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…

How To: Solder Battery Tabs


This article covers one method of attaching wires to a bare lithium-polymer battery pouch. This could also be done using a battery spot welder, clamping, or screwing.

Warning: Lithium Ion and Lithium Polymer batteries can catch on fire if shorted, punctured or overheated.
Be careful when soldering that the battery does not become hot.
Ensure you have an appropriate fire extinguisher nearby. 

Step 1: Wire Prep

Before you solder the terminals, plan your wiring.
Where should the battery wires exit the battery? In what direction will they go, and how far? (A scale printout of the layout may help)

Strip and tin the wire ends.
Each bare end should be slightly shorter than the battery tab’s width.

Step 2: Tab Prep

Peel back one of the battery terminals.

With a small file, roughen the outer half of the battery tab.

Fold the end of the battery tab over, to create a small ‘hook’.
It should be just large enough to fit the wire in.

Put a tiny drop of flux in the hook.
You can spread it around with a piece of wire.

Step 3: Soldering

Place the wire into the hook – making sure it matches the polarity – and press it closed.
It may help to clamp a little bit of the insulation in the hook as well.

Carefully, press the soldering iron against the folded hook.
The aim here is to heat up the tab, the wire and the flux, without heating up the battery.
If the battery near the tab is warm, stop and wait 2-3 minutes before attempting again.

Run the solder into the folded hook until it begins to melt and ‘wet’ to the metal.
As soon as it seems that a good contact has been made, stop. The solder should have bonded well to both sides of the hook, and to the wire as well.

Step 4: Tidying

Roll the tab up until it is inside the battery sled.
Replace the covering tape.

Repeat for the second battery tab and wire.

Step 5: Finish Up

Once both tabs are soldered, the wires can be fixed in place with hot glue, and the area covered with a small quantity of masking tape. Complete!