I purchased the NavAid Autopilot System. When I got the unit several months ago, a quick bench test found a few electrical problems. I sent it back and they did a quick turn around with a new unit. They were excellent to work with and I love the unit. There are 2 basic parts, a cockpit unit I'll call the "brain", and the servo that moves the aileron. There are several installation methods for the servo. Since my wings were in process, this made the fitting into the wing very easy, and very solid. Others have done an under the seat method, as well as a wingtip method. Naturally mines the best:) , but others will work too. (see Sam's wingtip method)
The brain consists of a cockpit mounted unit that has an electric gyro in it to be able to tell when the plane is banking. The unit only controls one axis of the plane, namely the bank. Pitch control is still left up to you. The unit also doubles as a turn coordinator, and a very nice one I might add. I really like the LED readout. And the most geeky fun part is this thing, wired to a GPS, will track a course. How's that for slick!! Tell your GPS to take me to Oshkosh, and your there hands free. I have a hand held Garmin III pilot which will do the trick. To the left is the brain, to the right is my GPS which works great. I highly recommend this GPS for its ease of use, accuracy, low cost, and built in pilot features. Pictures link you to products also.
On to the servo.. Here is a shot of the servo, mounted into the wing, very close to the aileron bell crank. A couple of rails installed between to ribs does the trick. It will come out the access panel w/o difficulty as I have taken mine out twice for testing wiring. Also notice the rail will be riveted to skin giving this some serious rigidity. The arm is only a couple inches long to the bell crank giving no play that I could measure. (sorry for the poor pictures, digital camera does lousy up close for some reason.)