This post is a reference for the different types of gears that might be relevant for robotics applications.
Change Gearing Ratio
SpurA cylindrical gear with straight teeth that run parallel to the axis of rotation.
A cylindrical gear with angled teeth that form a helix shape around the gear.
A helical gear. Like a spur gear but capable of handling higher torques.
Internal Gear
PlanetaryA gear system in which multiple gears rotate around a central sun gear to transmit power and torque.
A harmonic drive is a type of gear system that uses an elliptical flexure to transfer motion between a wave generator and a flexible cup. It offers high gear ratios, high accuracy, and zero backlash, making it useful in applications where precision is important. The gearing ratio for a harmonic drive can be expressed as For example, a gear with 50 outer teeth and 52 inner teeth would have a gearing ratio of r = E / (C - E) where E is the number of teeth on the (outer) circular ring gear and C is the number of teeth on the (inner) elliptical gear.50 / (52 - 50) = 50 / 2 = 25.
A cycloidal drive uses an eccentrically mounted cycloidal disc to transfer motion between a input shaft and a rotating output shaft. It offers high torque capacity and low noise, making it useful in industrial machinery. The gearing ratio for a cycloidal drive can be expressed as For example, a gear with 10 outer pins and 9 inner pins would have a gearing ratio of r = L / (P - L) where P is the number of (outer) ring pins and L is the number of (inner) roller pins.9 / (10 - 9) = 9.
Two coaxial gears glued together. Simple enough to reason about.
Change Direction
BevelA gear with angled teeth that intersect at a point and used to transfer motion between non-parallel shafts.
Right Angle
WormA gear with a screw-like shape that meshes with a helical gear and is used to transfer motion at a right angle. These are usually used for high torque applications because they have a big gearing ratio.
A type of bevel gear that is designed to transfer power between two shafts that are at a right angle to each other.
A bevel gear with non-intersecting axes and an offset between the shafts.
Rotational to Linear
Rack and PinionA gear in which a flat bar (the rack) meshes with a gear (the pinion) to convert rotational motion into linear motion.
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