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Stour Valley Dream - Interlocked lever frame

Fen End Pit


Back in 2011 I played about with my Scalefour Society lever frame to use servos to lock the levers.


2011 blog entry


At the time I implemented the locking by connecting a PC and running JMRI, this used the 'logix' operation to monitor the state of each lever and then lock/unlock other levers appropriately. This worked OK but obviously required a PC to be connected to the layout. The locking was also based on my previous layout design rather than my current Stour Valley project.


Revisited the project over the last few months I had several goals.

1) fix the one broken locking tongue on one of the levers.

2) make interlocking correct for current project

3) remove the reliability on a connected PC by using programmable boards from the Model Electronics Railway Group (MERG)


The little tongue on the bottom of each lever makes the locking operate by passing through (or being locked by) the turning servo. On the first iteration of the frame I'd made these tongues rather small and one of them had broken off the bottom of the a lever. Rather than just replace the one broken one I decided to replace all 25 with a slightly large version. This meant lifting the frame 3mm further away from the servos and an additional packing layer was cut from 3mm perspex on the laser cutter.


The new lever tongue is about twice the width of the previous version and the additional size means that the part is much stronger. It also needs locks better against the servos.




The locking plan for Clare had been designed and thanks to input from Keith Norgrove we had a plan which only required simple 'AND' logic for the interlocking. By that I mean that all locking could be expressed in terms like 'lever 1 is unlocked if lever 2 is normal AND lever 3 is normal AND lever 4 is reversed'.


This form of locking could then by programmed using the MERG CANCOND board which listens to CBUS Events and generated an event when a condition is met. That event can then change the state of a servo locking or unlocking the appropriate levers.


It took a while to get the logic worked out but in the end I managed to sort it. Lots of head scratching and 'Its ON so I want to turn it OFF' mutterings and a large spreadsheet to keep tabs of the logic were required.


I put up a little demo video on youtube.




Since the video I had changed the labels on the levers to include their function and, in small but still vaguely readable text, the levers which are required to be pulled to release a given lever.




Some of those lever handles are getting a bit rusty now, I think the signalman needs to start using a rag to pull them.




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First class workmanship and an excellent explanatory video. The worked examples of the interlocking are clear and easy to understand, I'd recommend that to anyone who wanted to learn the basics of signalling. 


Building a lever frame is one of the things on my list for Kelvinbank and when I get round to it I will borrowing a few ideas, many thanks. 


Definitely needs some signalmans cloths though. Just think, something useful to make from all those superfluous hankies you get for Christmas ? 

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After watching the video, I looked up the MSE website and downloaded their assembly guide. They recommend tinning the handles - I guess it should be with lead-free solder?

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On 02/03/2020 at 03:04, BusDriverMan said:

After watching the video, I looked up the MSE website and downloaded their assembly guide. They recommend tinning the handles - I guess it should be with lead-free solder?

This was the Scalefour society frame rather than the MSE one, the handles are steel turnings and the rest of the lever is nickel-silver. I think you need a fairly aggressive flux and as much lead in the solder as legislation will allow.



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