Leonardo da Vinci’s self-propelled cart design used three wheels.
The cart was a spring-powered vehicle described in Leonardo’s notebooks from the late 15th or early 16th century. Two large driving wheels supported the main body, while a smaller front wheel helped steer the vehicle. Coiled springs stored energy and released it through a system of gears.
Because the cart could move without being pushed or pulled by an animal, it is often described as an early ancestor of the automobile or a programmable mechanical device. The exact purpose is uncertain. Some historians have suggested theatrical use, such as making a ceremonial figure move during a performance.
Leonardo did not leave a complete modern engineering manual for the machine, so reconstructions have helped test how it may have worked. The cart is sometimes called a robot, although it was not a robot in the modern electronic sense. It had no computer, sensors, or feedback system.