I am putting the finishing touches on a SIG Four Star .40 ARF and have finally found something about SIG kits that I am not wild about. I am placing the pushrods for the throttle, elevator and rudder in place. SIG uses a nylon push rod. It is the same type of pushrod I used on my SIG Kadet LT-40 with no problem. The pushrod attaches to the servo arms, rudder, elevator and throttle using nylon clevises which screw into the pushrod. This brings me to my first three questions:

1. Is there a better type of pushrod to use?
2. What is the best type of clevis to use? If the nylon clevis which SIG provides then I want to use it. If not, then I want to go to something else.
3. What is the best type of servo arm to use? I am running Futaba S3004 ball bearing servos.

My final question, may be a little hard to explain. [:-] When I hooked up the throttle control setup I noticed that when the throttle is moved to the fully open position the servo arm (which is rotating forward and toward the center of the comparment) pulls the pushrod away from the fuselage wall and toward the center of the compartment. [:@]Is this bad? [sm=confused.gif] If there a way to stop this from happening?

As always, thank you very much.

I'm always leary about pushrods that come with ARFs. If I were you, I'd use those pushrods for the throttle, as they should hold up fine there. CA the clevices into the nyrods once you get the set to the right length. For the other surfaces, I'd go to a metal pushrod. For the rudder and elevator, I'd use 4-40. NOt because of strength, but because of the length of the run--you don't want the thing flexing like crazy. I'd assume that if it's plumbed for the nyrod pushrods, then the tubes inside of the fuse will easily accomodate a 4-40 rod. Get one that is threaded on one end, and buy a threaded coupler to solder onto the other end. Then, just use metal 4-40 clevises, and you'll be all set. For ailerons, I'd use 2-56 wire.

That's just my opinion.

On the other issue. There are a couple of ways to fix the problem. Number one, you can get a longer control horn, or move the clevise out another hole if possible. This will reduce the amount of swing needed to open your throttle up. However, it might also reduce the "linear" effect that most people want on the throttle channel (unless you can mix that back out with your radio). Another solution (probably the best solution) is to take the control horn off of the servo. Then, move the throttle position to full throttle. After that, replace the horn back onto the servo, in a position that least binds the pushrod, but still fully opens your carb barrel. In order to accomplish this without going to a longer servo horn, you'll need to extend the pushrod--probably by screwing out the clevises on one end, or the other, or both. Ideally, the servo horn should be at around 45 degrees or so on both the full throttle and idle positions. This puts it in as little bind as possible.
I hope that makes sense. I'm a little tired this morning. Someone else can maybe explain better what I'm trying to say.

Good luck.

Michael,

It's been a while since I built my 4* but I think I used 4-40 push rods by sullivan. They slide into the sock pushrod tubs nicely. I'll look them up on Tower's website here shortly for ya.

Clevis' are totally up to you. Personally, I used great planes ez connectors on the servo arm and on the surface control horn I use the nylon variety. Just make sure and use either some fuel tubing or what I use, a small wire tie to secure the clevis on the control horn. Surely don't what it to come apart in flight.

Servo arms, I use the pointed ones vs. the round ones.

On your throttle issue, it sounds like your servo needs to be reversed. Do you have a computer radio?

take care,,,good luck and where is Spring, TX.

These are the control rods I used. They worked and fit perfect into the existing tube. Good luck.

http://www2.towerhobbies.com/cgi-bin...?&I=LXFU99&P=7

Hi Michael,

I vote with cruzomatic on the solid pushrods. I'm just finishing a 4*60 (biy kit) and used those exact rods, I don't like the way the nylon type change trim with temp changes.
My $.02, though on the 4*40 I would go with the solid rods, but use the 2-56 size. 4-40 is a bit on the heavy side for a "40"

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I favor this type of pushrod also. Very little trim change with temperature change using this type of set up.

I do not use nylon clevises on any control surface linkage. I've had too many nylon pins part company from the clevis body to ever trust them again.

Dubro, Sullivan and other name brand metal clevises only. Be careful that the clevis and the threaded wire you are using are a snug fit.

If the throttle pushrod assembly is not binding and causing the servo to buzz, it will be all right even if the outer sheath moves a bit, while providing the action that is needed.

I have a 4* 40 and used the provided Nylon pushrods and I almost always have to trim it out everytime I go flying with it. I have heard you can convert to steel rods but wasn't sure. Thanks for confirming it. The next trip to the hobby shop, I will be buying 4-40 rods to convert it over... Thanks...

I decided to go with the Sullivan metal push rods and clevises. I bought both the 4-40 size and the 2-56 size. The 4-40 seemed a little bulky and was binding in the outer protective tube. The 2-56 seems to work perfectly. Having said that - there is a part in the kit called a "rubber nut." It is just a piece of heavy black tubing about 1/8" O.D., 3/32" I.D. and 1" in length. Does anybody know what this is for?

You cut that into short lengths, and slide it over the metal pushrod. It then acts like a bushing to allow smoother sliding of the pushrod through the outter tube. If you use these (and you should), make sure you locate them where the one closest to the servo, and the one closest to the control surface will not travel out of the outter tube. If they do, they will bind the servo when they try to re-enter the tube. Just put them at least a 1/2 inch from the tube openings on both ends. Hope that made sense.
Then, spread them out evenly--one about every 3 or 4 inches or so. Once in place, hit them with a little thing CA, and they won't go anywhere. Just remember to cut them short enough that you'll have enough.

If I need to explain further, then please ask....
Good luck, and you made a good decision going solid metal!

Have you ever soldered metal pushrods?

The rubber nut may be for the anntenna wire to exit the fuse and flex a bit. I used the standard pushrods that came with my 4*40 with no problems at all. I did insert a piece of wire into the inside of the hollow tubes at the rear end to eliminate any flexing. I get a nice full ele and rudder movement, so much in fact that the plane will snap like crazy with full ele movement at times.

Ernie

I used the Tower Hobbies set up some years ago in a Fun One. I haven't used plastic nyrod centers since then. What a solid set up.

Would a 4-40 bulk rod or music wire be cheaper? I have a 4* 60 build coming up in the future.

Thanks,

Ernie

I am replacing my exsisting nylon rods in my 4* with 4-40 rod as has been mentioned above. I have a question, the 4-40 rods do not move as smoothly in the tubes as the nylon ones did. I am only moving them by hand right now to see how they feel, there is just a little more friction than the nylon ones. They do move ok though with no apparent obstruction though. Is there any kind of lubricate that I should put down the tube or should I just leave it alone and hook them up to the servo as-is? I am not sure if it will be a problem for the servos or not, didn't get that far. Like I said, it isn't that much difference but there is a little more resistance than before with the nylon. Thanks in advance...

Yes, a dry silicone or graphite type lube works good for that. You might even rub some parafin or candle was across the rods if you have neither of the other. Lock Ease works if you have any of that also.

My concern is that those housings are slightly larger than the steel rod, but it might not cause any slop, I hope, I hope.

Good flying my Christian Brother,

Ernie