Spur gears, worm drives, linkages, cams, and the drivetrains that make robots move.
Animated spur gears meshing at a 2:1 ratio — the driven gear has twice the teeth of the driver.
Four-Bar Linkage
Mechanisms convert input motion into desired output through rigid bodies and joints -- bridging motors to robot actions.
Gears transmit rotary motion between shafts. The gear ratio determines the speed-torque trade-off.
Gear Ratio = Driven Teeth / Driver Teeth
Example: A 60-tooth driven gear meshed with a 20-tooth driver gear → 60 / 20 = 3:1 ratio. The output shaft turns 3× slower but with 3× the torque.
Straight teeth parallel to the axis. Ideal for parallel shafts. Easy to manufacture but noisy at high speeds.
Cone-shaped gears for intersecting shafts, typically at 90°. Used to change drive direction. Common in differentials.
A worm meshes with a wheel for very high ratios in compact space. Naturally self-locking, ideal for lifts and winches.
Sun, planet, and ring gears in a compact coaxial arrangement. High torque density with multiple ratios. Common in servo gearboxes.
Beyond gears, robots use these mechanisms to convert and redirect motion.
Four bars connected by revolute joints in a closed loop. Varying link lengths yields crank-rocker, double-crank, or double-rocker motion. Used in arms, claws, and walking legs.
Converts rotary to linear motion (or vice versa) via a crank and connecting rod. Used in piston actuators and punching mechanisms.
A profiled cam pushes a follower along a precise path. Motion profile (rise, dwell, return) is set by cam shape. Useful for timing and indexing.
Transmits motion between distant shafts. Timing belts prevent slippage (3D printers, linear stages). V-belts absorb shock. Ratio works like gears: larger driven pulley = more torque, less speed.
The drivetrain determines how a mobile robot moves, trading off maneuverability, speed, complexity, and traction.
Two independently driven sides. Turns via speed differential. Simple, durable, strong push. Skid-steering wears wheels on hard surfaces.
Angled rollers enable omnidirectional movement without rotating the chassis. Complex control but unmatched agility.
Each wheel steers and drives independently. Tank power meets mecanum agility. Most complex but the gold standard in competition.
Two driven wheels on a common axis with casters for balance. The simplest drivetrain. Common in educational robots and AGVs.
Model gears as simplified cylinders with pitch-circle diameters for assembly work. Full tooth profiles are only needed for manufacturing drawings or FEA.
Cam & Follower Mechanism — a rotating cam with harmonic profile drives a flat-face follower through its guide.
If you double the number of teeth on the driven gear, what happens to the output speed?
Gear Ratio = Driven Teeth / Driver Teeth
Ratio > 1: torque multiplication (slower, stronger). Ratio < 1: speed multiplication (faster, weaker).
Power is conserved (minus friction): Torque x Speed = constant
Common ratios in robotics: 3:1 to 100:1 for arms, 1:1 to 5:1 for drivetrains.
Your competition robot needs to launch a ball. Design the mechanism approach.