St Catherine’s Lock, Shalford.
A year and a half ago, I decided to enter the DCC Concepts “Rodding” competition. I had been thinking for some time of extending my 00 Gauge layout to include the railway junction at Shalford and, alongside the junction, the St. Catherine’s Lock on the Wey and Arun Navigation. This was suggested by my wife as we have a narrowboat and have travelled through that lock on a number of occasions.
In the foreground is St Catherine’s Lock and in the background is the train from Redhill joining the main line from Havant to Guildford, taken in 2017.
Cramming everything into a 6ft by 2ft baseboard obviously required some compromises but, in general, the scenery went together quite well. The DCC Concepts scale rodding worked very well but I did make the mistake of trying to drive the signals with the same IP Digital point motors, which was definitely a mistake and cost too much time and effort.
The biggest problem that I had was the mechanism to drive the model narrowboat through the lock, opening and closing the gates and raising and lowering the “water” in the lock. At either end of the layout, there were turntables under small hills designed to turn the narrowboat around and sent it back through the lock.
I have usually found that trying to do something new and complex takes several attempts to get it right and, unfortunately, the time pressure to complete the layout by the competition deadline meant that there was only time for one go at getting it right – and it never really worked to my satisfaction. I did manage to film the narrowboat going through the lock for the final competition presentation but it took several attempts to get a clean run just in one direction. Trying to find solutions to problems, the mechanism became quite “Heath Robinson” and was never reliable.
Recently, during our enforced isolation, I decided to try to rebuild the mechanism and to make it work properly. One major advantage now, compared to 18 months ago, is that I have acquired an inexpensive 3D printer so that I can custom make parts as required. I designed and built gearboxes that sit under each lock gate to open and close them with adjustable limit switches. I designed and built a further gearbox that rotates a pair of M12 nuts to raise and lower the “water” in the lock. There are three drive motors, one above the lock, one in the lock and one below the lock, to drive the 6mm toothed belts that engage with the carrier that holds the magnet that pulls the narrowboat model along.
All the mounts and end bearings were also 3D printed along with the freewheeling pulleys. In all over 40 different parts, each one went through a number of iterations to get them right. One major advantage of a 3D printer is that if one part needs to be adjusted by 1 or 2mm, you can just adjust the drawing and reprint it.
The mechanism is built in three modules with the lock in the middle and the upstream and downstream modules as mirror images of each other. After a good month of constant incremental improvements to each module, the three modules could finally be run together on the bench.
While this was going on, I had to take all the old mechanism to pieces and remove the old “water” in the canal without damaging the rest of the model too much. Despite many layers of varnish and fine sanding in between, the old "water" surface was never slick enough for the narrowboat to move without jerking. At the Alexandra Palace show last year, I spoke to one group that had a lake with models sailing round it. They advised using Perspex as the “water” and “Gliss” powder to provide a friction free surface, so that is what I have done.
I also completely rebuilt the turntables at each end of the layout that turn the narrowboat around and reverses the direction of travel. Again this process went through several iterations until it worked reliably. One major change has been to use the brilliant DCC Concepts “Slim Vertical Mounted Magnetic Sensors” (DCP-TMS), which detect the magnet in the driving carriage under the narrowboat. This meant that it is possible to locate the boat very accurately at each stage of the process. As the detectors are "Normally Open", each one requires a relay to do the necessary switching. The turntable mechanism is hidden under a hill at each end.
Having painted and installed the Perspex “water” on the layout and mounted the mechanism underneath – many hours lying on my back under the layout adjusting everything – the canal element of the layout can now be left to run on its own with the model narrowboat going back and forth through the lock as the trains run past (the chuff-chuff in the video is the steam train not the narrowboat!).
There is still some cosmetic work to be done to repair the damage done to cut out the old “water” and to put some weeds to cover a couple of bolt heads - but the canal itself can now work away all on its own.
Its taken a while but it is great to have it working now.
All the best