Build a Mechanical Lego Binary Calculator




I decided to take the time to design this as a Christmas gift for my stepmother, who is a math teacher.  That would be why it is Christmas colored.  After a day or three of hours put into designing it (and the case), I find out that Lego doesn't let you order your designs from their digital designer program anymore.  So I count each piece by type and color (too much time invested to give up), and then go to order the parts through Lego's "Pick A Brick" program.  The price was well over $1,000 which was not affordable for a jobless recent HS graduate.  I checked 3d printing services about their prices to have the parts 3d printed, and I think it was an even higher cost due to their greediness.  I'm sure it can be printed for under $100 easily, but I do not have a 3D printer sadly :/
Hopefully someone who has a 3D printer or a LOT of specific Legos, will find this instructable useful and save my time/efforts from being in vein :)  A thing to take into thought before spending money on this:  This hasn't been tested and I imagine all of the tolerance limitations legos have may cause it to not work.  This is a concept design. 

I didn't really want any springs, and hate when rubber bands are used in machines for long term use, so I designed it to work off gravity and it has to be standing up in order to work.

I didn't think of the entire thing, I just got the idea after learning how computers add numbers, and based the logic gate designs off of this guy's gates.

Please point out typos and mistakes i've made.  Kinda made this quickly.

Step 1: How Does It Work?

The calculator is designed to work off of mechanical logic gates, meaning it works similar to a computer.  Through networking different types of logic gates together, you can create more advanced logic gates.  Let's look at the designs of the three logic gates that make up this calculator.

Keep in mind, these all can likely be simplified, and I am 100% sure some of them can be compacted into smaller versions.  Feel free to alter the design.

if you do not understand logic gates, I recommend watching this video.  This is the video that I learned from and got the idea for this from.

Based on this video, we will need AND, OR, and XOR logic gates.

Step 2: The OR Gate

This is the simplest gate.  It's pretty simple, push any of the two input pins down, and the output pin goes down.

To download the designs and see how to put them together with instructions:
Download Lego Digital Designer
Download my design files by clicking on this link, and then searching in the username field "hifatpeople"

Step 3:

The AND gate is where things start needing thought.  

Step 4: The XOR Gate

Each of these inputs/ouput are attatched to a lever end, and weighted to return to the off position unless being acted upon.  Other than that, it's simply another OR gate.

Step 5: The Half Adder

Following the diagram in step one, we can combine 2 XOR gates, 2 AND gates, and one OR gate to make a half adder.

I have files for every step on my lego page (the easiest place i could find to upload these files for sharing)

The labels I have on here are wrong,  I actually don't remember what parts are what here.

Step 6: Full Adder

This is made by combining two half adders with each other.  Connect the carry out of the first half, to an input of the 2nd half.

This picture contains a carry over bar, to carry digits over to the next full adder.  You'll notice little white pegs too.  this is so that the extension adders (additional full adders) can attach to the frame.

Step 7: The Completed and Wired 10 Digit Binary Calculator

The rest is up to you, you'll have to wire each adder together however you want.  

The 10 digit adder file actually crashes the digital designer program due to bad program writing.  I built my computer for about $1,000.  It has a 4GHz 8 core processor, 32GB RAM, a gpu capable of games on ultra, and is run on an SSD.  The program crashes when developing building instructions for this file while the processor and RAM are not used very much at all.  That is why I make this instructable step by step by breaking it down into it's components.  

It is tricky wiring it all together and you have to take into consideration that plastic flexes.

If you want the rest of the files, send me a message.  I have 3D files for some parts if you have a 3D printer, and a parts list.



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    8 Discussions


    Reply 4 months ago

    Hi Mr Darker, firstly I am a big fan of your work. I was wondering if there are other files for this project because none of the links here work. I want to use it for part of a computer I am making.


    Reply 4 months ago

    Hi Mr_Darker, Two quick questions: One, is it alright if i use this design for a mechanical cpu? Two, the link for the files doesn't work, are there any files elsewhere for this design. I love your work.


    5 months ago

    Wow, only 5 years ago, feels like i was in kindergarden when I wrote this.


    5 years ago

    I looked on ebay for each individual part actually. Found many good deals but was still over 200 which is more than i could afford


    5 years ago

    The lego parts are cheaper via 3D printing, but the printing services I tried had a huge service fee, at which point I quit because christmas was a few days away.

    Injection molding isn't really practical for my needs because I only want one. And if it were to be 3D printed or injection molded, I'd probably redesign it in Autocad to get rid of the design limitations and bulk that comes with lego designs.

    Though I may just do that. I don't really know why people would fund a calculator thats not for them, and I'd probably get sued by LEGO if I tried to sell this. But it might be something to consider if i redesign it.

    I'll go scavenge through the lego bin and see if I have enough parts for a gate.


    5 years ago on Introduction

    It looks great and I would love to see a full version of it working at some point.

    I'm pretty sure that Lego parts will be cheaper than 3D printed parts. The injection moulding process is more expensive to set up but cheaper and faster once it's running. 3D printing all those parts will be slow which is why there is such a markup.

    Would it be possible to make on of each gate you're proposing, the videos would really help people see what's going on here. Once you had that done I reckon you could head to kickstarter and people would soon give you the money you need for a full version.


    5 years ago on Introduction

    Looks like you made that with LEGO Digital Designer? If so, you should look for LDDManager which can make a complete part list from LDD file that you can then copy to Bricklink site. Bricklink is like the ultimate Pick A Brick, with millions parts from many various sellers. You can probably get everything you need to build one for about half of what LEGO wants.