# Geneva Mechanism & Variants

How a Geneva drive turns a steady spin into quarter\-turn steps with rests between, including six\-slot, two\-pin and internal versions\.

By merry\-comet\-a700e135

Topic: Machines

[Open the interactive Jig](https://ask.jig.com/j/iL0xdyenGUHg)

## Transcript

### 1. A wheel that pauses

This machine turns a steady spin into neat stop\-and\-go steps\. The round driver never stops, yet the cross\-shaped wheel beside it jumps a quarter turn, waits, then jumps again\. It is called a Geneva drive\. Drag anywhere around the machines to look around\.

Old film projectors used it to pull film one frame at a time, 24 frames every second\.

### 2. Two partners

The glowing parts on the driver are a single round pin and a raised locking disc\. The wheel has four slots, which give it the shape people call a Maltese cross\. The pin does the pushing and the disc does the holding\.

### 3. One push, one quarter turn

Watch in slow motion\. The pin slides straight into a slot, sweeps the wheel round by 90 degrees and slides out again\. Because it enters along the slot, it starts the wheel gently instead of hitting it\.

Four slots means 360 divided by 4: a quarter turn for every turn of the driver\.

### 4. Locked while it rests

Between pushes, the curved edge of the locking disc sits snugly in a matching curve on the wheel\. Now the wheel cannot drift or wobble\. With four slots, it rests for three quarters of every driver turn\.

The driver turns 90 degrees while the wheel moves, and 270 degrees while it rests\.

### 5. Your turn: crank it

Press on the round driver and drag it around in a circle\. Turn it slowly and feel the rhythm: long rest, quick step, long rest\. Try turning it backwards too\.

You can grab the driver of whichever machine you are looking at in the next steps as well\.

### 6. More slots, smaller steps

This wheel has six slots, so each push turns it 60 degrees, a sixth of a circle\. It rests for two thirds of every driver turn\. More slots give smaller, gentler steps\.

Wheels usually have between 3 and 18 slots\.

### 7. Two pins, twice the steps

Give the driver a second pin and the wheel steps twice for every driver turn\. The locking disc gets a second cutaway so each pin has room to work\. The rests become shorter, so the wheel moves more of the time\.

### 8. Inside out

In the internal Geneva drive, the slots face inward on a ring and the pin works inside it\. Now the ring turns the same way as the driver, and it is moving for three quarters of each turn\. The ride is smoother, but the machine is bigger\.

In the outside version the wheel always turns the opposite way to the driver\.

### 9. The Geneva stop

One slot of this wheel is filled in\. After four driver turns the pin meets the solid edge and the driver is blocked\. Watchmakers once used this trick to stop a spring from being wound too tight\.

The same idea still turns tool changers, bottle fillers and even the filter wheel on the Dawn space probe camera\.