Yes, I built a controller fro G scale - 18v and 3 amps and it was successful except in one area, and that is the overload cut out. I used a normal car type of overload cut out which is probably too slow. Thus, on the rare occasion that a loco derailed on a turnout, and the overload tripped, something else went wrong with the electronics, and the unit only operated on top speed.
This also happened when I built it and 'tested' the overload cut out. At that time, I had a contractor working for me who had an electronics wizard on the team. He took it home, could see nothing obvious, dismantled it and then re-soldered all the components and it worked fine for 12 months until the derailment.
I then bought a Helmsman unit. When I subsequently spoke to Jeff Helm at an exhibition he said that the biggest challenge in making his controllers was the overload protection, and that he had to include a special circuit to get the speed of overload protection appropriate for G scale. It needs to be sufficiently insensitive for certain aspects of large scale running, but quicker acting than my car type re-setting overload protector (which I think is a simple bi-metallic strip).
Let us know how you get on.
