technique
Go motion
Stop motion
Definition
Go motion is a stop-motion variant in which a rod puppet, rigged to a motion-control system, is driven a small amount during the exposure itself -- not only repositioned between exposures -- so the moving camera shutter records genuine photographic motion blur that ordinary frame-by-frame stop motion, where the puppet holds perfectly still for every frame, cannot produce.
Overview
Phil Tippett and Jon Berg developed go motion at Industrial Light & Magic for The Empire Strikes Back (1980), animating the AT-AT walkers and tauntauns of the Battle of Hoth. Animator Brian Knep, who later worked with Tippett on the technique, describes the underlying method plainly: a puppet, its motors keyed to a motion-control rig, is posed, then "moved to the next pose and it would basically hold both poses and move between them as you open and close the shutter, giving you this nice motion blur that you didn't get in normal stop-motion." The result reads as smoother, more cinematic movement than the crisp, faintly strobing look of a puppet held dead-still for every exposure -- the visual signature by which a trained eye had long recognised stop motion as stop motion.
ILM proved the technique on a larger, more demanding subject for Dragonslayer (1981): Vermithrax Pejorative, a dragon built as sixteen separate puppets covering flying, crawling and fire-breathing action. Tippett was credited as dragon supervisor for the go-motion crawling and breathing work, with Ken Ralston separately supervising the flying puppet. The film earned an Academy Award nomination for Best Visual Effects (losing to Raiders of the Lost Ark, ILM's own other nominee that year) -- evidence that go motion had moved from a Star Wars-specific trick to a repeatable, credit-worthy production technique in its own right.
Go motion kept working through the decade -- ED-209's ponderous, blur-softened stride in RoboCop (1987) is a later credited example -- but it met its limit on Jurassic Park. Tippett and effects supervisor Craig Hayes had already planned the production around it: "basically all the full-motion dinosaurs were going to be foam, latex, aluminium and steel armature stop-motion puppets, that would then be shot on bluescreen," in Hayes's account. That plan ended the moment Steven Spielberg saw an experimental computer-animated Tyrannosaurus test alongside Tippett and effects supervisor Dennis Muren. Tippett's own summary of the moment is now one of visual-effects history's most quoted lines: told the dinosaurs would be computer-generated instead, he said, "I feel extinct." He was not removed from the production -- ILM and Tippett Studio instead built the Dinosaur Input Device, a stop-motion-style armature wired to feed an animator's hand-posed movement directly into the CG models, carrying go motion's frame-by-frame animator's touch into computer animation rather than discarding it.
The name survives in current tools for a different reason than nostalgia. Dragonframe's own Arc motion-control workspace labels its newest robotic-arm mode "go motion" -- shooting with a six-axis arm itself in continuous motion during a take (see Arc: motion control and robotic arms in Dragonframe) -- reviving Tippett and Berg's 1980 term for a digital motion-control rig rather than a hand-tuned mechanical one. No stop-motion rod puppet or bespoke armature is required to trigger it; the label has outlived the specific hardware it was coined to describe.
Workflow
- Rig the puppet's moving points -- limbs, jaw, wings -- to a motion-control system that can record and repeat a keyframed move, rather than relying on the animator's hand alone to hold a pose still.
- Pose the puppet for the current frame, then let the rig begin driving it toward the next keyframed pose.
- Trigger the exposure while the rig is mid-move between the two poses, so the puppet is not stationary when the shutter is open.
- Repeat pose-to-pose across the whole shot, checking exposures for blur that reads as directional motion rather than as a simple soft or double image.
- Reserve go motion for shots where the blur itself sells speed or scale (a striding walker, a diving creature) -- static or slow business is usually still shot as ordinary, dead-still stop motion, since the motion-control rig and its setup time cost more than a standard rig.