Space, Physics, and Math

How Do Motion-Sensing Video Game Controllers Work?

--asks Zak from Cleveland, Ohio

December 18, 2006
The Power Glove was somewhat of a disappointment for those seeking more physical interaction with their videogames. [CREDIT: Wikipedia]
The Power Glove was somewhat of a disappointment for those seeking more physical interaction with their videogames. [CREDIT: Wikipedia]

Seasoned video game players used to laugh when beginners waved the controller up in the air, urging Mario to jump a little further, but now these frantic motions have become part of the game.

The new Nintendo Wii and Sony Playstation 3 gaming systems, just released for the holidays, both include motion-sensing controllers. Nintendo, in particular, has used its motion-sensing controller as the primary selling point of the Wii. But how are the controllers able to precisely and accurately measure physical movement?

At the heart of the controller technology are tiny accelerometers. Inside these chips, silicon springs anchor a silicon wafer to the rigid controller. As you wave the controller through the air at an attacking enemy, the wafer presses onto the springs, just as you are pressed against the seat of a car when you stomp on the gas pedal. The faster the controller accelerates, the more the wafer moves relative to the rest of the chip.

The accelerometer monitors the position of the wafer by measuring capacitance, or the ability to store electric charge, in different directions. When you move the controller forward in a punch, the capacitance increases at the back of the wafer and decreases at the front. Using capacitance to measure how far and in what direction the wafer moves, the system translates your real-life movements into the perfect jab to your opponent’s face.

Accelerometers were bulky and expensive when they were first used to guide real-life missiles and aircraft, but they became available for gaming when engineers began producing them the same way computer chips are made.

The accelerometers used in the Nintendo controller are thinner than a penny, small enough to fit twelve on a postage stamp, and sell for under $6 a piece. They can accurately measure forces more than three times stronger than the pull of gravity in three directions – up and down, side to side, and forward and back. The chips also use gravity to determine the orientation of the controller, whether you’re holding it vertically like a golf club or horizontally like a gun.

But accelerometers alone cannot provide complete control, because small positional errors add up over time, like when you need to re-center your mouse on a mousepad.

Nintendo addressed this problem by including a sensor bar that can be placed above or below the television. Each end of the bar emits a beam of infrared light like a television remote, which is monitored by a sensor on the controller that works like a digital camera: by seeing where the two spots of light fall on its grid of more than 750,000 pixels, the sensor can determine where the controller is pointing and translate it to a position on the television screen.

Even by combining technologies, game developers have yet to maximize the ability of motion sensing. The Wii ignores some of the motion sensing data it collects and simplifies the gameplay to compensate for different living rooms and players. In his Slate magazine review of the Wii, Erik Sofge, complained that a table-tennis flick of the wrist was just as effective as a proper baseball swing.

As gamers demand improved realism and accuracy in their video games, engineers will continue to push towards better motion-sensing technologies, and likely use more sensor combinations. But if you need to swing a real baseball bat right now your best bet is to go to the park.

About the Author

Joshua J Romero

Josh comes to science writing in New York City after studying astronomy and physics in Arizona. While he misses never wearing real shoes, Josh relishes the opportunity to read about science, politics, arts and culture on his daily subway rides. A former college-radio DJ, he is often found late at night in a half-empty, downtown bar listening to a noisy, experimental band with no record deal. He is fascinated with the boundaries of science, where it must intersect with politics, art, religion, or human nature.



Adam Hyland says:

CNN did a pretty detailed writeup of the motion sensing features in the Wii and PS3 but failed to note how the console makers fixed the reference problem or how they simplified motions in order to achieve verisimilitude rather than outright realism. I think the two articles combined give a fairly complete picture of the issue.


I forgot all about the Power Glove! What a hideous looking contraption that thing was.

Karen says:

Did the gun for Duck Hunt work in a similar way? I always wondered that because there was definitely not an infrared sensor on the original Nintendo…

Nick says:

From ‘NES Zapper’ on Wikipedia:

“When the trigger was pulled, the game blanked out the screen with a black background for one frame, then, for one additional frame, drew a solid white rectangle around the sprite the user was supposed to be shooting at. The photodiode at the back of the Zapper would detect these changes in intensity and send a signal to the NES to indicate whether it was over a lit pixel or not. A drop followed by a spike in intensity signaled a hit. Multiple sprites were supported by flashing a solid white rectangle around each potential sprite, one per frame.”

Karen says:

Thanks, Nick! You have finally satisfied my lifelong curiosity about the gun for Duck Hunt (a.k.a. the NES Zapper… who knew that was its real name?). And thanks to Josh for creating a forum where my inane questions can be answered by do-gooder strangers. Boy, I sure love Scienceline!

pyro says:

So does the Wii game. Do the same thing.

Amanda says:

agreed it so does satisfie my need for gaming info. (*snicker*)

Dick Samples says:

Ran on to the fact that accelorometers are now being used to detect laptops being dropped and shut down to save the drive before it hits the ground. Being 75 years old and always a curious fellow, this just blows me away!!! As have many recent inventions/applications/etc. I have been lucky to grab hold of the technological train before it completely passed me by! :-)

Luis says:

Thanks, this really helped! I’m actually doing this for a science fair project :P

Tara says:

this site is way helpful i need this info for my physics project! :)

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