Regarding building electromagnetic uncouplers: Many years ago I stumbled across an article in a very old Model Railroader, maybe from the late 50's. I'm sure you would never se this in recent mags! I built 12 of these for my yard, they work like a charm. It's been awhile and I forget some specifics, and have no idea where the mag is now, but a little experimentation should fill in the gaps. You start with a 1/1/2" long 1" steel pipe nipple. Clamp it in a vise, use a hacksaw to remove about 1/3rd of the nipples surface, so you wind up with a cross section resembling the letter c. At this point I did something not in the article, I used some Kapton tape to wrap around the nipple to prevent sharp edges from nicking the magnet wire to be wound on. I do not remember the size of the wire, it is small. Something like 23 or 25 (I found it odd that magnet wire used odd #"s) Wind it neatly working from one edge to the other, back and forth. Another thing I don't remember is how many turns. There are a lot! I basically filled mine up, perhaps a pencil could have fit in snugly. Wrap more tape around it to keep the windings in place. Oh, make sure you have kept several inches of the wire (both ends) handing out of the tape, to connect power to. That is basically it, I cut holes in the 3/4" plywood I use for subroadbed, and used that perforated steel straping to hold the magnet in the hole from below. The open section of the nipple must face up, of course, that is where the magnectic force is. And, it needs to be centered under the track, as I recall the edges of the cut pipe nipple wind up just about under each rail. This is cheap! Well, I did get the magnet wire free from work, so I'm not sure what its cost would have been.