The Atlantic has a great overview of the history of mechanical horses.
A Brief History of Mechanical Horses A Brief History of Mechanical Horses - Megan Garber - The Atlantic
Footage of GE's "Walking Truck," a four legged transport device operated by a technician inside the body. The Walking Truck climbs a stack of railroad ties, then kicks each tie off the pile. The Walking Truck gives a shove to a stuck jeep. The Walking Truck nudges a lightbulb without breaking it. [GE ca. 1965]