View Full Version : Autopilot servo install
09-25-2007, 02:20 PM
I purchased a used Navaid AP-1, now I'm at the servo mounting stage. I am planning on installing it in the bellcrank bay and am trying to plan ahead if I need to remove/replace. Here's a couple of pic showing my proposed location. My question is:
1. How much stop to stop movement is in the bellcrank?
2. Do you think the angles for the A/P pushrod will workout?
09-25-2007, 03:00 PM
I put mine in my right wingtip (already flying plane).
Install was dead easy. Only "drawback" is the long pushrod. I used 5/8" 6061 tubing (I think that is it).
Total install from start to finish was under 4 hours, including pulling the floor and the new wires.
The force generated by the servo is pretty light, look at the wimpy little screws you get to put it all together with. I don't think the long pushrod is an issue.
P.S. DO NOT LOSE those #5/40 cap screws or nuts. You'll have _real_ fun finding replacements locally. :)
Oh, to answer your questions:
I measured about 2.125 inches (or so) for aileron bell crank movement. The Navaid has less.
I put my hole just short of dead center in the bell crank arm. IE, it is a wee bit closer to the spar than to the control tube.
The angle will not matter, as long as you can center the servo arm when the control stick is centered, and the servo has no possible way to get "over center".
You want your control stick to go stop to stop, without the servo touching either stop, if possible.
09-25-2007, 04:11 PM
That's almost exactly where I put my Gold Servo. I used some of the Z angle from the center tunnel cover to make some mounts. I placed the hole in the bellcrank as recommended by Trio basically the same distance from pivot points. I then adjusted the servo elevation on the rib to have the connecting rod close to parallel when in the neutral position. I'm not sure about the Navaid servo control rod, but I made a new rod of smaller diameter stock for clearance issues. I have hooked up the servo and it seems to work just fine.
09-25-2007, 04:25 PM
After flying for awhile I discovered that the servo had a problem because of the flex of the wing rib. I fixed this by beefing up the mount on the rib. This would have been a lot easier before closing up the wing.
The tell for this problem was to engage the AP on a bearing and then try to move the aileron by hand (on the ground of course). There should be no more then a 1/4 inch deflection in either direction before the servo stops you.
I have the following suggestion to beef up your current mount.
Install two angle pieces going full width from top to bottom of the rib and install platenuts on the out board side of the rib, so you won't have to deal with bolts/nuts through the lightening holes.
On the inboard side of the rib, next to the servo install another piece of aluminum to brace the rib fore and aft. I did this with two more angles with holes that go through the servo and then the angle and then the rib. This was also secured at the most aft end with a bolt through a platenut mounted on the outboard side of the rib.
It is not that the servo is going to break the ribs rivets, it is that you don't want any flexing of the servo mount or the AP will have trouble making the plane fly straight.
I have pictures somewhere, but can't find them now. If you want I will dig them up and post them.
09-25-2007, 10:23 PM
Sure is nice to have this site and being able to bounce ideas off of others. :) It's a real life/time saver for us remote builders.