In the special effects business, any mechanism that operates using a 1:1 movement ratio rather than using conventional input devices (levers, switches, knobs, etc.) or preprogrammed movement sequences. Waldo devices are often used for filming
complicated live-action sequences, such as smoothly
controlling a humanoid or lifelike
animatronics system, making a radio-controlled full-size vehicle act exactly as if there was a real driver behind the wheel in a stunt sequence, etc. Simply put, they are used when intuitive controls are needed above all else.
The
Mythbusters used a Waldo rig to make a bus roll itself over in their
Demolition Derby Special.
Doc Ock's tentacles in
Spider-Man 2 were controlled by a miniature Waldo setup. Where the controllers put the tentacles in the model, they moved behind the actor.