[WIP] Signalbox Lever Frame with Interlocking

[Hod Carrier]

I'm unsure whether or not I should be posting this in this list or on the Technic list, but I guess that it's more topic-specific here. There are a lot of vehicles over on the Technic list, and that's fine. Technic LEGO probably best lends itself to constructing vehicles of various types and there are many fine and talented exponents of that art over there. But I did start wondering what else might be made from LEGO Technic; something without wheels, motors, PF or remote control.

After a bit of a brainstorm my mind settled on the good old-fashioned mechanical signalbox lever frame. There have been very few previous attempts at such a build (at least as far as I can tell from my research), so I thought it would be interesting to see if I could make some headway. I'm not terribly technically minded, but this was something that I do have a reasonable understanding of, and it's complicated enough to be challenging to design and build.

The starting point was to make the model fully functional and as realistic as possible, which means that any notions of scaling correctly would go out of the window (luckily that's an approach I'm very comfortable with). Therefore I wanted not just to have the lever frame but the interlocking frame too. Sadly Technic does not lend itself well to the conventional tappet method of interlocking, so I would have to devise my own system that did suit the medium better using sliding bars with pegs engaging with holes. I also wanted to include the catch plate mechanism on each lever.

Fortunately for my sanity I haven't kept a tally of the number of hours I spent brainstorming and then trying things out in LDD. As I said I'm not the most adept at technical matters, so this really has been a labour of love. However, I got there in the end and came up with a mechanism that looked good in digital form. Having done so I cast around for a prototype that I could recreate and settled upon Downham (the station is now called Downham Market, correctly reflecting the name of the town) between Ely and Kings Lynn in Norfolk as it was around 1974. It's a modest frame with 22 operational levers at this stage operating both points and signals. Downham at this time still had both an Up and Down yard as well as privately operated sidings, so it's an interesting location with lots of operational potential.

This is the LDD render of the lever and interlocking frames without the locking bars. My poor little netbook couldn't cope with the whole thing in one file so each had to be designed separately.

And this is the completed frame. It took a day and a half to assemble and, while 22 levers sounds quite modest (and is when compared to other locations on the network), the actual result is a bit of a monster. It looks more like a Wurlitzer organ than anything else.

A close-up view of the interlocking system. You can see how it should work with the pegs engaging with holes to either lock or release levers in the frame. The idea behind interlocking is to prevent collisions and other mishaps on the railways by physically stopping the signalman from operating certain points or signals.

This is the catch system on one of the levers. As is the case in a real signalbox, the lever must be released from the catch plate by operating the handle at the top of the lever before it can be pulled.

A signalman would be familiar with the position and function of all the levers in his signalbox, but just in case each one is colour coded (as per British practice) and identified by a plate.

There's more on my Flickr page.

So, does it work? Well, yes and no. But mostly no. The catch plate system works brilliantly. Admittedly because it uses a rubber band it can be forced, but it's not easy to do so.

But it's in the interlocking frame where things aren't so great. Part of this is because I designed the frame to be modular so that it can be expanded as required. A small prototype frame lead me to believe that the level of flex would be acceptable, but it turns out that at full size the flex is a significant problem. Luckily I designed the frame so that it could sit on baseplates which will almost completely eliminate flex altogether, and so I have some on order.

But the biggest problem is that the various parts of the interlocking system need to stay perfectly aligned in order for it to work properly, but they simply refuse to do so. Levers that are meant to be locked can still be operated while others that are meant to be released remain steadfastly jammed because the locking bars do not move as they are designed to do. Part of this is because the friction in the system needs tuning (for which I have replacement parts on order) but mostly because I underestimated what would be needed to keep all the parts in correct alignment. Therefore I've had to design structures to add to the frame that I hope will keep the various parts in line. The locking bars themselves still require a redesign in order to work with these modifications, but that is next on my list. Hopefully these remedies will be enough to have the frame working smoothly. If these fail to address the problems the next area of attention will be the sliding bars that drive the interlocking frame. After that I'll be out of ideas.

I hope you like it. I'm having a lot of fun with it and am proud of what is my largest MOC to date. There are more updates planned which I hope to reveal as time goes on.

Edited October 19, 2016 by Hod Carrier

[Man with a hat]

This is brilliant even though it doesn't completely function yet.

[Xris]

Hi,

your lever frame looks really nice. It looks like you can lock arbitrary combinations of levers in their positions, but did you try to model conditional dependencies between the levers (i.e. A can be set if B is set and C is not set)?

Regards

Xris

[Dread Pirate Rob]

This is a great idea. It is ideas like this that can make running trains more social:)

[Legotom]

Love this, brilliant engineering (as are real interlocked frames). I can't quite work out how the levers move the locking bars, can you show this? Is there a crank or something? Hope your new parts will get it working properly.

Hi,

your lever frame looks really nice. It looks like you can lock arbitrary combinations of levers in their positions, but did you try to model conditional dependencies between the levers (i.e. A can be set if B is set and C is not set)?

Regards

Xris

That is the whole idea of interlocking. To try and prevent conflicting moves being signalled. E.g you couldn't set the points for a train to cross a line unless that line was signalled at danger. All done mechanically in the original lever frame boxes, then by relays, and now by solid state electronics and software.

https://en.m.wikipedia.org/wiki/Interlocking

This is a mechanical box. The idea is that when a lever is moved to unlock a set of points or set a signal, it moves a locking bar across that locks or releases other levers. So in theory you can't set the points and signals in such a way so that two trains collide.

Edited September 10, 2016 by Legotom

[Hod Carrier]

Thanks for the feedback, guys.

It looks like you can lock arbitrary combinations of levers in their positions, but did you try to model conditional dependencies between the levers (i.e. A can be set if B is set and C is not set)?

Yes, the entire frame is built around conditional relationships between each lever and the locking bars have been designed to replicate these relationships. As I mentioned above, the frame is based on a specific location and is intended to be faithful in it's operation as well as capturing it's appearance. Using a track and signalling diagram that showed the type, number and location of the various assets under control from this signalbox as well as the order and function of the levers in the frame, I was able to work out the various interlocking relationships between the levers. I may not have got it 100% right, but I feel happy that the frame will work in a prototypically accurate way.

This is a great idea. It is ideas like this that can make running trains more social:)

Yes, that thought also crossed my mind, but there's a LOT more building to be done before I could be in a position to do that. There would certainly be vacancies for yard shunters to control the movement of trains in the yards as well as train drivers. It could be a great club activity.

I can't quite work out how the levers move the locking bars, can you show this? Is there a crank or something?

If you have a look at my Flickr feed you can see a few more photos which might help to explain it. I thought about using a crank, but I was never really happy. In the end I settled for an arrangement of sliding bars. It's a bit hard to explain in text and I don't currently have any photos of the relevant parts. However, I've done a bit of an LDD mash-up which I hope goes some way to answering your question.

The T-beam drives both the trans-clear beam and the blue sliding bar. The sliding bar is located in the diagonal gaps in the subframe using a pair of pegs so that when it's driven backwards by the lever it moves sideways as well as backwards.

The locking bar has a pair of prongs on the underside that sit either side of the sliding bar. As the sliding bar moves diagonally in the subframe this translates to sideways movement in the locking bar.

This design may still turn out to be unsuitable even if I can deal with the flex and alignment issues. We shall see.

Edited September 10, 2016 by Hod Carrier

[Xris]

Hi,

now I finally got it. The pictures of the transmission mechanism made it clear to me.

Thanks a lot!

Yes, the entire frame is built around conditional relationships between each lever and the locking bars have been designed to replicate these relationships. As I mentioned above, the frame is based on a specific location and is intended to be faithful in it's operation as well as capturing it's appearance. Using a track and signalling diagram that showed the type, number and location of the various assets under control from this signalbox as well as the order and function of the levers in the frame, I was able to work out the various interlocking relationships between the levers. I may not have got it 100% right, but I feel happy that the frame will work in a prototypically accurate way.

[Hod Carrier]

Happy to help.

[BricksMcgee]

Superb! Has been in my mind to build one to use during shows and displays, but the mechanics behind it have largely baffled me.

Thanks for posting!

[Hod Carrier]

You're welcome "Bricks". You might want to give me a chance to perfect the mechanism first before following my lead, but I'd be happy to help if needed.

[Hod Carrier]

A little update.

After tearing the frames down more than once and enduring a month of having parts strewn across my desk I have managed to get everything back together again and can report an improvement in reliability. The frame now sits on baseplates and has guide structures for some of the longer locking bars and individual lever bars. All of this, together with swapping out some parts, has helped to eliminate the flex in the frame and is helping to keep some of the key components accurately aligned which has helped to make the frame work better.

However, there are still issues with the way that the locking bars are thrown by the sliding bars that requires attention, so it appears that I still have some work to do. While the frame was in bits I did attempt a different drive method but it actually worked less well than the original design so I've gone back to that. There are also some issues that I feel are inherent to using LEGO as a building medium and may have to accept that there is little I can do about it, but maybe I can work around the problems. We shall see.

If I get a chance over the next few days I shall post up some photos of the revised design.

[archieg]

Excellent. It's nice and refreshing to see a non-vehicle Technic build.

[Hod Carrier]

Thanks Archie.

A few snaps as promised.

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[Sven J]

Very impressive!

I admittedly haven't much understanding of that aspect of railroading, but that only increases my respect for people like you who are able to conceive such devices!

[BricksMcgee]

On 9/11/2016 at 3:30 PM, Hod Carrier said:

You're welcome "Bricks". You might want to give me a chance to perfect the mechanism first before following my lead, but I'd be happy to help if needed.

Thanks - will likely be next year now anyway - I've got one big show left in me this year and I'm planning to start building for next year's displays.

[Hod Carrier]

Thanks guys. I'm still looking at it as a work in progress until such time that I can get the locking bars to work as designed. The shorter ones with fewer pegs work fine but some of the longer ones need a little push with a finger to make sure they go all the way across.

Richard: Are you going to be at Bricklive at the NEC? It's very close to where I live and I'm thinking of getting along at some point.

Edited October 21, 2016 by Hod Carrier