Modular Marble Decade Counter?

I want to build a unique mechanical counter and I’ve come across an interesting design challenge.


There are marble “clocks” that count up the time – typically in a rack of single-minute balls, a rack of 5-minute balls, and a rack of hour balls.
When the last ball reaches a rack, it dumps out all the balls and sends a single ball to the next rack.

I’m thinking this concept would be great for a mechanical decade counter – just have one rack per digit of what you’re counting.


Type A:

Type B:


With chimes, strange lifting mechanisms, or “complex just because”

Most of these clocks are like type A – they use racks with a “deer scarer” tipping mechanism – when enough balls land in the rack, they all tip out.

Some like type B use a better alternative – the last ball bounces out and releases a gate that allows all the stored balls to roll through the rack.

Why not follow these designs?

All the existing designs have a common flaw; balls flow from top to bottom, the least significant rack is at the top. To read the state of the display you have to unintuitively read the racks from bottom to top.

This seems a bit ‘wrong’ to me. Naturally you read numbers from left to right.
An ideal mechanism would:

  • Have racks arranged horizontally with the least significant digit on the right.
  • Have each rack store the balls vertically to increase density.

I want to design a 100% modular “digit” of such a mechanism, so I can stack as many of them horizontally as needed.

Horizontal, ball enters from the right, currently showing “1 4 2 3”.

The Challenge:

Conservation of energy.
If the design is like the above picture, where the rail is flat…

  • As the ball rolls it will slow down.
  • Each rack the ball rolls past needs to be emptied by some mechanical trigger – which will absorb speed.

When a rack is emptied, surely those 9 balls that fall out could be harnessed to transfer energy back to the rolling ball?

The devil being in the details, what would you suggest for the design of this “digit”?

  1. Must hold 0-9 balls in a visible way.
  2. Each new ball enters horizontally from the right with some initial velocity.
    (eg from the ball lifter mechanism)
  3. Balls #1-#9 need to be captured.
  4. Ball #10 needs to empty the digit, AND
  5. Ball #10 (or another ball if you’re fancy) needs to exit horizontally to the left at the same height it entered and at the same speed.

Watch this space…