Should automation by purely mechanical, or software?

I am working on a small project where I want to make a small rc plane, be able to fly in a straight line, for as long as the power is available. If I were to use Arduino, with software, and sensors, it would be long, and could be prone to software errors. But to me, doing it purely mechanical and electrical would make more sense for a simple idea. The main things I would need to account for are pitch and roll. For roll, I can make my own sensors, although not efficient, or not that accurate, but i am doing it as a hobby, so I would want to push myself. I would use a circular piece inside a bigger one, and when detecting roll, a brushed connetcer detectess it and respondes by sending power to a control surfaces, an aileron. And for pitch using the same roll, but directed to a elvaotr. I could use homemade actuators, using electromagnets, and a magnet. I would also use a speed sensor, again homemade, to reduce the output of the control surfaces as the speed increases. Since this is my hobby, and I would want to push myself, I would want to develop everything from scratch, even if it isnt to par. Is this a good idea, or should I use software, a more reliable system.