Computer-generated lightsabers, laser blasts, and aliens may have filled the Star Wars prequels, but the original trilogy featured some stunning practical effects that still stand up today. On YouTube, Star Wars has posted an old behind-the-scenes video of how the filmmakers made one of the series' most impressive effects: the AT-ATs moving at the Battle of Hoth. The video shows time-lapse footage of animators adjusting large AT-AT models frame-by-frame, while Industrial Light & Magic effects artist Dennis Muren explains how they planned out the shoot.

"Sometimes we'd get a shot a day, if we were doing real good."

Before settling on stop-motion animation, Muren says that the effects team actually considered creating a five-foot-tall, robotic AT-AT that could actually move, but that the idea was scrapped because it sounded too expensive and complicated. Instead, they choose to do frame-by-frame stop motion with models that were "about as big as a person can animate" — a limit defined by how well a person can get their hands around a model to move it. Choosing stop-motion was by no means a compromise though: Muren says the intention was to use the staccato look of stop-motion animation to help emulate how such a large machine might actually move.

The rest of the setup is deceptively simple. Baking soda was used as Hoth's snow, while a large painting was stood behind the AT-ATs to act as the backdrop. After that, it was a matter of the animators slowly moving the models and taking a photograph 24 times for every second of footage they needed. With each shot lasting around five seconds, Muren says, "Sometimes we'd get a shot a day, if we were doing real good." Complicated and time consuming as it may be, the results were likely worth it for how convincing they come off. Of course, even though stop-motion animation has fallen out of style, ILM is still creating some of today's most amazing blockbuster effects through other means.