Operating Principle: Servos operate using an internal closed-loop feedback network consisting of a DC motor, a gear reduction train, a position-sensing potentiometer or encoder, and a built-in control circuit board. The controller compares the input pulse-width modulation (PWM) signal against the current shaft position and applies power until the error reaches zero.

• Key Characteristics: High holding torque within a fixed angular range (typically 0°–180° or 0°–270°), automatic position correction under external load, and zero need for external calibration or homing logic.
• Primary Applications:
  • Joint articulation in robotic arms (shoulders, elbows, wrists).
  • Robotic claws, end-effectors, and adaptive grippers.
  • Front-wheel steering linkages in RC cars and rovers.
  • 2-axis and 3-axis pan-tilt camera mounts and sensor stabilization gimbals.
  • Control surface actuation in RC aircraft (ailerons, elevators, rudders).

Operating Principle: Steppers use an open-loop architecture with multiple electromagnetic coils arranged around a central rotor. By energizing specific phase coils in a precise sequence, the motor rotates in fixed angular steps (commonly 1.8° per step, yielding 200 full steps per revolution). Advanced micro-stepping drivers further subdivide these steps into fractionally smaller movements.

• Key Characteristics: Precise 360-degree multi-turn rotation without cumulative position drift, high holding torque at zero RPM, and full position repeatability. They consume continuous holding current even when stationary to maintain their position.
• Primary Applications:
  • Axis drives and filament extruders in 3D printers (FDM/SLA).
  • X-Y-Z axis positioning in desktop CNC routers, laser engravers, and plotters.
  • Automated camera sliders and time-lapse rigs.
  • Automated liquid dispensing, syringe pumps, and precision laboratory equipment.
  • High-precision rotary indexing tables and automated dials.

Operating Principle: BO motors pair a low-cost, high-RPM brushed DC core with an integrated plastic gear reduction box (typically 1:48 or 1:120 gear ratio) housed in a lightweight plastic casing.

• Key Characteristics: Low cost, lightweight construction, double-flat (D-shaft) or cross-shaft output designed for direct press-fit plastic wheels, and standard operation on low-voltage DC (3V to 12V). They provide continuous rotation without native position feedback.
• Primary Applications: Entry-level 2WD and 4WD mobile robot chassis, basic line-following platforms, STEM education kits, simple DIY conveyor belts.

Operating Principle: These motors integrate a brushed or brushless DC motor with an attached spur gear head. The mechanical gear reduction lowers the output shaft RPM while proportionally increasing available torque (Torque × Speed = Power).

• Key Characteristics: Metal gear construction for higher wear resistance, wide range of fixed gear ratios, standard center-shaft or offset-shaft form factors, and smooth continuous speed control using PWM signals via external motor drivers (H-bridges).
• Primary Applications: Medium-duty mobile platforms, service rovers, winch assemblies, hoisting rigs, industrial model conveyors, automated door actuators.

Operating Principle: Planetary gearboxes arrange multiple outer "planet" gears around a central "sun" gear, all contained within an internal tooth ring gear. As the sun gear spins, it drives all planet gears simultaneously, distributing the mechanical load across multiple contact points.

• Key Characteristics: Superior torque density, high energy efficiency (~90%–97% per stage), slim cylindrical inline shaft design, high resistance to shock loads, and minimal mechanical backlash.
• Primary Applications: Heavy Autonomous Guided Vehicles (AGVs), ROS-based mapping rovers, automated solar panel cleaning robots, pipe-inspection crawlers, exoskeleton joints.

Operating Principle: N20 motors house an ultra-compact DC core paired with an open micro metal spur gearbox within a standardized sub-miniature frame (12mm × 10mm).

• Key Characteristics: High torque-to-size ratio, durable all-metal gearing, low weight (~10g–15g), 3mm D-shaft output, and optional rear-shaft magnetic quadrature encoders for closed-loop control.
• Primary Applications: Micromouse maze-solving robots, high-speed mini line-followers, mini-sumo combat robots, miniature robotic end-effectors, smart door locks.

Operating Principle: Johnson motors utilize a heavy-duty 18,000 RPM DC base motor paired with a 37mm diameter off-centered (side-shaft) metal spur gearbox.

• Key Characteristics: Massive stall torque (up to 30–80 kg·cm), 6mm hardened steel side shaft with metal bushings, high current draw under load (requiring high-amp drivers like BTS7960 or Cytron MD10C), and rugged shock resistance.
• Primary Applications: Combat robots (RoboWars), heavy-duty 4WD/6WD all-terrain mobile chassis, industrial gate openers, heavy cable winches.