What Leonardo da Vinci invention was a three-wheeled cart that could move without a person pushing it?

Leonardo da Vinci's self-propelled cart was a three-wheeled vehicle designed to move without a person pushing it. Leonardo sketched it around 1478–1480, making it one of his earliest known designs for an autonomous machine.

The cart used coiled springs inside its two large rear drums as a source of stored energy. When the springs unwound, gears transferred their motion to the wheels. A programmable steering system, using blocks on a drum, could set the cart to follow a chosen path.

Historians debate the cart's exact purpose. It may have been intended as a theatrical stage device, perhaps for Renaissance court celebrations, rather than as a practical road vehicle. Leonardo did not leave a complete written explanation of its operation.

Modern reconstructions have shown that the design can work, although builders have had to interpret missing details and adjust the mechanism. It is therefore best described as a mechanical concept, not a mass-produced automobile.