This is probably getting way ahead of what I should be working on, but it's more structural stuff inside the fuselage that I figured I could knock out now.
I'm planning on doing a Garmin G3X Touch setup for my avionics, and just like the newer Dynon and MGL systems, they make it pretty easy to add an autopilot if you want to. All you need to do is figure out how to mount the servos to the controls, then run a wiring harness to them, and that's pretty much it. This will add a few pounds of weight, but I want to do lots of cross country flying so I think the extra convenience will be worth it.
The plan is to install a pitch servo and a roll servo. That will give me lateral and vertical control. I've seen some more complex setups with servos for yaw, trim, etc., but I think just these two axes will be fine for what I'm doing. For now I just bought one servo, since I'm just using it to design the mounting. I'll buy the second servo later when it's time to install them for good.
Anyway, Garmin sells servo mounting kits for a few Van's models, and Dynon sells mounting kits for the legacy Sonex, but I couldn't find anything pre-made for a Sonex/Waiex-B. I bought two generic mounting kits along with my one servo and went from there.
Here's the servo, with my hand for scale
Here's the servo attached to its mounting bracket
I'm starting with the pitch axis first. I had a few ideas about how to connect the servo to the elevator pushrod, either under the seat, just behind the seat, in the baggage compartment, or even attaching it to the control mixer back in the tail. I spent a while holding this servo and bracket up to various locations trying to decide what would work best. I preferred not to put it in the baggage compartment because I'd have to make a big cover for it or risk having loose objects get tangled up in it. I also didn't really like the idea of putting it way back in the tail for CG reasons. So that led to me to locate it under the seat.
The center bay under the seat contains the stick and elevator pushrod, but there isn't room for mush else. I wanted to somehow pass a linkage from the servo into that bay to either grab the elevator pushrod, or the stick itself. I found that the round lightening hole in the seat rib was a perfect spot to pass the servo arm through. I enlarged the hole into a rectangle, and that allowed me to set the servo in the next bay to the right, but have the arm pass through the hole right next to the elevator pushrod.
Once I got the position finalized I realized I could have kept that hole a little smaller. The reason I had to cut a rectangle beyond the round hole is that the servo comes with a stop plate that prevents the arm from rotating too far and going over center. It's not in the pictures, but it takes up a little extra space that I had to account for.
I wanted to attach the mounting bracket right up against the right side of that seat rib, but the flange on the rib that attaches it to the floor was in the way. I ended up doing something that in retrospect I don't recommend, and that was I pulled the floor off and just cut a few inches of that flange off so I could set the bracket right there on top of the floor and against the rib.
With the mounting location decided, next I had to create a pushrod. The mounting kit came with two rod end bearings and a piece of 3/8" solid aluminum rod.
I just eyeballed a spot on the side of the stick A-frame that I could bolt one end of the pushrod to, slightly above where the 1/4" bolt goes through to attach the elevator pushrod. I used the pitch trim to set the elevator control to a neutral position, set the servo arm vertical, and measured the distance. It was about 5.5". Given the nominal thread engagement specified for the rod ends, I figured out that the pushrod should be pretty close to 3/4" short of the mounting holes on each end (or a total of 1.5" shorter than the overall distance I measured). I went ahead and cut the supplied rod to 4".
Then I had to drill and tap each end of the pushrod. A lathe would be the correct tool for something like this, but I don't have a lathe. I figured out a way to get a decent result on the drill press though. First I clamped a chunk of wood to the drill press table, and locked in the table position. Then I drilled a 3/8" hole through the wood. I removed the 3/8" bit, without moving anything else, and then I knew the drill chuck was pretty well aligned with the hole in the wood. I inserted the rod through the hole, and fortunately it was a pretty tight fit. Then I chucked in a smaller bit and I was able to drill a pilot hole nice and straight into the end of the rod.
I did that on both ends, drilling up to a #21 bit. Then I clamped the rod in a vise and tapped both sides for 10-32 threads.
Finally I installed the pushrod! After a little adjusting, I could move the stick through its full fore-aft range without the servo arm running into its stops.
After that I went back and added two small pieces of angle stock to reinforce the floor around the servo bracket.
At this point I thought I was done, but I realized that that pushrod was installled a little too high on the stick. I didn't notice initially, but with the stick held aft, the bottom of the aileron bell crank interfered with the servo pushrod slightly if I tried to go full left aileron. Pretty much exactly the same problem I had when I tried to mount the trim spring higher than standard.
I needed to attach the servo pushrod slightly lower on the stick to make room, but the side of the A-frame was not flat any lower than where I already had it attached. I ended up making a little mounting tab that I could bolt to the A-frame, creating a new lower mounting point for the pushrod.
I had to shorten the pushrod by about 1/2", but with the new mounting point there was no more interference!
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