---
title: "Geneva Drive Interactive Lab | Sandbox Physics"
description: "One turn in. One step out. Then wait. How can a turning input make the output wait?"
canonical_url: "https://sandboxphysics.com/labs/geneva-drive/"
language: "en"
page_type: "lab"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/labs/geneva-drive/"
last_modified: "2026-10-20"
---

Mechanism design · Intermittent motion

# Geneva Drive

Watch a gold pin enter an open radial slot, index the output wheel and leave it at rest. Change the slot count, scrub through engagement and measure how much of each driver turn is spent waiting.

> Interactive simulation: open this page in a web browser to change the parameters and run the model.

Ideal external Geneva kinematics with a schematic controlled brake holding the dwell. The traditional locking arcs are omitted. Prescribed input speed; no impact, inertia, friction, backlash or brake-force model.

Physics tutorial

## Design the pause into the motion

**Background** A pin can transmit motion through a slot without a connecting rod.

**Why it matters** The apparatus and the quantitative record share the same exact geometric state.

Start with the essentials

- **Focus question**: How can a continuously turning input produce a stationary output?
- **One-sentence intuition**: Only the pin-engaged interval produces an index. An independent holding constraint is essential during the remaining dwell.

### Core mathematical model

#### Tangent entry geometry

$$
\alpha=\frac{\pi}{n},\qquad r=d\sin\alpha,\qquad\beta=\frac{\pi}{2}-\alpha
$$

The pin engages while the crank angle lies between the negative and positive engagement half-angle.

#### Output index during engagement

$$
\phi=-\alpha-\operatorname{atan2}(r\sin\theta,d-r\cos\theta)
$$

Output angle is zero at entry and decreases by one slot pitch at exit. The wheel is held fixed during dwell.

#### Dwell and index

$$
\Delta\phi=-\frac{2\pi}{n},\qquad f_{\rm dwell}=\frac12+\frac1n
$$

These fractions assume one driver pin and uniform prescribed input speed.

#### Quasistatic drive torque

$$
\tau_{\rm in}=-\tau_o\frac{\mathrm d\phi}{\mathrm d\theta}
$$

During dwell the ideal holding brake balances the external output torque, with no input-pin power transfer.

### Common difficulties

#### Prescribed motion

**Typical misconception** A smooth-looking animation proves smooth forces.

**Better mental model** Input speed is imposed. Dynamic inertia, impacts, friction and flexibility are omitted. Geneva boundary acceleration is discontinuous.

#### Signed load

**Typical misconception** A constant external load must always resist motion.

**Better mental model** A constant signed force or torque can supply or absorb power depending on output velocity.

### Run the experiment

1. 01

   #### Follow the pin

   Play one turn, then scrub the cycle or drag the gold pin in the plan.

   **What to observe:** The input pin, output and graph cursors move together.

2. 02

   #### Change the slot count

   Compare four, six and eight slots at the same input speed.

   **What to observe:** More slots make smaller steps and a smaller fraction of the driver turn is spent dwelling.

3. 03

   #### Check the boundary

   Use Pin entry and Pin exit, then inspect the dwell brake. Export the cycle.

   **What to observe:** Boundary acceleration is undefined; the disengaged slot residual is unavailable rather than a fictitious contact check.

Physical conclusion

Kinematics specifies the motion; it does not establish contact forces or a real motor’s ability to produce it.

Theory & apparatus: [Carnegie Mellon · Geneva Wheel](https://www.cs.cmu.edu/~rapidproto/mechanisms/chpt8.html) · [Purdue · Scotch Yoke](https://www.physics.purdue.edu/demos/display_page.php?item=1S-30)

Motion & dynamics · Starter path

## From a falling ball to an orbit

Measure gravity, split motion into components, add contact forces and collisions, then carry the same laws into orbit.

[Start here → **Free Fall & Measuring Gravity** Capture a few drops and fit the camera positions to estimate gravitational acceleration. Then add air damping and watch the fit drift from the truth. Observe · 14 min](https://sandboxphysics.com/labs/free-fall/)

1. [1 Free Fall & Measuring Gravity](https://sandboxphysics.com/labs/free-fall/)
2. [2 Projectile Flight Designer](https://sandboxphysics.com/labs/projectile-flight/)
3. [3 Inclined Plane & Friction](https://sandboxphysics.com/labs/inclined-plane/)
4. [4 One-Dimensional Collision Bench](https://sandboxphysics.com/labs/collision-bench/)
5. [5 Mass–Spring Oscillator](https://sandboxphysics.com/labs/mass-spring/)
6. [6 How Orbits Take Shape](https://sandboxphysics.com/labs/orbit/)

[View the full path →](https://sandboxphysics.com/topics/mechanics/#starter-path)