Trying to finish a Kangke extra 300. It came with V shape push rod for the elevator but it binds all over the place. I have tried different push rod sizes 2'56 and 4/40 to no avail. I am thinking of adding two servos to the back side of the fuse,is there a technique or best place to put the, my first time. Thank

The installation is easy. Most are under the leading edge of the stab. Most planes have enough wood in this area to mount the servos. Driving them is the biggest problem guys run into. If your radio won't drive the two servos you will need a reverse "Y" harness. Things to watch for....Lay the servos on the bottom of the fuse and make sure they don't hit on the bottom. If they do ,you can stagger them or shim them out with a little ply. You need a little ply for the screws to go into anyway. If you have the room the ply can go inside the fuse. If not use it as a spacer. Make sure you have some wood around the mount area. These servos need to be surrounded on 4 sides. Another problem could be in the CG of the plane. If the plane is designed for a forward mounted servo, you can adversely effect the CG. To get around this, you can use micro servos, and/or slide the engine out on the mounts as far as possible. It is also possible to mount two micro servos in the stock location and run a sepperate push rod for each one to the tail. This is actually easier if you have the room in the fuse. Plus a stock "Y" harness will drive both servos.
I would post you a few pics of both ways but I am at work. I can add them this evening if you want. Let me know.

David

Yes David I would really appreciate it. My biggest concer with this plane is the push rod for the rudder. The exit is below the exit for the elevator push rod. I am not concerned about the CG lead can alway fix that and also move the battery all the way forward. How far away from the control horns should the servos be mounted? I was think to make the rod about 6 to 7 inches long, using 440's. I have a couple of Y connectors so that is ok. Thanks for your response.

Richard, I regular Y harness will not work with the servos in the tail. You need some way to reverse one of them. I suppose you could mount one servo above the push rod center line and one below if you have the room. Most are done level to each other and one has to be reversed. I fly with a Futaba 9C and it will do it. It all depends on the radio.
The length to the elev halves is not critical. Most are mounted in the area under the stab for two reasons. One is ,there is normally some strength in this area for the mounts. Two is, it hides the servo from view when looking down at the airframe.

pics in next post, David

Ok, so here are a few pics. Sorry for the quality, my camera is having problems.
Notice the pull/pull is under the servos. You could run your rudder pushrod in this area. Also notice I used micro servos. I did this because I had a pair. Standard servos would have worked. One thing you can't see is after I cut the opening for the servos. I joined the two sides of the fuse with a 1/4" square balsa stick right behind the servos. Even though this plane has ply fuse sides, I wanted to be sure there was no flex in this area. I fly my stuff HARD. So a litle strength pays off in the long run.

David

I'll just add some pics of how I did my Extra. I use a 9C, but I have used reversing Y's in the past with no problem. One half lags slightly, but it's not noticeable unless you jam the sticks.

Thank for the pics. I use a Futaba 2.4 7C not sure if it will do it. I assume I can place the servo backwards or something like that. Will have to play with it. Gotta tell you I find ARFs more complicated than stick buidling. Thanks for the help.

Richard, turning the servo backwards makes no difference. I think the new 7C does have this ability. If you can't find it in the book, ask over in the radio forum. Someone can help you.

David

Dave's right. You'd have to flip the arm so one is up and one is down. This would really screw up the linkages, and the halves would never be right with eachother.

Thanks guys

Yes the 7C does have the ability. However you will experience the lag between the 2 servos. I opted to use a Futaba servo sychronizer/ Jr Match box / Smart fly Equalizer for perfect match.

I'm not quite sure where the lag comes in when using the radio and separate channels. Mine doesn't do it and I'm running two Hitec HS-7985MG's on my elevators. They both move at the exact same rate up or down. (real fast I might add)

P.S. I know Dave is referring to lag when using the reversing Y cable but I don't believe there is any lag when using two separate channels in the radio for this function.

Here's an old old thread that's got a few posts of one of my Edge540's that I installed rear-mounted servos... if you look at the thread.. just scroll down about half-way to my pics/text... it lays it out decently.
As for the one servo needing to be reversed... I got a "servo-reversing Y-harnes" It was $9.00 at Horizon... these have a potentiometer so you can match throws exact..servo to servo.
The date on the thread is Nov.'02... the plane, servos, all of it are still going strong..matter of fact I'm flying it again this weekend. Check it out.. this does work well, and is easy and affordable.

http://www.rcuniverse.com/forum/tm.asp?m=359864

Not to discount what dgrant said. But I have owned three of the reverse Y's and one of them worked right. The other two would change trim in flight. Kind of a pain to land a plane when one elev half is tilted 10 degrees. Maybe mine were out of a bad batch, many guys have great luck with them. However if your radio will mix it in, that is the best way to do it. If the mix is set up correctly there should not be a delay. On the 9C I use channel 5 and have it on 6 planes that way. Never an issue.

David

Got the servos and measured them againts the tail where they should go but they are too large and would not fit. The other solution is what Dave did and use micro. It will have an OS 75 Ax on it and not sure if micro servos are strong enough? Thanks

There is a OS 1.20AX on the nose of the ULT in my pics. The micros are 40 some oz each. That's 80oz of torque. Your 62" Extra should not be a problem. Just be sure you buy the right servo. Go metal gear for piece of mind if you need to.

david