Moveable Magnetic Uncoupling Ramp
I am using the large permanent magnets by Kadee or Bachmann, cut to half length, under the track in yard tracks where uncoupling is pretty regular. On the mains and sidings I use a sliding magnet buried under the track, common in use in the Omaha area, pioneered in this area by Jeff Otto. It works on the principle that a undertrack magnet only works if the magnet is centered under the track. If the magnet is just a 1/4" or so off center the magnet will not uncouple the cars. The magnet is slid back and forth in a slot under the track to activate and deactivate the uncoupling ramp.
A slot is milled in the roadbed about 7/16 inch deep (enough to that 3/8 Plastruct angle and a piece of .010 plastic sheet will just come up to the bottom of the ties. ) It is as long as a half length magnet plus a tad more than the twice the thickness of the Plastruct angle legs. It as wide as the width of the magnet, plus about 3/8 more to one side (preferrably to the off side of the track).
Two pieces of Plastruct 3/8 angle are cut to fit and glued in the slot. A piece of thin plastic sheet, narrower than the distance between the two angles, is ACCd to the bottom of the magnet. It is wider than the magnet by about 1/4". The portion that extends beyond the magnet has a narrow slot cut in it. A hole is drilled verticaly through the roadbed on the off end of the slot close to one of the angles. A piece of brass rod is bent to a zee shape and put in the hole. The slot in the plastic under the magnet fits over the brass rod. Adjust the travel so that the magnet just uncouples cars when the magnet is moved to the near side of the tracks. Drive a nail or spike into the roadbed to limit the travel to the near side in the uncoupling position. Bend the portion of the brass rod under the layout in such a position that when a person standing in the aisle pulls on the rod it slides the magnet into the uncoupling position and when a person standing in the aisle pushes on the rod, it moves it out of the uncoupling position. Cover the slot area with .010 plastic sheet. I usually then cover all the edges of the slot with masking tape to seal it shut and keep ballast out. A friend of mine uses 1/64 model aircraft plywood as a cover instead, because he had problems with the ballast coming loose off the plastic sheet. You can then use a push rod (brass rod or dowel) through the fascia to activate the uncoupling ramp manually or hook up a switch machine or motor to it for remote or powered operation.