"Interstellar" director Christopher Nolan is a big proponent of making his movies look as real as possible.

In “The Dark Knight Rises” he actually had a plane dropped from the sky to film the movie’s opening scene. A revolving set was used to create an elaborate fight scene in “Inception.”

So it shouldn't come as a big surprise that in his latest movie, the film's two monolith-like robots TARS and CASE had hardly any digital effects.

Several puppets weighing 200 pounds were constructed and filmed alongside cast members. TARS voice actor and comedian Bill Irwin actually lugged them around set. Digital effects were brought in later for a few select scenes and to clean up any instances of Irwin in the film.

Actor Bill Irwin on set of "Interstellar" manning TARS with Matthew McConaughey and Nolan. Paramount Back in November, during the film's release, Business Insider spoke with both special effects coordinator, Scott Fisher, and visual effects supervisor, Paul Franklin in separate interviews to find out how TARS came together.

Since "Interstellar" is out on Blu-Ray and DVD Tuesday, we wanted to share this story again with new imagery.

"Chris [Nolan] started talking about TARS very early on in pre-production," says Franklin. "And I said, ‘Well, what is this robot going to look like?’ And he said, ‘Well, I don’t want it to be a sort of conventional idea of what a robot should be in science fiction. He didn’t want to make it look like just a mechanical mat ... which is typically what happens with robots in science fiction films. They tend to be sort of machine analogs of a human being. At the same time, he wanted the thing to have a real level of physical reality to it."

Franklin's team at visual effects studio Double Negative spent a lot of time figuring out how TARS may run, fold his arms, and do various other movements.

At the same time, Scott Fisher's practical effects team set out to configure a giant puppet for Irwin to haul around. Fisher says TARS didn't undergo many different looks.

Production designer Nathan Crowley explains in "Interstellar: Beyond Time and Space" that a lot of inspiration for the robots came from balsa wood and lollipop sticks.

"We started working with the original designs that Nathan had and as far as the size and the shape and seeing what we could do with a person behind it, working it," explained Fisher. "We ended up with several different puppets that we could use that he [Irwin] moved around the set and was able to interact with the actors on set and … I think that’s what makes it kind of neat."

"Bill would actually be able to operate this thing and he was essentially effectively sort of shackled to the back of it," said Franklin.

The design team ended up creating four puppets on set which consisted of TARS and CASE and their own backup robots. Each was tasked with performing different movements.

"We had one that was in the ship that could raise its head," explains Fisher. "We had one that would come out of the back of the ship. We had another one that had more intricate arm movement where the arm could fold out and then a few digits could fold out from that. We had two real hero walkers."

Here's the version of TARS that could raise its head aboard the spaceship Endurance. Paramount/Interstellar trailer The main challenge was nailing down TARS's movements on screen, something which Irwin helped the crew figure out.

"There’s a lot of trial and error as we built him to see what Bill could do and what he could handle and on different surfaces," tells Fisher. "In Iceland we had to walk through ... it was almost two feet of water. Each one [surface] kind of had a different challenge. Some were kind of slippery. It was hard to move on those. He [Irwin] just had to figure out what was the right kind of tool for each situation."

Fisher says TARS ended up with three different walks in total.

"There’s what we call the “ape walk” and then there’s a “crutch walk” where the two outside legs and the center spins through," he said. "And then there’s where all three legs move independently."

Here you can see TARS performing his two-legged walk. Paramount/Interstellar

After filming with a practical puppet of TARS, the visual effects team made minor edits which included taking out some wires, physical props and rigs, and wiping out any instances of Irwin in the film.

"We would erase Bill if we saw him because obviously he’s a little bit taller than TARS," said Franklin. "But then we would add things like … if TARS’ arm might fold out and a smaller finer arm might come out at the end. We would add that digitally."

Digital effects were also used to add an extra wow factor to the robots for when they were moving through water and flying through the sky on other planets.

"Mostly, our digital work was confined to those moments where TARS and CASE, his twin robot, tend to do extraordinary things like turn into the waterwheel and move through the water to be able to collect Dr. Brand, pick her up, and run with her," Franklin explained.

Fisher and the practical effects team built physical rigs that allowed the visual effects team to correctly interpret the robots' interactions with the water.

"He had a sort of water wheel rig attached to a quad-bike which we could drive through the water to create all the splashing," said Franklin. "And, then we would add the digital robots into this shot. We’d raise the quad-bike and we’d have a digital robot driving the splashes."

"That produced this very extraordinary result where you believe he’s real because most of the time you’re looking at reality," he added. "When he’s running across the ice, for example, that’s a digital robot. But when he climbs up inside the spacecraft, he’s real."

Fisher noted how unusual it was for a director to take this approach to both TARS and CASE.

"I think most film directors would look at that character and instantly think CG but he [Nolan] instantly thought let’s do as much practical as we can. Let’s see what kind of a puppet we can build," said Fisher. "That's a classic kind of a Nolan thing right there."

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