In an interview with Star Wars Universe, robot designer Tony Dyson (who created the R2-D2 units for “The Empire Strikes Back”) talked about the biggest challenge when working with R2 — the robot’s third leg.
“The overall design of R2 tends to be a little unstable, due to the fact that the legs are connected to the highest part of the body,” Dyson said. “Therefore, when the third leg extends, the whole unit has to be restrained from moving forward.” Dyson explained that the third leg is pushed down by electronic activators and that the foot has a drive wheel that moves the leg forward when in contact with the ground, which in turn twists the body until it reaches its stopping point. “When it locks off, this forms a tripod configuration and should also allow the droid to drive on rough ground and even mount stairs,” he said. “That’s the theory anyway.”
R2 was not the only droid that caused problems for its designers, or its actors. Just like Kenny Baker had a very uncomfortable time in his two roles in the “Star Wars” movies, “The Empire Strikes Back” caused Anthony Daniels plenty of discomfort while playing C-3PO. During the scene in the Millennium Falcon where C-3PO was still being put back together, Daniels had to stand on one leg while wearing the full suit.