Tuesday, 8 April 2008

Pictures of DCC AJ Coupling

In an earlier blog entry, I described the DCC Alex Jackson Coupling which I have been developing.

I've now taken some pictures of the first version, and present them here with some annotations. Clicking the pictures should cause them to appear much larger.

The first photograph is labelled to show the main elements.

  • (A) is the Alex Jackson coupling, formed from 0.010 guitar string.
  • (B) is a nickel silver u-shaped bracket which forms the support for the pivoting wire (A).
  • (C) is a steel counterweight. 2mm diameter, with a 12BA thread at one end. The thread is cross-drilled 0.3mm below the brass nut. When installed, the nut is wound down to clamp the counterweight onto the AJ wire (A). I have a better design for the counterweight which will be much easier to install than this first version.
  • (D) is the electromagnet coil, squeezed in behind a gearwheel which drives the locomotive jackshaft.

Because the locomotive is upside-down, the counterweight (C) falls to one side under gravity. When the right way up, it hangs vertically downwards.

This second photograph shows the same elements from the other side. The wires from the coil can be seen running over the jackshaft axle before heading inside the locomotive. There is a small piece of PCB mounted below the motor where the coupling wires are connected to the DCC chip wires.

The third picture has a propelling pencil holding the counter-weight approximately vertically. This shows the (approximate) rest position of the system if the loco was the correct way up.

The final picture shows the counterweight pulled over by the electromagnet. The counterweight strikes the side of the coil, not the iron core; this avoids it "sticking" when the electromagnet is turned off. An alternative to avoid "stick" is to cover one of the moving parts with something non-magnetic, such as a tiny piece of brass, thin paper, or even blob of glue.

There is massive scope to improve the engineering; the pivot would benefit from an etched design, the counterweight can be made much easier to install, and the coil pole pieces could be designed to deliver a more effective magnetic field. Even the use of Blu-Tac to fix the coil in place should be avoided in later version !

The locomotive is a High Level kit of a small Armstrong 0-4-0 diesel shunter (original at Shildon museum). Prior to fitting the couplings, it was assembled according to the instructions, with P4 wheels, simple beam compensation on one axle. The next loco to have a similar coupling fitted will be built up with the coupling in mind; its a lot easier to design space for parts before assembly !

Photographs taken with a Canon Powershot A710, with addition of a x4 and x2 close-up lenses fitted to a Canon accessory lense holder. The camera is on tripod, and taken with timer release. Its a pretty cheap setup for closeup work.

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