Like Poles Repel

Another long pause in activity following my participation in the Channel 5 'Great Model Railway Challenge'. Having completed our heat, and then being in the final, we were asked to build another layout for the Radio Times. Then, Peco invited us to have our Santa layout on their stand at Warley, which was followed by a visit to Bognor Regis. Finally, I could get back to worrying about Freshwater, with two shows in February, Stafford and Tonbridge.
 
As reported earlier, I use small 'rare earth' magnets for operating DG couplings. I mounted three magnets on a bar that is moved by a servo so the bar covers three parallel tracks. This gives me 9 uncoupling positions for the cost of 3 servos. However, two positions near the centre of the layout were always a bit temperamental, managing to uncouple some wagons but not others. I put up with this for some time, but for the Stafford show, I had inadvertently left my stock box at home. None of the few odd wagons we had with us would uncouple there, so I had to try to fix the problem before going to Tonbridge.
 
I had checked many times that the magnets were moving to the correct position, centrally below the tracks, so I toyed with the idea of adding a couple more magnets to boost the magnetic field. Then I had a brainwave. This uncoupling position was close to the frog of a point, so two magnets were quite close together. I used another magnet to check, and found that I had one magnet with its north pole on top, and one with its south pole on top. Being so close to each other, the magnetic field was taking a short cut between the magnets instead of going up through the tracks. I turned one of the magnets round, and uncoupling was reliable for the Tonbridge show.
 
It only took me 10 years to rectify this problem.