Modular Mechanical Calculator

This mechanical calculator automatically carries addition and subtraction operations.  The long mark on the read gear indicates the number that each digit is displaying.

To add (e.g.) 43+19, you would first move the 1's gear to 3 and the 10's gear to 4.  Then move the 1's gear forward by 9 places (the 1 will automatically carry to the 10's gear), then move the 10's gear forward by 1 place.  Subtraction works similarly, but you move the gears backwards.  Multiply and divide by repeated addition and subtraction, as you would on an abacus.

This design is expandable to many digits.  Carrying through multiple digits (e.g. 99+1 = 100) is possible, but takes more force.  Presumably at some point with many digits this force will exceed the tolerance of plastic parts.

For info on how I designed this model, see this blog post.

PRINT INSTRUCTIONS

For 2 digits:

• 2 spacers
• 2 read gears
• 2 long pegs
• 2 dials
• 1 carry gear (with supports)
• 1 base
• 1 short peg

For each additional digit:

• 1 read gear
• 1 long peg
• 1 dial
• 1 carry gear (with supports)
• 1 base
• 1 short peg

ASSEMBLY PICTURES

Base & spacers

Full assembly. Green pegs on gears with arms are short, blue on gears with notches are long. Pegs slot through holes in the corners of the frame, then rotate into place.

Side View

Gear and base frame positions alternate between high and low for each successive digit.
 

(Yellow print is an older version of the model, red is the current version.  Both were on an Ender 3 in PLA, 20% infill)