Star Wars' cutest droids would get stuck on the beach | Science News for Students

Star Wars' cutest droids would get stuck on the beach

The wheels on a droid go round and round, until that droid rolls into sand
May 4, 2018 — 6:30 am EST
star wars droids

R2D2 (left) and BB-8 (right) appear to roll right across desert sand. But in reality they’d be left spinning their wheels. 

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R2D2 and BB-8 never seem to let anything hold them back, even when faced with vast, terrifying desert planets. R2D2 trundles cheerfully across the sands of Tatooine. BB-8 takes his own sandy trek on Jakku. Sadly, such scenarios aren’t realistic. Not because Star Wars is fiction (though it is). It’s because a droid with wheels has no place on a desert planet.

“Wheels don’t work well in sand, period,” says Robin Murphy. She studies robotics at Texas A&M University in College Station. Wheels, she notes, “dig in. The traction is just not there.” Using them in a setting on sand, she says, is just “wrong on so many levels.” Murphy published an article on the pros and cons of Star Wars droids February 21 in the journal Science Robotics

It’s easy to think that the wheels of R2D2 or the ball of BB-8 would just slip over the sand. But slipping is why they would be in trouble. It has to do with the way a wheel rolls, explains Daniel Goldman. He studies biophysics — the physical forces related to living things — at the Georgia Institute of Technology in Atlanta.

Sandy surfaces

A wheel (or a BB unit) moves forward because there is no slipping between the wheel and the ground. “If an ant was riding on a wheel, it would go around, contact the ground and come up at the same point,” notes Goldman. This is because there is friction — resistance that the wheel encounters as it comes in contact with the ground.

That works pretty well inside the Millennium Falcon, with its solid metal floors. But sand is different. It’s not a solid surface but a compilation of tiny particles of rock. Those small pieces slip and move against one another. If BB-8 attempted to roll across a dune, the sand would slip around the little droid. The robot would soon dig itself into a hole. And as the little ball kept spinning, the sand would continue to slip. BB-8 would be unable to get enough friction under itself to climb out.

Goldman knows just how badly this turns out. “We tried it, when [Star Wars: Episode VII The Force Awakens] came out,” he says. Goldman and his colleagues placed a model of BB-8 on a bed of sand. “It’s terrible,” he explains. “It makes a little pit it can’t climb out of.”

R2D2 wouldn’t be much more successful, notes Murphy. The older droid (which made its first appearance in 1977’s Star Wars: Episode IV A New Hope) has sets of wheels on its “feet” that would get just as stuck.

When dealing with slippery substances like sand, Murphy explains, it’s best to have lots of surface area in contact with the surface. “When you see things going across the desert, they use the properties of the sand like sidewinders,” she notes. Sidewinders are a type of snake. They don’t press into the sand as they move. Instead, they flatten their bodies, which helps them keep contact with the sand.

A sidewinder-like robot might be one option for a desert droid. Another might be a droid that uses wide, flat treads to move, like a tank. Those treads spread out the tank’s weight and prevent the vehicle from sinking in as it moves.

Murphy and Goldman have mused about droids because they are developing robots that can handle any terrain. Such robots would be useful for tasks ranging from search and rescue after a disaster to exploring distant worlds in space. So, while BB-8 and R2D2 belong in a galaxy long ago and far away, the lessons they provide could be pretty useful to us Earthlings here and now.  

Director J.J. Abrams of Star Wars: The Force Awakens and others discuss how the idea for the BB-8 droid came about — and more.
Star Wars: The Force Awakens/YouTube

Technically Fiction is a blog that finds the science in the realm of the fantastic. Have a comment or a suggestion for a future post? Send an email to

Power Words

(more about Power Words)

biophysics     The study of physical forces as they relate to living things. People who work in this field are known as biophysicists.

colleague     Someone who works with another; a co-worker or team member.

droid   A fictional robot with artificial intelligence. The term was coined for use in the Star Wars universe, and is short for android.

fiction     (adj. fictional) An idea or a story that is made-up, not a depiction of real events.

force     Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

friction     The resistance that one surface or object encounters when moving over or through another material (such as a fluid or a gas). Friction generally causes a heating, which can damage a surface of some material as it rubs against another.

galaxy     A massive group of stars bound together by gravity. Galaxies, which each typically include between 10 million and 100 trillion stars, also include clouds of gas, dust and the remnants of exploded stars.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject.

model     A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.

physical     (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood.

resistance      (in physics) Something that keeps a physical material (such as a block of wood, flow of water or air) from moving freely, usually because it provides friction to impede its motion.

robot     A machine that can sense its environment, process information and respond with specific actions. Some robots can act without any human input, while others are guided by a human.

scenario     A possible (or likely) sequence of events and how they might play out.

science fiction     A field of literary or filmed stories that take place against a backdrop of fantasy, usually based on speculations about how science and engineering will direct developments in the distant future. The plots in many of these stories focus on space travel, exaggerated changes attributed to evolution or life in (or on) alien worlds.

surface area     The area of some material’s surface. In general, smaller materials and ones with rougher or more convoluted surfaces have a greater exterior surface area — per unit mass — than larger items or ones with smoother exteriors. That becomes important when chemical, biological or physical processes occur on a surface.

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

terrain     The land in a particular area and whatever covers it. The term might refer to anything from a smooth, flat and dry landscape to a mountainous region covered with boulders, bogs and forest cover.