How are articulated locomotives built?

[SteamSewnEmpire]

IRL, I know that most engines used a fixed rear wheelset and an independent foward truck. However, in Lego this seems like it would produce results that are neither attractive nor practical. Is the most common approach to treat both wheelsets essentially like big bogies with the body connected at two points above? Would the connection points be at the center of the two flanged drivers, rather than the center of the wheelset itself?

I have never done an articulated loco before, and don't want to start on the wrong foot.

 

*Edit* Here is a little diagram to better illustrate what I am talking about:

Edited August 3, 2020 by SteamSewnEmpire

[ALCO]

Depends on how long the boiler is and how much you want either end to overhang the track. I have one where the king-pin is directed between the flanged axles on one set of drivers and the other set the king-pin is off the last flanged axle by one stud. This setup is more a function of how much an end will overhang vs. Drive-line placement. There is no right or wrong way. My wheel arrangement is f-b-f-b + b-f-b-f. This arrangement was selected to get the pivot points of the leading and trailing trucks as close to the flanged axles as possible. But depending on your prototype and design you may need a different configuration. Just. My $.02.

Edited August 3, 2020 by ALCO

[SteamSewnEmpire]

21 minutes ago, ALCO said:

Depends on how long the boiler is and how much you want either end to overhang the track. I have one where the king-pin is directed between the flanged axles on one set of drivers and the other set the king-pin is off the last flanged axle by one stud. This setup is more a function of how much an end will overhang vs. Drive-line placement. There is no right or wrong way. My wheel arrangement is f-b-f-b + b-f-b-f. This arrangement was selected to get the pivot points of the leading and trailing trucks as close to the flanged axles as possible. But depending on your prototype and design you may need a different configuration. Just. My $.02.

Okay, thanks, that helps! I didn't know if there was some established pattern that people use that's more stable.

Has anyone done a fixed rear truck that worked?

[Daedalus304]

The "ideal" arrangement depends a lot on both your prototype and your layout. Fixed rear engines are definitely viable for shorter articulated engines, but your two most important factors for that are overhang and balance. Long articulated Locomotives with fixed rear engines absolutely can do some serious deforestation to your layout, and wipe out your second line at worst; unless of course you're running nothing but wide-radius turns. 

Finding the right way to articulate an engine takes a lot of work. In general, the further out your pivots are the less overhang you get, but it can make it harder to clear your pistons and detailing. You also need to balance the weight properly on your drivers, make sure the swinging engine works over height variances, curves, and a combination of the two.

If you're serious about building an articulated engine, you really won't be able to know what the best way to articulate it is unless you build a chassis and run it through some tests. That will make it apparent fairly quickly what sorts of clearances you need, give you an idea of overhang, let you know what your tracking characteristics are, and also let you get started on figuring out what power options work best. Powering both engines? Just one? Forward or rear? Pushing with the tender? Each of those options probably needs a slightly different system, especially once balance is involved. And it's tricky (though not at all impossible) to get an articulated Locomotive to track really reliably if you're pushing it.

[Craig Strader]

9 minutes ago, Daedalus304 said:

The "ideal" arrangement depends a lot on both your prototype and your layout. Fixed rear engines are definitely viable for shorter articulated engines, but your two most important factors for that are overhang and balance. Long articulated Locomotives with fixed rear engines absolutely can do some serious deforestation to your layout, and wipe out your second line at worst; unless of course you're running nothing but wide-radius turns. 

Finding the right way to articulate an engine takes a lot of work. In general, the further out your pivots are the less overhang you get, but it can make it harder to clear your pistons and detailing. You also need to balance the weight properly on your drivers, make sure the swinging engine works over height variances, curves, and a combination of the two.

If you're serious about building an articulated engine, you really won't be able to know what the best way to articulate it is unless you build a chassis and run it through some tests. That will make it apparent fairly quickly what sorts of clearances you need, give you an idea of overhang, let you know what your tracking characteristics are, and also let you get started on figuring out what power options work best. Powering both engines? Just one? Forward or rear? Pushing with the tender? Each of those options probably needs a slightly different system, especially once balance is involved. And it's tricky (though not at all impossible) to get an articulated Locomotive to track really reliably if you're pushing it.

It can be tricky, due to the fact that articulated locomotives are more elongated than just the average steam engine. But you could do the way I did it and have a fixed and free swinging unit, and use a f-b-f + b-f-f to allow it to accommodate even the tightest of turns if you get it right

[SavaTheAggie]

My favorite way is to pivot above the first set of drivers and above the rear truck.  This leaves the second set of drivers sliding freely beneath the boiler, being towed by the first set.

This is how my Allegheny is articulated.

mOxxLBa5N24

--Tony

[bogieman]

Very impressive Tony. Not too much swingout in the tight curves and switches.

How many motors are powering this? I couldn't see if the tender had standard train motors. Must be a bunch to handle that long train.

[SavaTheAggie]

15 hours ago, bogieman said:

Very impressive Tony. Not too much swingout in the tight curves and switches.

How many motors are powering this? I couldn't see if the tender had standard train motors. Must be a bunch to handle that long train.

My Allegheny is powered by two XL motors in the tender.

--Tony

[WRoberts316]

On 8/8/2020 at 4:39 AM, SavaTheAggie said:

My Allegheny is powered by two XL motors in the tender.

--Tony

Holy crap that is awesome!! Any tips for a newbie on building a proper chassis? I just picked up the new Hogwarts Express, and want to lengthen the engine to a more realistic length. Ill be powering it through the tender, but as an overall, I have no idea how to start, except in lengthening the tender to make the HUB fit properly.