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kbricks construction system

by robkern Apr 19, 2019
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Thanks for the updates. Would it be possible for you to maintain a changelog csv or xls file on the parts as an additional thing file? Perhaps a log that lists the part file name, a description of the part, last update and an update log that tracks by date any changes made? This will make it easier for folks to track than through this comment section as this section will grow.

Please note that all changes are summarized in the change history section at the bottom of the Thing Details page. The master change history is tracked on GitHub where you can see exactly how the scad sources and the stl files have developed over time. My plan is not to remove any parts but only add new ones or improve existing ones in a way that they are still compatible with the other parts.

kbricks construction system
by robkern

Just added a couple of new parts that will be used by the upcoming kbricks truck: A corner cube (cube_corner), two-sided plates that can be used from both sides, locked beams to be used as crank levers, a disk plate, worm gears, a stronger cardan joint (cardan_joint_thick) and some other parts. Stay tuned...

@rob, what would be great would be a super simple toy for which you could make one stl file containing all the necessary parts, all aligned the right way. Call it a Starter Kit. Just enough to get people up and running in no time. Get 'em hooked, then go from there. Just an idea :).

@John, I really like the idea of a starter kit! How about having two STL files, one for a few silver parts and one for a few yellow parts, along with some simple examples what you could build from these parts? (Should be really simple models that just consist of a couple of parts.)

I just published my first make of this. It is a remix with a modified peg, and connectors that allow "mini" 2:3 scale models.


KBricks -- quad and mini quad

This is a really intriguing system. I'm playing with it and with user TKRoth's train derivative. It will probably take me a while to print and assemble enough to make intelligent comments. However, I offer a big think you for posting the source files on Github so that derivatives can be truly compatible.

I have one question though. Have you considered a KBricks-mini? At 2/3 size the basic modulus would be 16x16 or 2x2 Lego studs. That way it would be very easy to make Lego adapter blocks to add Lego structures to a KBricks creation. if that makes the connectors too small, maybe they could be scaled up a little in relation to the base parts. This would also be considerably faster to print.

Also a thought. How about creating a KBricks group here on Thingiverse (or elsewhere) so that comments and questions could be shared separate from specific model comment threads?

Thanks for your feedback! I have seen your kbricks mini model and I really like it! The little Lego man and his car are looking very cute. Did you also try to print small axles and gears? I was afraid that they would become too fragile and too hard to handle. That's why I made the kbricks cubes 24 mm which would btw. still allow for creating a Lego adapter because 24 = 3 * 8 = size of three Lego studs.

I also like the idea of a kbricks group here on Thingiverse and I created one right away: https://www.thingiverse.com/groups/kbricks

Thanks for the reply. I'm glad you like my efforts. I'm a model railroader, and for the past couple of weeks my hobby time has been primarily going into preparing for an upcoming show. So I haven't played much more with the basic KBricks system.

However, I do have a couple of derivative projects in the works:

1) a car base and negative reserved space piece so that you can cut car models to put the base into them. This is inspired by the Duplo car craze and particularly https://www.thingiverse.com/thing:3220777 which provides a similar cut for creating Duplo cars.

2) some rethinking of 'TKRoth's' train system. Needlepoint axle for low friction (practical powered train??), end beam with separate coupler pocket to allow design of more reasonable coupler, and some other ideas.

Land Rover & How To Create Lego Duplo Car

I'm having trouble getting the pegs to fit. They are just a little too wide for the holes. I tried making the ends a little thinner, but part of the problem is that with PLA they break pretty easily. Any tips? Maybe I just need to give them a bit more attention with the dremel tool.

Did you try to smoothen the pegs and the space between their wings using an abrasive paper? I usually press together the wings with my fingers a few times in order to make them more flexible. It is important that there is no support material between the wings.

Working on a Nerf tactical rail mount that takes kbricks. https://www.thingiverse.com/thing:3646440

Nerf rail kbrick adaptor

So cool, I love this idea!

Several people have asked for a kbricks motor mount or motor case. It has indeed been my hope from the beginning that the community would come up with cases and mounts for all kinds of electrical or electronic devices like motors, switches, buttons, batteries, microcontrollers, sensors, LEDs, etc.

I have created a first prototype of a motor case for a small DC motor shown on the attached pictures. The motor is hidden in a case of the size of two kbricks cubes. Cables may be laid inside the notches of the kbricks parts, even underneath the slide connectors (this is one of the reasons why the connectors are concave). So when wiring a kbricks model, ideally all cables will be hidden in its notches and you won't see any of them from the outside.

The prototype works well but I am not happy with the male motor shaft because it will be difficult to replace when it breaks. I therefore plan to replace it by a female shaft so axles of different lengths can be connected to it.

This is really sweet. My grandson will love it. Question: Can you disassemble the blocks to make something else, or is it best to just print components for another model?

Thanks for sharing. I love toys that inspire kids to be creative!

You can easily disassemble and reassemble, though I suggest to print a few extra connectors when printing with PLA. I'm printing 25 a pop and it's done in about an hour.

I was asked whether kbricks is compatible to fischertechnik and indeed, the kbricks slide connectors are inspired by and compatible to the ones of the fischertechnik construction system. However, the brick sizes differ: The kbricks cube size is 24 mm while the basic fischertechnik brick is 30 mm x 15 mm x 15 mm.

As you can see on the attached pictures, a kbricks cube (24 mm) plus a kbricks plate (6 mm) still add up to the 30 mm of the fischertechnik brick.

I'm printing this on on a more-or-less stock Anet A8. I did run into some issues which I believe are caused by the printer more than the model:
Printing the connectors "lying flat" is impossible. With and without retraction, the model is too brittle to even peel off the glass print bed. Printing them "upright" works great, though, as no retraction or travelling is necessary.
When printing with PLA from BQ, the connectors do. not. fit. Try as I might, I would need considerable force (say, a hammer) to get them into the cubes. After a bit of trying, I increased the size of the cubes by five percent (scaling them to 105% in Cura) while keeping the connectors at 100%. That way, they slide into the slots nicely without falling through, they work as expected.
I'm currently printing a few connectors using flexible TPU filament to see if that helps with unscaled cubes.
Scaling down the connectors to 95% did not work. At that size, with a .4 nozzle, the walls would get reduced to just one wall, resulting in considerably weaker connectors that break apart at the slightest pull.

I'll let you know how well the TPU connectors hold up.

Okay, after being an idiot and not watching the video to the end, I now actually drilled the 4mm holes which leads to the PLA connectors sliding into position much easier.

I did try an TPU connector anyway, and there's a point to them: They are a little less strong in keeping the cubes together (ie: less force required to pull cubes apart), but in testing here a few PLA connectors broke apart in the process. The TPU connectors are still in good shape after pulling two cubes apart about 20 times.


Thanks for the update on TPU! I never tried that because I was afraid that the connections may become too flexible (and because I didn't have TPU at hand).

If any adjustments should be required I would strongly recommend to resize the connectors rather than the other bricks in order to keep the other bricks compatible to those printed on other printers. The OpenSCAD source is available on GitHub. By setting the value of the connector_tolerance constant to 0.1 or so the connectors will become slightly smaller and easier to insert. With the slot constant inside the connector module you can adjust the thickness of the connector.

How well would this work with a .6 nozzle? Even if I do have to swap nozzles this still seems like a cool project.

I am using the default 0.4 mm nozzle of the Prusa i3 MK3. Not sure whether 0.6 mm will work as well. Maybe it's worth trying.

Nice project ! I will give it a try !

Very cool set!
I love the idea. I don't know when I'll get to print these and try them out with my favorite great nephew, but it will happen!

I honestly hope you're in/going to design school. This could be a major school project. It's very, very impressive.

Thanks, Rick! I am glad you like it! I am actually not in a design school but I spent a lot of time on playing with Lego Technic and other construction systems in my younger day ;-)

Man, this is cool! Printing!

Am I missing something with cube_1hole_open.stl though? I don't see any built-in support there?

Thanks again - kids and I will love this!

Hi Tobias,
good catch! For some reason the embedded support was indeed missing for part cube_1hole_open.stl which is surprising because the OpenSCAD source (managed on GitHub) had been correct. I just updated the part here and also for the tractor and the forklift. Thank you for pointing me to this issue!

Btw., I am glad that you like kbricks and I am curious to see what you will build from it. Please let me know if you have any recommendations for improvement!

kbricks tractor
by robkern
kbricks forklift
by robkern

Hi Robert,

will let you know! Thanks for the quick reply!

Thank you for the great work on this project :) I realy like this idea of an open source construction system.

I am using cura 4.x and can´t find the entry for "detect thin walls". Could you descripe where i could find this entry ?


Thanks for the positive feedback! "Detect thin walls" is an option of the Slic3r slicer software. Please compare your slicer preview to the following image to see whether your slicer is configured correctly. The horizontal slots of the parts must be closed by a thin wall. This applies to all kbricks parts with horizontal slots (typically all parts with "cube" or "seat" in their names). If the thin walls are missing, the slots won't be printed correctly because of overhanging structures.

Slicer preview with and without embedded support

In cura you can find the setting "Print Thin Wall" under Shell (see attached screenshoot)
Hope that helps some new cura users.

Thanks for that. I was thinking I'd have to download Slic3r just to have a go at this print.

This is really cool! Are the beams/pegs/axles compatible with LEGO Technic? How are the connectors between the cubes meant to be removed?

Thanks! The beams/pegs/axles are bigger than in LEGO Technic in order to make them stronger. The snap rings also work differently so they cannot move. However, you could easily design a LEGO interface because the kbricks cube size is a multiple of the LEGO brick size.

In order to remove the slide connectors between the cubes you can either pull them out using a needle-nosed pliers or push them out using a hex key.

I like the apparent stability displayed once you add the multiple clips, compared to some other systems. Can you please post a video demonstrating how hard it is to break any two pieces apart once fully supported or how much flex there is in a straight chain of blocks compared to a cohesive print of the same collective profile?

Thanks for your feedback! I liked the idea of measuring the strength of the slide connectors so I have created the following video for you: https://youtu.be/r5TO2mwobMY

When designing the bricks, I experimented a lot with different types of slide connectors, e.g. prismatic vs. cylindric, solid vs. concave, thick vs. thin. Even if it is not the strongest one, the current type turned out to have a number of advantages compared to others: (1) Because it is concave, it can be pulled out using a needle-nosed pliers, (2) it leaves space to hide cables when using the bricks in combination with electronic devices, (3) it provides some elasticity, (4) it provides a predetermined breaking point so the other parts of the model will stay intact when the model breaks.

If the connectors should be too weak for certain applications, one could still experiment with different materials (in the video I am using PLA with a 0.15mm layer height), print them vertically rather that horizontally, or make the connectors slightly thicker by adjusting the corresponding parameter in the OpenSCAD source (see http://kbricks.org). Also, chains of multiple cubes could be provided out of the box.

Thank you very much for the video and the quick response, Rob. I see that the connector breaks at 14 kg of pressure but the assembly begins to bow well before that. Assuming the standard 24 mm x 20% infill cubes, at what length does a 'chain' of KBrick blocks begin to bow on its own and how much?

I apologize for my late reply, Sean! For spanning longer distances I would rather recommend to use a cross beam construction than a basic chain of cubes. Maybe something like the one displayed on the attached picture.

I love this, you could build this I-beam even stronger with 4x1x1 multi-cubes and peg connectors that span across two cubes to help anchor them together and spread loads.