WIP JNR C12 - seeking valve gear advice

[Srbandrews]

Afternoon everyone. I've been working on a MOC of a Japanese National Railway C12 2-6-2T in LDD:

Prototype looks like:

I've only coupled the rear two pairs of drivers to make space for gear if needed.

I'm really stuck with what to do with the valve gear here. I've seen lots of really intricate ones but generally can't quite work out how they've been put together. On the whole I'm also keen to avoid cutting up buts of tube and bars so a simple solution that captures the rough idea would definitely be preferable to something really accurate but involving much customisation. Any help or suggestions appreciated.

Edited February 7, 2015 by Srbandrews

[bjorkan]

I don't have an answer, but your model is great :)

[jtlan]

Nice model. I really like the use of the "grilled cheese" for the ladders on the boiler.

I don't typically model all the valve gear, but I like modeling the driving rods at least. Lately I've been using this technique, which @CommanderWolf and @SavaTheAggie used on their models of the PRR T1. Basically, it consists of a reversed tile sliding in a slot; the tile is joined to some technic half beams with a pin. Note that the model will be 8 studs wide (plus a plate maybe) at the cylinders.

If you send me the LDD file I can try to show you how it might fit on your model.

[Srbandrews]

Thanks guys! Cheers for the reference images jtlan. I must have seen that method used before but never noticed that it featured a sideways tile. I did a similar style of arrangement on my King class but using and axle as piston like the Emerald Night. What I could do with is something that looks a little bit more complicated, like a walschaerts gear, without being too fiddly. I guess I'm asking a lot there...

[greenmtvince]

Are you staying purely Lego? There's a lot of good options if you use Zephyr's custom valve gear and drive rods.

[zephyr1934]

While I certainly do think that Zephyr's rods are keen, if you keep it pure lego I think something like the rods on this moc are a pretty good solution... oh, and while I like the cylinders in that design, the "piston" design from Cale is REALLY simple and runs very well, e.g., as used in this MOD, with more details here.

[LEGO Train 12 Volts]

You could redesign the cylinders like Reinhard Ben Beneke did:

[Srbandrews]

Thanks for the suggestions.

While I certainly do think that Zephyr's rods are keen, if you keep it pure lego I think something like the rods on this moc are a pretty good solution... oh, and while I like the cylinders in that design, the "piston" design from Cale is REALLY simple and runs very well, e.g., as used in this MOD, with more details here.

I really like the second one here but am a bit confused about something in spite of the instructions. Your rods Zephyr I assume are the width of a thin liftarm, so does the main rod not have to bend out a bit in order to be ouside the bars that the pin slides between?

[zephyr1934]

My rods are 3.5 mm thick while a thin lift arm is 4 mm thick and a plate is 3.2 mm tall. This odd thickness in the rods arises from omitting the pin cuffs on one side and allows them to float on the technic pin heads. It also allows the rod to bend outward like the photo in my last post. You cannot (easily?) replicate that design with thin liftarms because the side rod is 9 long and the longest lego thin liftarm is 7 long. You can do it with thick lift arms or technic connectors (both are the same thickness) and that eliminates the need for bending the connecting rod. I think in this case a 3/4 pin works, but it might need a full pin.

[Srbandrews]

Ah, that's useful to know. Thanks Zephyr. I've decided to take this build 'to the physical stage' and have ordered a load of parts, including a miscellany of liftarms both thin and thick to experiment with. However, I do think that of all possible projects this is the most likely to convince me to go custom with the valve gear. Hard to imagine a satistying purist solution.

[Srbandrews]

Going for the pin between two bars method. Here's how it looks after the first bricklink order. The rest should be here soon, I hope.

Japanese C12 WIP by Srbandrews, on Flickr

[LEGO Train 12 Volts]

Nice upgrade!

I'm looking for your next step!

[Srbandrews]

Thanks! And finally the valve gear is in place. It works perfectly but it does seem to sag out to the sides a little bit. I guess this must be the same for everyone who used the same technique though:

C12 Pretty much finished by Srbandrews, on Flickr

C12 pretty much finished by Srbandrews, on Flickr

C12 Pretty much finished by Srbandrews, on Flickr

I think now I just need to add some small locomotive number stickers and tweak a couple of details and I'll be there.

Edited February 15, 2015 by Srbandrews

[LEGO Train 12 Volts]

Hey very nice!

Mission accomplished!

[zephyr1934]

Looking good!

[jtlan]

Srbandrews, you might consider replacing the dkgrey pin at the end of the 5L liftarm with a half-pin, with the long side of the pin plugged into the liftarm and the "lip" of the pin behind the dkgrey rods. The lip will keep the liftarm from sliding outwards.

[Srbandrews]

Srbandrews, you might consider replacing the dkgrey pin at the end of the 5L liftarm with a half-pin, with the long side of the pin plugged into the liftarm and the "lip" of the pin behind the dkgrey rods. The lip will keep the liftarm from sliding outwards.

Aha, thank you. That works quite nicely.

One thing I haven't mentioned is how much of a tough time I've had making the articulation of the front and back axles work how I wanted it to. Finally I think I've cracked it and got it taking corners smoothly.

Quick video of it running:

It's really difficult holding the phone steady and operating the PF remote.

[Srbandrews]

Sorry to bump, but I've been puzzling over this for a while and wanted to share the results with which I'm quite pleased. This may have been thought of before but I don't think I've seen it. By adding the light grey connector, I've essentially lengthened the useful length of the 'cylinder' while trying to disguise it as part of the valve gear. Runs really smoothly and doesn't poke out at the front too much to get in the way of the wheels.

And a short clip of the motion

http://youtu.be/Eq1ILNiXJu0

Edited February 25, 2015 by Srbandrews