28/09/06: Below Decks

Progress has been mostly ‘below decks’ on the roundabout board.

Point motors have been fitted to the railway crossover. These are Peco items fixed to the baseboard rather than to the point - this gives a much smaller hole to conceal. Click here for details.

Magnetic stops have been installed at each entrance to the roundabout and road junction. In order to give the operator a hint as to their status I have fitted reed switches linked to LEDs to warn when the magnet is in the 'stop' position. I hope to devise a similar system for the road junctions which will make life a lot easier. Unlike railway points there is no way to check which way a junction is set without either running a vehicle through it or peering under the baseboard.

To add to the rat’s nest of wires under the baseboard I have also started putting in the hall effect sensors to detect passing vehicles. These are activated by the magnets on the steering arms. Unfortunately despite early experiments it appears that the sensors need two magnets on the steering arm for reliable operation. I have doubled up the magnet on the S17 but the Transit just can't move against that force so it may have to have a separate rare earth magnet fitted elsewhere on its chassis.

The first of the RFId readers has been installed and is a complete success. A small (3mm long) glass tag mounted on the vehicle‘s chassis allows the reader to identify any passing vehicle and pass the information to a PC via an RS-232 link.

eBay has provided a device, yet to be installed, to hang 16 RS-232 lines off the PC which will be enough for the whole layout.

The wiring colour code has thus expanded. New colours are: Black - ground for reed switches and hall effect sensors (also used for railway point frog power feeds); Red - +5V power for hall effect sensors; Grey - Signals from reed switches and hall effect sensors. Whilst the use of black for two different functions is not great, I showed lack of foresight when I used it for the point feeds. I shall change the point feeds to green on other boards.

The trusty S17 was rendered hors de combat by a rear wheel slipping on the axle. A drop of superglue soon fixed it. The LS18 is still over the pits awaiting attention to its motor.

It is interesting to see the different way that road vehicles behave compared to trains. The wheels on a train all follow exactly the same path (unless it is in the process of coming off the rails of course). With road vehicles the front axle follows the guide wire but the rear axle takes the shortest path towards the front axle, as shown in the photo above. If you don’t take this into account when laying the guide wire and setting out pavements you could well find yourself in trouble as passing vehicles swipe each other and hit the kerb. The longer the vehicle, the more room it takes. This is why bus and lorry drivers will pull out of a side road like this:

Now, if you wanted to be clever I suppose you could arrange two guide wires, one for cars and vans, the other for lorries and buses, so that they could exhibit the correct behaviour at junctions - but that could get rather complicated. I have adopted the policy of leaving enough room for a 36’ bus to trundle around without hitting anything. Speed is another factor; it is a lot easier to make a tight turn at a walking pace than it is at 70 mph.

Above ground level I have mocked up the car park that will be at the end of the layout and started on the red-brick pile that will be on the other side of Back Road. The car park is based loosely on the Swan Centre in Kidderminster whilst the red-brick building is a Heljan Synagogue kit.

This is an HO scale model but is large enough to still be imposing in 4mm scale. Costing less than £15 including shipping from Walthers in the US it is now also available from Kittle Hobby as their Town House kit. I have chopped a bit off the back to get it to fit in the available space. There are three possibilities for its use on Redhill - a police station, post office or library. The jury is out on that one.

As followers of this saga will know the name and design of Redhill are purely the product of my own fevered imagination - so I was astounded to find that the roundabout area closely resembles the Belfry roundabout in, you've guessed it, Redhill. The arrow on the map points to where I was standing to take the photo at the top of the page!

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