How to Make a Working Mechanical Lego Calculator

This Instructable will show you how to make a functioning lego calculator that can add +,subtract -,multiply x, and divide \! It uses a gear train that turns one rotation of the control knob into a tenth of a rotation on the tens dial. By engaging, rotating to numbers, and disengaging the control knob in patterns you can do basic arithmetic. Thank you and enjoy!!

Step 1: Make Base and Frame

You can place the two supports anywhere on the base as long as you keep the supports two studs apart. It depends on how tall your paper indicator is.

Step 2: Gear Assemblies

The first gear assembly is the control knob's: there should be space between the gear and the two 4x1 technic bricks so the gear can slide back and forth. This makes it so you can toggle the engagement of the gear. The second assembly is just a 1:1 transfer and the ones place output. The third assembly is the first step in the tens place output.

Step 3: Attach the Gears

Make sure you can pull and push the control knob's axle: this is VERY IMPORTANT.

Step 4: Another Gear and a Spacer

Step 5: Last Gears

This is the gear assembly for the tens dial: this gear will pop out if you turn it too fast.

Step 6: Indicator and Dials

This is where you make your own indicator! You can use my paper to help you make your own but the design depends on your version.

Step 7: How to Use Your Calculator

This will show you use the calculator you just built: To add, you turn the control knob counterclockwise to the first number you add, then you pull out the control knob, reset to 0, and turn the knob counterclockwise to the next number you add: your answer will be on the tens and ones indicators. To subtract you reset to 0, then you disengage the control knob, go to the number you want to be subtracted, disengage, go to the number you want to subtract, engage, then turn clockwise to 0. Multiplying is just adding the same number over and over again, while dividing is subtracting the same number over and over again. Thank you for reading this and have fun with your new calculator!