A plug in signal, Mk 1
Entry posted by Dave John
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I have managed to completely wreck two signals in my modelling career. On both occasions I caught the finial in the sleeve of a jumper and managed to bend them neatly over at 45 degrees. Trust me, lattice post signals do not bend back straight. As I age I realise that the more magnification you put on your head the less you know where your elbows are.
So, at the back of my mind has always been the idea of making signals which plug-in easily so they can be removed when working on the layout.
My list of requirements was thus. Firstly they should plug in and out without messing about with connections both electrical and mechanical under the board. Secondly I wanted them to have a small footprint, rather than them sitting on a plinth which could support a monumental statue of the Duke of Wellington. Thirdly I wanted both the signal and the lamp to work.
I had intended to do some design work for the stairs from the station building to the platform this week, but events distracted me from that. Last Friday at the SECC I had a good chat with Jim Watt who has produced some exquisitely detailed work in 2 mm scale, and I was admiring his signals which are fully working and plug in and out of a small baseplate. Then on Monday I happened to be in B&Q, and was surprised to find that they sell brass section. I was even more surprised to find that it was real brass rather than rather than some odd alloy covered in brass paint. So back home with with a metre of six millimetre by six millimetre brass and some eight millimetre angle.
Anyway, this is my Mark One plug-in Signal. The signal itself is an old one, just used here for the purposes of seeing whether the idea was at all feasible.
This is a picture of what I ended up with. All bits go inside the channel section which is soldered to the base of the signal. The key here is that the coupling between the the servo and the signal is magnetic, an idea I borrowed from Jim. The whole assembly is 75 mm long and could realistically be made a bit shorter. There are two 2 mm Circular magnets in the post itself, and a 10 millimetre by 5 millimetre magnet glued to the servo arm. The servodrive module here was made by embedded Controls, who are no longer about, but many others are now available.
The socket into which the signal fits is soldered up from brass Channel, the bit of copper clad and the nickel silver wire forms a contact for the led lamp. Since it is fitted from underneath the board and sits slightly shy of the top surface a layer of base scenic material can sit right under the signal.
The servo can he mounted anyway that is convenient. I made this with the open section of the channel to the front of the signal, clearly it could be made anyway round to suit a particular layout location.
Well, Here is a shot of what would be under the baseboard. The magnet on the servo arm does not actually touch the rear all the brass Channel, a gap of about a millimetre means that the signal can slide past the servo magnet easily.
A general Picture of the Signal, showing the small footprint, and one of it lit up. 
The whole thing can simply be pulled out to prevent accidents with jumpers.
Several modellers, including myself in the past have had problems with servos swinging wildly during the powering up phase. The torque produced by a servo is quite sufficient to damage a signal if it does. However one advantage of coupling the server to the signal magnetically is that the servo swing is not physically transmitted to the signal itself, so it can't damage it. Possibly a useful idea for coupling servos to mechanical devices in general.
I think that gives me the confidence to use this method for the actual signals that am going to build. As ever, all comments and suggestions welcome.
It was fun playing about on the bench again. Might sound silly, but getting in there with brass and solder is one of the most satisfying things I do.
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