Gears
Toothed wheels that mesh to transmit rotational motion and torque.
Key principle: Both gears have the same linear (tangential) speed at the mesh point.
Gear ratio = teeth on driven gear / teeth on driver gear
- Small driver → large driven: driven turns slower, but produces more torque (torque multiplication).
- Large driver → small driven: driven turns faster, but less torque (speed increase).
- Meshing gears always rotate in opposite directions. Add an idler gear to maintain the same direction.
Example: Driver = 40 teeth, driven = 10 teeth. Gear ratio = 10/40 = 1/4. Driven spins 4× faster with 1/4 the torque.
Bevel gears: Conical shape; transmit rotation between perpendicular (non-parallel) shafts (e.g., car differential).
Worm gear: A screw-shaped driver meshing with a helical gear. Very high gear reduction. Self-locking — the gear cannot back-drive the worm.