technic L gauge with fully working valvegear

[Aerolight]

Greetings train forum, I mainly frequent the technic forum but thought this might be a better fit here, due to something I am stuck away from my Lego (at my grand parents) for a while so no pics or updates for a while but was feeling down and though some of you might appreciate the ensuing wall of text that would annoy the technic goers not end. 

First I wanted to have a realistically working pneumatic train (I like to think we have all liked to believe such a thing could work at some point), while as you can imagine the pneumatic switches where, even after modifying, just too stiff to work smoothly at all let alone with all the links I was driving them through. But for this I first built a valve gear using a sliding block design (idk what you would call the system as it did not use a 90 drive (too week and too wide) off the wheels but used a different link system to account for it). 

While this system worked it was too big both in height and width (4 wide each side and about 10 studs off the tracks). But then I remembered baker valve gear, at first I had discounted it as it is more complex; but in Lego form while still more complex its far smaller EVEN SCALE for a larger shunter. However I did have to cut down most of the beams for it as it used strange half stud pieces i.e. 3 studs half thick with a cross at one end and a pin at the other.

So then I mounted it in my train chassis and mounted the servo that controls it(I'm using power functions so servo had to be gear down twice to reduce the movement to +- 35 degrees-ish and insure neutral was completely level). This first prototype had the baker part of the gear outside the wheels and was 10 wide (the baker system requires a minimum of 4 rods to over lap so with half stud beams 2 studs either side) and a 10 wide expansion joint. 

This first prototype worked perfectly, as you increased the speed of the loco the servo would actuate the control link and the valve would open more and more to a maximum just over that of scale valve movement. It worked in both directions with no clicking clucking or increase in friction and looked amazing while doing so I think it might have been a first in Lego but even in the model space I know of few that have realistic working RC valve gear. The only problem was that due to the loco moving at the lowest increments on the speed controller the servo would move so little that combined with the slack in the links the valve movement at slow speeds is negligible.

Next I moved the baker on top of the wheels allowing for it to be 8 wide at that point whilst not being any higher (I spaced the drive wheels out 1 stud to give clearance and also deleted the suspension (technic rubber 1x2s) for space) but I could only reduce the expansion link to 9 studs as it still has to be above the connecting rod and cylinder drive rod. 

This current version (not including the motors as they are central and can be easily covered) is 9 studs wide and about 6 studs high from the track (sorry memory) and drives great with a 4 wheel bogie at the back underneath the drive motor (L) and a tender holding the battery. But I don't know how to add a front bogie, I tried to raise the pistons to give space but it looked strange and if I have to move the pistons further out it would be 10 studs wide which also looks strange. Hopefully a easily solution will come to mind next time I see it but until then this is where the MOC currently stands; fully driving but no front bogie or coupling, no body (that comes last right?) and valve gear only on one side (I wanted to make sure it was finalised before I cut any more pieces. 

Along with simply finishing it in its current form I hope to rebuild it with control+, along with being more controllable, allowing me to fix the issue of pulling away in neutral, the servo is smaller and will not require extra reduction. This would give me the space for a cab with perhaps a moving leaver (sorry forget name) tied to the servo. 

Again sorry for the lack of pictures and poor explanations, but I will try to answer any questions.

[HRBuildNStuf]

While it doesn't allow me to get the connecting rods themselves down below the top of the wheels, by creating a sort of "sled" just using liftarms that at least hollowed out the space between the wheels a little bit so that the piston housings themselves could dip down below that wheel line by sitting between the front and back wheels of the bogie. Its connection point is in the rear, so it's not attached to the superstructure above it but to the chassis behind it. I don't know if that'll be helpful at all, but for me it helped a lot with the aesthetics while still allowing me to have a fully articulated chassis.

http://onedrive.live.com/?authkey=!ADTgaBG0eHArPgU&cid=68647F36576FACB2&id=68647F36576FACB2!117618&parId=68647F36576FACB2!117595&o=OneUp 
http://onedrive.live.com/?authkey=!AE5RaB3Zs2iA3e8&cid=68647F36576FACB2&id=68647F36576FACB2!117619&parId=68647F36576FACB2!117595&o=OneUp
http://onedrive.live.com/?authkey=!AAGSfrOC9Q9lq14&cid=68647F36576FACB2&id=68647F36576FACB2!117617&parId=68647F36576FACB2!117595&o=OneUp
http://onedrive.live.com/?authkey=!AKF39g45F5kwTg8&cid=68647F36576FACB2&id=68647F36576FACB2!117620&parId=68647F36576FACB2!117595&o=OneUp
http://onedrive.live.com/?authkey=!AK93N0sjG4gj2Z0&cid=68647F36576FACB2&id=68647F36576FACB2!117621&parId=68647F36576FACB2!117595&o=OneUp
http://onedrive.live.com/?authkey=!AHFgCIucNdnhYRQ&cid=68647F36576FACB2&id=68647F36576FACB2!117624&parId=68647F36576FACB2!117595&o=OneUp

By having a pivot point right where the back pair of wheels are, they don't need to swing very far left to right. The rest of the bogie then does need to slide left and right, but then all of that wide-swinging bit sits below and in front of the pistons

Another idea might be to make the wheels in front of the pistons independent; they could maybe have a pin that slides in a track horizontally left and right. Not sure what to do with the wheels behind the pistons, they're the real problem if you want them to articulate but not cut into the driving rods.

Edited April 5, 2020 by HRBuildNStuf

[Aerolight]

Finally I can give an update, restrictions have lessened so back to lego next week.

On the boring side I think the best way to have the front wheels is to have 2 on a very long link, looks a bit derpy but works.

However after seeing someone make a pneumatic engine with a new type of valve, I'm going to take one last shot at pneumatics. This new valve works by kinking lego hose and requires barely any force to operate; compared to lego switches at least. If it ends up still being too much for the realistic valve gear to operate then I've got an idea, I can drive the valve links via the cylinders directly rather than from the wheel at the end of the array; which incurs a lot of slack.

Hopefully the next update will have a video with a healthy chuffing sound, if not then finally a video of the dancing valve gear.