# Spur gear

> Component kind `spur-gear` (category `mech`, DSL name `spurGear`, API v1)

Cylindrical gear with straight teeth. The canonical mechanical building block: mates with other spur gears of the same module via `mech.mesh`.

## Parameters

- **`module`** — Tooth module (mm per tooth). Two meshing gears must share the same module.
- **`teeth`** — Tooth count. Must be ≥ 4. Pitch radius = module × teeth / 2.
- **`width`** — Face width along the spin axis (mm).
- **`boreDiameter`** — Central bore diameter (mm), for mounting on a shaft.
- **`pressureAngle`** — Tooth pressure angle (deg). Standard is 20°.

## Parameters schema

| Parameter | Type | Default | Constraints |
| --- | --- | --- | --- |
| `module` | Number | 2 |  |
| `teeth` | Number | 20 | min: 4 |
| `width` | Number | 10 |  |
| `boreDiameter` | Number | 8 |  |
| `pressureAngle` | Number | 20 |  |
| `color` | String | — |  |

## Ports

| Port | Type | Description |
| --- | --- | --- |
| `axis` | `rotational` | Spin axis (rotational). Receives ω from the coupling or mesh propagation. |

## Kinematics

Mesh rule: ω_driven = -ω_driver · (teeth_driver / teeth_driven). Sign flips because meshed gears spin opposite ways.

## Example

```
spurGear "G1" {
  teeth: 20
  module: 2
  at: position(0, 0, 0)
}
```