Please help out a newbie...this is the first time I'm putting together an ARF (or pull pull or any RC related stuff for that matter). I've read a bunch of posts on here about pull pull systems but they are beyond me and don't answer some basic questions I have. This is for a 3D Mayhem with a OS .91 2 stroke engine and 5625mg Hitechs. Here they are:

- how do I accurately figure out the exit holes of the cables
- how low/high do I place the control horns on the rudder (i know about the hinge line and ackerman)
- does the cable need to be parallel to the fuse or can it go from the servo arm to the bottom of the rudder
- does the servo have to go with the output arm closer to the rudder
- will the stock arm do (2" arm, seems very solid)
- what holes do I need to put the cables in (at the servo and at the horn)
- how do I test the tension of the cables inside the fuse once they are all installed?

I know these are a bunch of questions. Thx in advance

Strulag,
#1 Once you have a idea were you want to mount the servo I use a small laser light . I place it at the location of the servo arm and shine it back into the fuse to locate the strightest line to the rudder control horns. Don't be scared to cross the cables if it will make the line from servo to rudder horn strighter.
#2 I like the cable to be at a 90% angle to the ruder hinge line
#3 same as #2 you have to find a compermise in the servo location and the control horns on the rudder but try to keep the cable at a 90% angle to the ruder hinge line
#4 I mount the servo output arm eather way but make my decision based on the wires leaving the servo in the best line to make it to the RX, also make sure your servo arms miss things when at a extreem angle.
#5 stock arm will do unless you go to the larger planes
#6 what holes do I need to put the cables in (at the servo and at the horn) Just make sure the cables are the same with apart at the servo & rudder horn.
#7 how do I test the tension of the cables inside the fuse once they are all installed. they should be to were the slack is out but not to were ther is actual tension on them.

If you don't understand something I wrote feel free to ask.
Roy
www.H.P.Pilots.com

#2 - what do you do if you don't have a laser?
#6 - keeping it at the same length do you put them more towards the outside for more control throw or towards the inside. or in the case of pull pull it doesn't really matter

#2 - what do you do if you don't have a laser? Use a long pice of music wire or you will have to just eye ball it
#6 - keeping it at the same length do you put them more towards the outside for more control throw or towards the inside. or in the case of pull pull it doesn't really matter It woun't give you more throw but keep it to the outside
Roy

Mount the servo and the rudder control horn. Mark the servo arm height on the side of the fuse. Stretch the cable between that mark and the rudder control horn, mark where the cable touches the fuse near the tail. Do the same thing from the bottom. Mark where the servo arm is on the bottom, stretch the cable between the two points and mark where it intersects with the line marked on the side of the plane. Pop a hole in the side and fish a cable in there to check how it lines up. Then make the hole into a bigger slot when you know where exactly where the cable will move around. Normally the control horn goes towards the bottom of the rudder just because that's a convenient place. I attached a pic of one I made outside the fuse. You could do that also on the bottom of the plane. A also attached some of my CAP232 120. I crossed the CAP232 cables. One cable is slightly slack when at full deflections but it does not cause any problems after many flights. Also my cable goes through some antenna tubing that I CA'd to the side of the fuse. This keeps the cable from rubbing on the wood. Some people will say to not have it touch anything as it goes through the fuse but it doesn't cause any problems at all.

I finally got my pull-pull installed. I put the rudder horns a little behind the hinge line to prevent the cables from getting tight when the rudder is deflected. Well....it's now waaaaaaayyyy lose. Is this bad? I know that the airflow will hold tension on the cable but what about when it's in a harrier? Will there be enough? I really don't want to move the horns...it would be a big pain in the butt. What do you guys think?

Post a picture with the rudder at full right or left showing the slack in the lose side.
This will help me to see what you are talking about. When your rudder is stright both sides should be without slack.
Roy

Hi 76...Here are the pics. These are the ones where the rudder is at neutral.

Here it's deflected all the way. On the first one you can see how much the wire has moved towards the middle. On the last one both of them are very loose sine there's nothing acting on the rudder.

I also have a question...When I put the arm on the servo it's not completely perpendicular to the servo when the servo is centered. What do you do in that case? Do you just leave it like that and then hook the rudder at neutral (i get a little bit of binding on one side) or do you trim it to be perfectly perpendicular and then hook the rudder (I noticed in this case the rudder doesn't have same travel both ways) Thx...

I would not worry too much about it. Just make sure the rudder has no slack at center, but not too tight. Just tight enough to take up all the slack. The air loading will push that rudder and only one cable will be effective when it's deflected at all. You just don't want the tail wagging when the rudder is center and you are flying (happens when there is slack at center).

Also unless you have programmable servos, you can only use the trim or subtrim to center that rudder servo. Again, it's no big deal if you lose a degree of rudder throw in order to center the servo. Go fly it and let us know how it goes. I'm sure it'll be fine. If you have a 40%r then maybe you want to get more technical about it. In that case go to SWB's website and he has a lot of knowledge on that site.

I agree with JoeAirPort,It looks pretty good. Let us know how she flys.
Roy
76.ta

Thanks guys. Will do...