After a season of flying the extra special 300 in IMAC I'm ready to start 3d'ing this bird. I was using the little 3/4 inch servo horns from hitec and they wouldn't give me enough throw on my elevator. I'm building a comp arf right now and I didn't need the phenolics so I decided to build two for the elevator servos. The geometry looks weird... Will this be ok? The servo horns are just over and inch and the control surface linkage is about an 1/8 longer than the servo horn from the pivot point.

It just seems strange. Is anyone else doing something different for the throws needed for 3d??

Get some 1.25" arms from either airwild or swb and turn them upside down. You have the old version of the plane so your servos are in a different place, but here is mine.

I can turn mine upside down too. Would that be a better idea? Mine are not that far back as you said. Would there be more mechanical advantage that way?

CRaig

Your servos are more further back than mine. Try turning them upside down, but you may need to make some new pushrods. Also, measure the length from the center of where the arm attaches to the servo to the where the pushrod attaches. It may be the length of that distance that is limiting you. You could try to find the servo arms (the long black ones) that come with the servos if those are 5945's. Another option, which may be the best route for you, is to just pick up some DuBro HD servo arms from the hobby store. They're cheaper than the airwild and swb and plenty strong.

Ben,

Thanks for your help. I'm getting plenty of throw with the arms that are on there now. 40 degrees up and down and I hope that is enough. I'm wondering if the setup is ok though. Because of the servo arangement the rod is angled when at neutral.

Craig

40 degrees should be pretty good.

There are a couple of different schools of thought here. Some people say the rod should be in a straight line when the servo is at neutral. Some say it should be in a straight line at full deflection. I tend to go with the latter train of thought in which case your setup would be fine. One thing I do do though, 'specially on aileron servos (but I do it on all servos, even throttle) is to put a ball link on the servo arm end of the linkage. Helps tp prevent binding as the servo moves throughout its range of travel.

psk560,

There were two positions for the elevator servo's older and newer. I believ with older version, 1 1/4" is max servo arm length. Might want to check that also.

On the older Edge/Extra, the longest servo arm you can use at the elevators and have them pointed up is 1-1/8". That length is more than enough for excellent 3D. If you have a rudder servo mounted in the tail, the same length arm, 1-1/8", mounted pointing down, is also as much as you will need.

I strongly suggest that you obtain a good set of aluminum servo arms in the appropriate length, along with strong, close fitting connectors that have both excellent range and freedom of motion. I'm partial to Nelson/Rocket City RCL70 stuff (www.nelsonhobby.com). Others like JR or Dubro. Both SWB and Airwild produce excellent servo arms in the lengths you will require. The stock, short Hitec arms won't be able to do the job for 3D no matter what you do.

Pat

Thanks guys. All the comments are great. I'll get some aluminum arms soon.

The geometry is ok though so that is kewl.

Craig