to the upper rpm ranges also. If you find that your Walbro carb has a nice idle, but seems to smooth out and go flat (LEAN) at 1/2 to 5/8th throttle, with little increase in rpm by moving the stick in the midrange, you probably have a pop-off pressure set too high. Since your high speed needle is set just right, and your idle is set just right, you have no needle to tweek for the midrange mixure adjustment !! BUT, you have a pop-off pressure adjustment that can lean or richen the midrange. This is done by adjusting the stiffness of the spring thats under the metering lever, above the needle and seat assembly. To richen the midrange by changing the popoff pressure, you 1st need a baseline reading of your pop-off pressure. EC Distributing (www.eccarburetors.com ) sells a 0-30 lbs. gauge that will tell you exactly what your current pop-off pressure is. It sells for about $33.00. Simply connect the hose from the gauge to the fuel inlet nipple and start pumping up the pressure. Its more accurate if you can dribble a little gas in the nipple to make sure the carb is "wet". I have found that many Walbro carbs have factory popoffs that exceed 30 lbs. Once your have your baseline pop-off, you can start trimming the spring lenth by clipping off 1 coil at a time using a toenail clipper. This softer spring will now allow the hi speed circuit to "come into play" a little sooner then it did before, and richen your midrange response. Recheck your pop-off pressure before starting your engine and note the change. You may now be able to slightly lean the low speed needle to smooth out the idle a little. All Zenoah engines have a fixed ignition timing at 28 degrees before top dead center, and that makes for a lumpy idle. Keep checking your response just above idle and at the throttle output % that had preveiously been flat. You may have to repeat this spring trimming proceedure several times to get it perfect. You can also get extra springs of different stiffness and spring shims to fine tune the popoff pressures from EC Distributing. I have found that the engines best response has been with a popoff pressure between 20-28 lbs, depending on engine displacment. Each .010 shim raises the popoff pressure about 1/2 lb.
When you have a popoff between 20 - 28 lbs. start your engine and see the difference. You may have to now lean the low speed needle slightly to smooth out your idle. Check throttle response and adjust accordingly. I set my high speed needle for peak RPM, then go 1/16 turn richer to compensate for the prop unloading in the air and the engine turning 500 RPMS higher. This is critical because the carb will not let any more fuel thru just because the engine is now turning faster in the air. The 1/16th turn richer than peak RPMS now covers this increased fuel demand.



Take the time to get it perfect !! Your plane deserves it !!


Rick Simmons 2engsout [email protected]



G-45 sensor mount5.jpg