Reverse Engineering Challenge- in the spirit of RailBricks

[zephyr1934]

Back in the days of RailBricks, I had a column, "Reverse Engineering Challenge" that would present the result of a clever building technique for Lego train builders and challenge the reader to figure out how it was done. 
I am not building as much as I would like these days, but I will occasionally still come up with a clever trick or two. Last year I built this flat car for a static display my club put on. I was aiming for something that might have appeared in a Bill Peet book (e.g., the Caboose Who Got Loose). 

As built, the six logs just stacked on the car, which was fine for the static display. But I also wanted to be able to run the car hassle free, in other words, attach the logs so that they would not roll around or slide off. When viewed from the end, I wanted the logs to look like a clean stack in an equilateral triangle shape. 

 

As I quickly discovered (and am now sharing with you), building 60° angles in Lego can be a challenge. It took me quite some time, but I finally got it working in the past few weeks.

This was handy enough I figured I'll share the joy and see if you can come up with some way of stacking six logs in this same equilateral triangle shape such that they are connected without looking too much like they are connected. There's no one right way to do it, but I'd enjoy seeing what you come up with. Please post your solution to this thread. Do not be inhibited if someone else comes up with a different solution or even the same solution as you did, share your work regardless. There is no prize beyond any meager glory this thread might offer.

 

[Stereo]

This is my first thought for how to make it happen that seems workable, though it leaves that one 1x1 round plate fairly visible.  The geometry's about 0.025 studs overlapping so I don't know if the round bricks have enough built in side tolerance to allow it.  I don't own any 5518s to test it.  Third layer would have this repeat but pointing downwards to attach the middle 4 in a diamond, the outer 2 of the bottom layer can just be built into the deck the same way the middle is, probably.

Instead of using all the quarter tiles, the old-style 2x2 round tiles can connect directly onto the half-circle jumpers, but I haven't checked if those have a wood print.

Edited June 16 by Stereo

[zephyr1934]

  On 6/16/2025 at 2:06 AM, Stereo said:

This is my first thought for how to make it happen that seems workable, though it leaves that one 1x1 round plate fairly visible.  The geometry's about 0.025 studs overlapping so I don't know if the round bricks have enough built in side tolerance to allow it.  I don't own any 5518s to test it.  Third layer would have this repeat but pointing downwards to attach the middle 4 in a diamond, the outer 2 of the bottom layer can just be built into the deck the same way the middle is, probably.

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Oh, that's nice. If the geometry works that would be a slick solution. Then if you add the third 2x2 round brick on the bottom, to the left of your current assembly you are on to something. Remember that except at the ends, the bottom middle log is unseen so it gives you a small amount of space to hide your work. The round tiles in the middle of the logs will give you strength problems though. If you replace the 1x1 round plate with a 1x1 round brick you can do away with the tiles and it will be a lot stronger.

[Stereo]

Yeah, I'd probably have 2 of these near the ends with the axles connecting the middle sections where the studs reverse, so there's not much "overhang" past the layer that uses tiles.

[L-Gauger]

Hello all! 

This is my first post to EuroBricks, so forgive me if the photos don't work properly this first time, still figuring things out. However, after a few tries I have a solution for this Reverse-Engineering Challenge. In my solution, each layer of logs is connected to the others by 1x2 plates with round ends, and the bottom layer of logs is connected by a 1x4 plate. I'm still finding the best combination of plates and tiles to better hide the connections, but the prototype I presently have is surprisingly stable, and mostly hides the fact that the logs are connected together. Please excuse the random brick colors, as that is the nature of prototyping...

Edited June 20 by L-Gauger

[zephyr1934]

  On 6/18/2025 at 7:12 PM, L-Gauger said:

after a few tries I have a solution for this Reverse-Engineering Challenge. In my solution, each layer of logs is connected to the others by 1x2 plates with round ends, and the bottom layer of logs is connected by a 1x4 plate. I'm still finding the best combination of plates and tiles to better hide the connections, but the prototype I presently have is surprisingly stable, and mostly hides the fact that the logs are connected together. Please excuse the random brick colors, as that is the nature of prototyping...

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This sounds interesting. Unfortunately the pictures did not come through. For Eurobricks you need to post the photos on a different host (e.g., flickr) and link to them from your EB post.

[L-Gauger]

Sorry about that, @zephyr1934! I'm working on that, hopefully the photos will be up and working within the next few days. 

EDIT: I think I got it figured out... the photos from my first post should be visible now, and here are two more: 

This is the less-perfect side of my prototype at the moment, but I think I have a way to get rid of the 1x1 round plates. I just have to find where I put my half-round 1x2 "jumper" plates. 

And here's a view from below. As you can see, it is necessary for the bottom middle log to use two 1x2 bricks. 

Edited June 20 by L-Gauger

[zephyr1934]

  On 6/18/2025 at 7:12 PM, L-Gauger said:

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Oh, that's clever! The one weakness I can see are the tiles, but like Stereo's solution, if they are near the end of the logs they shouldn't be an issue.

It is neat to see the different solution paths, especially since they are so different. I would say we are two for two in terms of working solutions, or really three for three since mine took a different approach. I'll hold off with my reveal for a little while to see if any other solutions come in.

 

[Stereo]

Another sturdy one, that has colour problems:

6558 3L Technic pins are blue/black(/tan/lbg)

17485 2x2 round brick with pinholes are dark orange/dark brown/tan/black(/blue/lbg).

18674 2x2 round jumpers are reddish brown/dark tan/black(/blue/lbg).

 

I suppose if you want to stack pipes instead of logs, you could go LBG, Blue or Black.  Or a mix.  I would probably build 2 of these facing opposite ways, to connect with axles in the usual fashion for stud inversion.

Edited June 22 by Stereo

[L-Gauger]

  On 6/22/2025 at 3:51 PM, zephyr1934 said:

Oh, that's clever! The one weakness I can see are the tiles, but like Stereo's solution, if they are near the end of the logs they shouldn't be an issue.

It is neat to see the different solution paths, especially since they are so different. I would say we are two for two in terms of working solutions, or really three for three since mine took a different approach. I'll hold off with my reveal for a little while to see if any other solutions come in.

 

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Thank you! Because I built my prototype in real life, I decided to do a little strength testing. It will hold up to usual handling but not to being dropped on the floor. 

As you noted though, keeping the weaker joints near the ends of the logs makes a big improvement for strength. 

I wonder if there's a way to modify my design and make the 1x2 plates with rounded ends look like straps holding the logs down? That would permit the use of Dark Bluish Gray or Black 1x2 plates with rounded ends instead of the harder-to-come-by Reddish Brown ones. 

[zephyr1934]

  On 6/22/2025 at 5:05 PM, Stereo said:

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Very nice, I wanted to use those bricks with pin holes to hold the top log on, but they are not (yet) available in brown.

Had the part been available I would have used 1x1 round plates to fill the exposed pin holes. I had not thought about using the the plates (tiles?) with one stud to do the rotation, very resourceful.

 

  On 6/23/2025 at 10:20 PM, L-Gauger said:

I wonder if there's a way to modify my design and make the 1x2 plates with rounded ends look like straps holding the logs down? That would permit the use of Dark Bluish Gray or Black 1x2 plates with rounded ends instead of the harder-to-come-by Reddish Brown ones. 

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I contemplated doing just that, but I could not come up with anything that looked acceptable from all angles. Doesn't mean it is impossible though, if you come up with something that would make the build a lot simpler.

[zephyr1934]

I finally had time to put together my solution. My approach is way over-engineered compared to the others. I solved the problem in two parts. First, the lower 5 logs and second, the top log.

 

The middle band of the figure shows the solution to the 5 logs. I realized that when staked, the center of any two adjacent logs should be exactly two studs apart, so the bottom row centers could all be connected with a 5 long technic beam, and the middle row centers could be connected by a 3 long technic beam. Meanwhile, if I connected the end logs on the two rows, that would also force them to be adjacent. The relatively new 1x2 half cylinders would allow me to hide the technic beams. Trouble is, how to hold the end logs, here the solution was a 1x2 tile, but a normal 1x2 tile would completely block the hole in the 2x2 round bricks needed to connect to the technic beams. Ah, 1x2 tile with rounded ends would allow me to get a bar through. That pretty much solved the bottom 5 logs, I did this assembly on either end.

 

For the top log I had a couple of solutions that worked with varying levels of success. The one I finally went with is shown on the right band. The top log holds a 1x2 jumper plate that is forced between a pair of 1x2 half cylinders. I can't quite tell, there might be a little stress in this assembly, but it is close enough that it works.

[Selander]

Thanks for sharing your challenge. It's been fun following the thread 👍🙌🤗