With the pitch axis pretty well figured out, I removed the servo from that bracket and reused it to set up the roll axis. Space was less critical for this one, but it had its own different challenges.
First, I knew I wanted to locate the roll servo in one of the outboard bays under the seat. I decided on the right bay since it'll be close to the pitch servo, making the wiring easier. There's plenty of room there, I just had to figure out how to attach a pushrod to either the bell crank on the stick, or the right aileron pushrod.
I figured I locate the servo approximately here:
My next consideration was making sure the servo would be able to move the ailerons through their full range of motion. This was a little uncertain without having the wings installed. I took a look at one of the long aileron pushrods installed in a wing. I found that the farthest the aileron could travel up and down would move the pushrod a total of about 4-3/8" in and out.
Based on that, I decided I should plan on being able to move the aileron pushrods about 2-1/4" either way from center.
The servo motor includes a travel-limiting stop that prevents the servo arm from going over-center, which can result in pretty much irreversibly jammed controls in flight. The bracket allows the servo to rotate no more than 50 degrees in either direction.
So I needed 2.25" of travel at no more than a 50-degree angle... Some trigonometry told me that I needed a lever arm around 3" long. The standard crank arm that came with the servo is only 1.5" at it's longest hole, and the "long crank arm" is 2", so I decided I just needed to make a longer crank arm.
Using the crank arm I had as a template, I traced out a version on a piece of 1/8" aluminum and extended it to place holes at 3", 3.25", and 3.5".
The new crank arm is quite a bit taller than the motor itself, so I had to make sure it would still fit under the seat. Luckily the seat slopes upward pretty steeply as it goes forward, so as long as I mounted the servo no farther aft than where it is here, the arm wouldn't hit the seat bottom.
Here's another view:
Next I had to figure out how to connect the other end of the pushrod to the ailerons. My initial plan when I started was to just use a longer bolt and attach it to the same hole as the rod end bearing of the right aileron pushrod, at the bottom of the bellcrank on the stick. That's why I planned on making the servo cover the whole 4-3/8" of travel. After looking at it for a while I realized there was plenty of space on the stick bellcrank above where the aileron pushrods connect. This would be simper to attach, and it moved the servo pushrod attachment point closer to the pivot, which means it wouldn't need to move as far to move the ailerons through their full range.
This new attachment point is about 1" closer to the pivot axis, so it doesn't move as far left and right as the aileron pushrods themselves. Now I only need the servo to travel about 1.75" in either direction, instead of 2.25". Doing some more math, I found I could shorten my crank arm quite a bit and still provide the full range of motion without exceeding 50 degrees of servo travel.
Now I only need about a 2.5" long servo crank arm, so I drilled more holes and test fit everything again. It works!
Finally, I installed the seat to make sure nothing interfered with it. I noticed that the bellcrank on the stick runs into the edges of the cutout in the seat before anything else. I asked Sonex what is supposed to limit the ailerons' travel, and the answer was not the seat pan. I think with both wings installed and the ailerons rigged correctly, each aileron will limit the travel of the other. Bottom line, I think I planned to accomodate a little more travel than I needed. Once I have the wings on I'll check again and I might be able to shorten the servo crank arm even more.
For now though, everything seems to work fine without any interference. I drilled the roll servo bracket to the floor, and then pulled the floor off to finally clean up the huge hole I cut in the seat rib for the pitch servo.
I also riveted the roll servo bracket in place, along with some small reinforcement angles like I did for the pitch servo.
I'm calling this project done until later when the wings are installed!
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