[MOC/WiP] China Railways QJ with PF!

[Commander Wolf]

EDIT: This model has gone through a lot of revisions over the years and much of the info in this thread is outdated. This video shows the latest version and provides a link to instructions on Rebrickable:

 

 

Spoiler

Hi, all! After piddling around with some small projects for the past few months, I decided it was time for a challenge!

I'm building a Power Functions steam locomotive where the locomotive is powered (as opposed to a tender). To make things harder, the prototype isn't some small shunter, but the 2-10-2 China Railways QJ:

The QJ is a fairly large mainline engine whose roots can be traced back to the various German 2-10-0s used extensively during WWII. Its primary claim to fame is probably the longevity of the design and quantity of units built - 4700 between 1956 and 1988. The QJ was used extensively on Chinese mainlines throughout the latter half of the 20th century, and a few soldered on in revenue service toward the end of the 2000s. Three survive in the US, two owned by Iowa Interstate, and one by RJ Corman.

Anyway, I've decided to do a log of the build and share some of the process. We'll see how this goes.

As always, the first step for me is finding drawings. I had previously wanted to try my hand at some smaller Chinese locos like the SY or JS, but having not found any drawings, the QJ was it. Resized to my usual scale of 15" per stud, it looks like this:

The next task is to decide on the layout of the chassis. The "obvious" way to do it would be Emerald Night style - 2-10-2 with a blind-flange-blind-flange-blind configuration for the 10-coupled section, but this method results in a lot of overhang on curves, especially so if the body is attached directly to the 10-coupled section, and I really don't like that. That and other issues with the 10-coupled arrangement led me to look at more fun (complicated) designs, and I eventually settled on the following:

This is a 2-2-4-4-2 articulation where the cylinders are actually locked to the middle 4 wheels because that's where the drive rods will connect. This arrangement lets me have driving and connecting rods across all flanged drivers, which I really like, and this also keeps the maximum width of the chassis at 9 studs at the cylinders. Yes, the 3rd and 4th axles aren't visually connected, but I would prefer having a gap over a thick or uneven connecting rod (full/overlapped half beams).

At this point I had a vague idea of how I'd connect everything together, so I dumped it into LDD to sketch out the overall shape.

Here I've just thrown together my intial thoughts of how I'd build various parts of the loco just to line things up with the drawing and evaluate the overall look and feel. I start like this because to me it's much more important that the overall proportions of a locomotive are correct and less important that individual details are all modeled.

Now we can start on the detailed design. The first issue I tackled was the all-important method by which I'd connect all the axles that weren't already linked with connecting rods. To that end, I had known I would probably use a mechanism I had already used multiple times in the past, but I spent a lot of time trying to make it more rigid and compact. I also discovered how much easier it is to compact various assemblies by going to an all-studless chassis.

Next up, connecting motors to the now coupled drivers. This has proven to be by far the most difficult part so far. One of the things that's really important to me is minimizing the overhang of the locomotive body inside and outside when it goes around a curve. To adjust this, you can move where the body pivots on the chassis (typically two points, one toward the front and one toward the rear - on a diesel these are the points at which the body connects to the bogies) forward and backward. The catch is, now the drivetrain connecting the motors to the wheels has to flex through these points as well. I settled on an initial design like this:

As you can see, the drive train comes up from the last driven axle through the point at which the trailing axle is connected. Then it goes backward and there's a univeral joint through the point at which the body is connected to the last axle. How the motors are supposed to be joined to each other and to the wheels is still unclear here.

At this point, I decided to make a mockup and do a test run, because you never know if things you make in LDD are going to work in reality or not.

In this case, it did not.

Turns out that the joint above the last driven axle was far too flimsy, and trying to transmit any significant amount of torque through it would throw the rear drivers off the track.

And so here I am at the moment:

This is actually the first design that made it around my test track, and it seems to do so fairly reliably for now. You can see the (yellow) more rigid redesign of the flimsy transmission and the (orange) more detailed design of the first driven axle. The actual testbed is not quite as pretty colored:

More updates to come, stay tuned!

 

 

Edited January 5, 2022 by Commander Wolf

[LEGO Train 12 Volts]

Commander I think that your works are amazing ...and the technique of this locomotive looks great as all your MOCs!

[Redimus]

I was going to suggest flangless wheels but you've already ruled those out. How about doing what I've seen done on a lot of German loco Lego builds, using the same rods you've used for the connecting rod for the coupling rods. Those bars may be flexible enough for you to still have the pivot. Alternatively, perhaps using those bars in tubs, with the joint set being 2 smaller bars with one tub over them to give a more flexible joint.

Otherwise it's looking good,but I just can't bare the sight of a loco that isn't properly rodded up! lol

[Commander Wolf]

Well, been a little distracted from this project, but managed to make some progress the last few days.

Worked on polishing up the chassis including detailing the front and back trucks:

On the back truck I couldn't think of a way to get a rounded corner on each side of the frame over the bearing, so that's kind of annoying.

Around the front truck, I think the cylinder block is pretty decent, but as is often the case it needs to be shortened to accomodate the pivoting motion of the front axle. Making sure the support of the front axle (green) fit between the cylinders (blue) was also a big issue, even though the cylinders go out to 9-wide (and this would be like triply bad if I used a rigid 10-coupled section).

I think I got good mileage out of this (purple) technic joiner though:

With most of the chassis figured out, it's time to build some of the "real thing". This is mainly a sanity check to see if I've still got stupid things in the assembly (like using two 1x1 bricks where I could use a 1x2 - it happens a lot!) and to double check that everything comes in the colors I think they come in. And of course it gives me a chance to start seeing what said "real thing" will look like.

To Redimus' point I was fairly comfortable not connecting axle 3 to axle 4 at all at first, but I'd be open to re-evaluation.The flex connection has definitely crossed my mind, but it could add a lot of friction to an already large mechanism (but admittedly I've never tried). That being said, my first inclination was to extend the connecting rods toward each other, but 7 is not too different from 6. I'd have to think on this one more.

Next task is probably to find out if it's possible to fit the battery box (and that darn receiver) in the boiler.

[mikezang]

I am in China and I can't view any pictures in your post! Can you upload your pictures to eurobricks?

[Brickthus]

...

Now we can start on the detailed design. The first issue I tackled was the all-important method by which I'd connect all the axles that weren't already linked with connecting rods. To that end, I had known I would probably use a mechanism I had already used multiple times in the past, but I spent a lot of time trying to make it more rigid and compact. I also discovered how much easier it is to compact various assemblies by going to an all-studless chassis.

...

Thought I'd have a play with this kind of mechanism. Its functions are useful for engines of all sizes.

I see you have put the pivots of the connecting cog support structure as close to the mid-point between wheels as possible.

The design of the z20 cog, with a raised central portion of teeth, means they don't slide on each other very well.

I played with moving the pivots towards the near ends of the adjacent 2-axle modules, even beyond the axle that the connecting cog meshes with.

This means there is more turning and less sliding of the connecting cog on the cog that is on the wheel axle.

I was using axles along the length of each bogie with cross blocks for the wheels.

It does make the whole mechanism taller - perhaps it can be hidden inside the boiler or be made to look like authentic steam engine parts.

From what I have so far it would permit a 4-2-4 configuration of driving wheels; with an extra feature the central 2 axle is able to turn by the mean of the 4s, which means a 2-2-2 is possible as a potential improvement on a rigid 0-6-0 that I have in this engine. At the moment it is OK on curves but struggles on the points. There is a trade because the engine is already crammed with 2 motors, bbox, IR and gearbox!

Will post a pic when I have made more progress.

Mark

[Commander Wolf]

I am in China and I can't view any pictures in your post! Can you upload your pictures to eurobricks?

Are you sure you weren't just looking when Brickshelf was down? I've been seeing it go down on and off the past few days, and I'd be surprised that it's blocked, even in China.

Thought I'd have a play with this kind of mechanism. Its functions are useful for engines of all sizes.

I see you have put the pivots of the connecting cog support structure as close to the mid-point between wheels as possible.

The design of the z20 cog, with a raised central portion of teeth, means they don't slide on each other very well.

I played with moving the pivots towards the near ends of the adjacent 2-axle modules, even beyond the axle that the connecting cog meshes with.

This means there is more turning and less sliding of the connecting cog on the cog that is on the wheel axle.

I was using axles along the length of each bogie with cross blocks for the wheels.

It does make the whole mechanism taller - perhaps it can be hidden inside the boiler or be made to look like authentic steam engine parts.

From what I have so far it would permit a 4-2-4 configuration of driving wheels; with an extra feature the central 2 axle is able to turn by the mean of the 4s, which means a 2-2-2 is possible as a potential improvement on a rigid 0-6-0 that I have in this engine. At the moment it is OK on curves but struggles on the points. There is a trade because the engine is already crammed with 2 motors, bbox, IR and gearbox!

Will post a pic when I have made more progress.

Mark

I actually first saw this thing in "Ben" Beneke's 2006 BR39, and have since implemented it twice with various modifications. In my opinion, the biggest weakness of Ben's original implementation is that the "bogies" with the pairs of drivers are held toward each other only by the friction of the #1 connector on an axle, and this can easily loosen up over time and cause the gears to fall out of sync. As you can see, my previous implementations both involved having something to reinforce that connection.

That being said, while running on fairly flat track the reinforced mechanism does do a good job keeping the axles in sync, and it's mainly when you pick up the loco and slide the bogies around that you can mess up the synchronization.

The point about the ridge on the 20-tooth double bevels preventing them from sliding against each other smoothly is interesting: now that I think about it, I would think that it would be a problem, but in practice it has not been. However, I have not actually been transmitting significant torque through these assemblies until now (because my previous models were not powered), so it remains to be seen if that will be an issue in that case.

[Commander Wolf]

Made a fair amount of progress on this model over the past few days:

Placing the battery box and receiver was more annoying than I'd have hoped. There's a lot of lengthwise room in this boiler, but the placement of the sliding-rotational joint above the front driver means that the receiver and battery box can't go right next to each other, and that there will be a lot of dead space. I tried to keep all the dead space together in order to fit cabling, etc, and initially put the battery box directly in front of the motors and the receiver all the way at the front of the boiler.

There's actually a trick here that I'm using to get wires around the battery box to the receiver: I've made the bulk of the boiler 6-wide using the curved slope tiles which are 2 plates tall - this means that on each side of the 4-wide battery box, there's 1LU of space in which I can run wires, and hopefully that will take care of that.

There's another trick here, though I'm not sure how well it will work. In jtlan's AGEIR boxcab he put a "len"s above his pf receiver such that the receiver could be recessed. I tried this in my FM H-10-44 and it work pretty well, so I'm trying a similar thing here with a 1x1 clear cylinder such that the receiver can fit within the diameter of the boiler.

With the chassis in what I thought was more or less good shape, I spent time sketching out the body of the locomotive in more detail. As you can see, the general process for me is to first find the part and placement to suggest a particular feature, and then go back and see how to support that part (if possible). The idea is to start with the ideal and then backtrack or compromise if that isn't possible.

Then did some work filling out details on the cab and making some greeble for the valve gear. You can see a close to final rendering of the cab:

Typically, I only use the drawing to determine the placement of large features, and a model to determine what to do for individual details.

It was at this point that I found some potentially showstopping flaws in the chassis while doing load testing with rubber tires. Because of the way this chassis is geared, with the motor driving the 5th driven axle and each subsequent axle then driving the axle ahead of it, the gear on the 4th driven axle tends to climb up on the gear ahead of it and derail the 4th axle if there is a lot of load.

I've temporarily solved the issue by making the sliding rotational joint not loading bearing and redistributing that weight right between the 4th and 3rd axles, but there's going to be some balance between the derailing force and the weight of the locomotive that I'm not sure will balance out.

That being said, here's a clip of the current chassis pulling some heavy stuff:

[rahziel]

Keep "fighting" to the goal, good technics, I'll be watching this post closely, and btw great choice on the locomotive

[LEGO Train 12 Volts]

It's awesome to see the right colors for this epic project ...and see this beauty comes to light is fantastic!

[THERIZE]

Very cool! Can't wait to see more!

[zephyr1934]

Then did some work filling out details on the cab and making some greeble for the valve gear. You can see a close to final rendering of the cab:

I'm liking that cab

[LEGO Train 12 Volts]

Thanks for sharing this great video!

The locomotive runs really smooth on rails!

[Commander Wolf]

Well, this project got derailed for a while because a) World of Warships open beta came out and b) I messed up.

Long story short, I read some numbers wrong, and very late in the game I found out that I was making the loco too big relative to all of my other locos - the scale was about 15% bigger. This was really annoying because things were already tight and I'd have to make a lot of compromises to shrink the loco just 15% - but after a lot of Warships and mulling over it occasionally, I acquiesced and completed what I call the 'Small QJ'.

Fundamentally, the idea is the same as the big QJ: The engines are in the body and connected to the chassis via a series of universal joints going through the pivots. This is such that I don't have huge amounts of overhang when going through turns, and it will be more stable than having the body fixed to what is effectively a very short center chassis.

The main difference is that due to the smaller scale, the chassis has to have a non-articulated BFBFB arrangement, which I consider a huge tradeoff as I really don't like the difference in apparent size between the B and F drivers and how the drivers hang off the rail... Otherwise, much of the construction, layout, and greebles are about the same as the larger iteration.

At this point, the first version of this design is more or less complete; much of the work that needs to be done is tweaking the drivetrain - there's a lot of funny business in trying to keep the weight on the drivers, especially on the axle with tires - and then just making sure the model actually builds in brick. It's probably in a state where I can start ordering parts, and looking at the inventory it might not be that many,

Hopefully won't be another 2 months before the next update. At the very least I should be done before our LUG's Christmas show -_-

[LEGO Train 12 Volts]

You've done a really nice work! This new version is better than your previous locomotive! :wub;

[Doom2099]

This is getting better and better! Thanks for sharing!

[zephyr1934]

You started out with a great design (the big QJ) and the repeated iterations just keep making it better and better. Can't wait to see the continued evolution.

[THERIZE]

the smaller version is definitely better. and even though this version is smaller it's stil massive imo!

[Brickthus]

Finally got round to taking some pictures, as far as I got with articulation experiments.

There is an axial compromise in the pivot positions, between optimising for gear engagement (no sliding) and optimising for wheel turn to keep non-flanged drivers over the rails.

More pics here

The parts on top ensure that the two pivots turn by the same amount at the same time. This allows 2-2-4 as shown here, as opposed to 4-2-4 being needed without it in order to have bogies at each end to keep the wheels on the track .

I would change some parts to stop any movement from vibrations extending travel on axles and disconnecting the cogs from one another. Since moving on 2 axles would be needed in order for this to happen, there is more resistance than on some variants.

It means 14-coupled engines should be possible, as long as they use small enough wheels for BBB wheels to fit the scale!

Mark

[someguy]

I really like the bendable drivers with rotating driver sections in the first design. It looked excellent taking those turns with all 5 flanged wheels.

Amazing final result as well. Glad you stuck with 5 driving axles.

[Commander Wolf]

... annnd here it is in the flesh!

After placing and receiving all the various bricklink orders I needed, it took another week to put the thing together and work out the first round of mechanical issues. I would say it's in a good 'beta' state now where the appearance is close to final and it'll drive forward and backward through all the Lego track geometries and pull a decent amount going forward as well.

I was pretty replused by the BFBFB driver arrangement for a long time, but it looks a bit better in brick than in LDD and probably is more accurate in the end. This wheel arrangement still tracks more poorly than the fully articulated wheel arrangement though; the wide spacing between flanged wheels (idle and driver) tends to make all wheels more prone to picking switches, and even moreso the little guide channels in the switches.

Still don't have a LiPo battery so I haven't tested the configuration where the battery box and receiver are in the loco rather than the tender, but I'm pretty confident it should work - it'll also get rid of those damn wires between the cab and tender.

I really like this tender though; almost as cool as the one on the T1.

Still on the to do list:

• Stickers for logos, etc.
  
• Fix/replace a number of greebles that are crappy/don't work
  
• Gear ratio is currently 1:1, but ideally should be more like 1:1.5/2ish; currently there's really not much torque until you get to notch 3ish.
  
• Make it not derail going backwards through s-curves while pulling/pushing something heavy
  
• Still missing various parts from window panes to lipo battery
  
• Lubricate - maybe
  
• Load test
  

[THERIZE]

Cool! But I think you need to change the cables because well, you know it. But still it looks awesome!

[legoman666]

Awesome. Any chance of getting the LDD file? Would love to make one of these.

[UrbanErwin]

Oh wow, this one looks great, for the driver problem, perhaps it is possible to paint the flanges black to make them less visible?

[Heppeng]

Wow. This is a fantastic locomotive! You may not realise it, but the gear system you used for your articulated chassis was actually used on real life steam locomotives, the 'Luttermoller' axle:

https://en.wikipedia.org/wiki/Lutterm%C3%B6ller_axle