A planetary gear system consists of multiple gears that work together to transmit torque and speed. It typically includes a central gear called the sun gear, surrounded by one or more planet gears that rotate around it. These planet gears are mounted on a movable arm known as the planet carrier, which can also rotate. This arrangement allows for compact design and efficient power transfer. The outermost gear, known as the ring gear, encircles the planet gears and meshes with them. Planetary gear systems are commonly used in applications like automatic transmissions in vehicles and robotics, where they provide high torque in a small space while allowing for various gear ratios.