Hi...
I have a Twinstar with two TT .36 PRO.
The engines are running almost perfect, but I can hear that are just a little out of sink.
Is there a way , beside using a tachometer, or steps to follow in order to set up twin engines properly ?
Can someone share their experience ?
Maybe Mr. Robinson master of RC Universe and king of the twin could share some trade secrets ?

Doomking:

With an introduction like that how could I fail to answer? But I dispute the "Master" designators. George Lumpkin, AKA "Twinman," who is also a moderator on this forum is a lot more experienced than I when we're talking about little twins.

But Twinman doesn't worry much about synchronization. He generally sets the planes up so that he can deliberately put the engines out of sync.

I'm the other way. I like to have the engines singing sweetly together.

And there is only one way to lock them together for absolute synchronization without having separate channels for ewach engine and constantly fiddling with the knobs, and that's with a small on-board computer.

The EMS/Jomar Twin Engine Synchronizer costs $90 for the bare box, you have to supply the external connectors and most of the wiring. And wire it yourself. It also has to have metal backplates for the spinners, you mount magnets in them for the rpm sensors. On my C-3/10 the total was about $200, but that included Tru-Turn spinners. Many other less expensixe spinners have the aluminum backplates. But once you have the engines adjusted properly the EMS device locks the engines together. The attached picture is the circuit board. You get it with all the components soldered on, all the wiring yu see has to be added by you. You get the populated board, a box for it, and the parts for the rpm pickup.

Highly recommended, if you want to spend the money and do the installation. It does require separate throttle servos.

Synchro continued in next post.

Bill.

Now the real world.

Use some drill bits to compare throttle settings, play with the linkages - length of the push rods and angle of the servo arms as well as adjusting the position of the levers on the carbs, until you get the throttles themselves matched. Use the drill bits as gauges to check the throttle positions.

Tie the airplane down or use a restraint on it. Now run the engines, each one by itself to begin with. Check the idle mixture as well as high speed. When checking high speed always hold the airplane nose up for at least 30 seconds to be sure the engine doesn''t sag from going lean. Then shut them down, refuel, and start both.

Run the throttles up and down slowly, listening at various speeds. If you can hear a slow beat in the sound you're close enough. Or you could hear an even sound, indicating they're bang on. Or you could hear a fast beat, or at worst hear an obvious difference in speed.

If you have the engines close, with the fast beat, possibly something so simple as switching the props from one engine to the other could put then right on. There are variations in props of the same brand. Or a new glow plug in the slower engine. Possibly both plugs. If you have different plugs in the two engines switch them both for a matched pair.

How do you tell which engine is slower? Easy. Start the engines and peak them, and go that little bit rich you want for flying. Then while they are running at full speed pick either and start richening it. You will hear them getting closer, or further apart. If they are getting farther apart go back to your run setting and richen the other. Play with it, you'll learn how they sound when they are at the same speed.

If it only takes a slight richening of one engine to bring them in at full speed it's safe to use that for sync, but if it takes more than 1/4 turn rich that's too much.

But really, since you seldom run at full throttle, the range from 1/4 to 3/4 is far more important. Put the engines back into their flight tune on the carb, bring the throttle back to 1/2. Listen closely, put your head in front of the plane and you can hear each engine in one ear, and by now you should be able to hear which is running faster. It's time to play with the throttle linkages, that's where you're going to have to work. Adjust the linkage either to raise the speed of the lower, or to slow the faster engine. There's no easy way, and it can take a while. If you can put your fingers on the throttle servos it's a little easier. Turn the radio off and adjust the throttles by hand to bring them into sync, then kill the engines by pinching the fuel lines. Look at the throttles. Since you had the mechanical sync when you began, if you use your drills to measure both openings, you can then turn the radio back on, then reset the throttle links to get the openinge you measured. And this will bring the 1/2 throttle position into sync.

Now restart and recheck the 1/2 throttle sync, if it's good then check idle and full again. You might find you have good sync all the way up and down. More likely the end points will be off. But you will have the important mid range in sync.

If you want to go to the bother you can play with the servo and throttle lever angles and get an excellent match all the way up and down. Yes, you can get the start and end points even, and have one open faster for the first half travel, and have the other catch up in the second half of the travel. This is something for you to play with on a cold winter's evening, just get the mid range for now, and enjoy flying.

Hope I've helped more than I've confused, if there's a question come back and I'll try to explain it better.

Bill.

Thanks for the discussion about the EMS/jomar twin synch module. I've know _of_ it for years, but didn't know anything _about_ it. I'll plan to get one and do some testing with it.

I do like Dan Taylor's suggestion of using an elevon mixer for on-the-fly, by-ear engine synching in http://www.rcuniverse.com/forum/Why_...1131801/tm.htm .
Although the Jomar is sophisticated, the elevon mixer has a certain simple elegance...

--Bill

Who makes/has plans for an elevon mixer that can be used as the engine syncher described above? Can't find find my old one or plans for fabricarting one.

--Bill

Bill:

Using an elevon mixer for the throttles - plug the mixer's elevator input into channel three, the normal throttle channel. Then the mixer'a aileron input will go to channel six. The throttle servos will plug into the mixer in plave of the elevon servos. Then the throttle lever will operate the throttles together, and moving the flap knob off center will raise ont throttle and lower the other.

If you have the right mixes available in the transmitter you can plug one throttle servo into channel three and the other into channel six, not needing to use the external mixer.

Bill.

I can figure _how_ to connect the elevon mixer; I just couldn't remember _where_ to buy the mixer. D:

I just recalled that electrodynamics http://www.electrodynam.com/
has 'em.

--Bill

I had the exact same setup... Twinstar w/ two .36's.

I assume you have a computer radio.
Ch3 for one engine, Ch 7 for the other. Get the throttle linkages close mechanically.
Use the computer radio to "slave" channel 7 to channel 3. Now you start the engines. Use the Ch7 trim knob to trim that engine to the engine on Ch3. Easy, simple and very effective. You can hear when they are in synch by the elimination of the beat note. You can get them nearly perfect this way without any special hardware. I fly a Hitec Eclipse 7 radio.