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The Mechanics of Motion Sensing

Dr. Eggman writes, "The AP has a short technology piece on the mechanics that go into the motion-sensing capabilities of the Wii and PS3 controllers. It also details some of the past uses of the technology and gives a nice overview of just how far the technology has come from the earliest missile-guidance sensor equipment."

28 of 119 comments (clear)

  1. Interesting. by Mendak+Jemuna · · Score: 4, Interesting

    Interesting, but I have one question. Do the silicon springs recalibrate every so often, or will they wear out and break? My old N64 controller did this.

    1. Re:Interesting. by drinkypoo · · Score: 5, Informative

      They're so minute and move so little you will never have to worry about them breaking. Because they are so tiny you can never build up appreciable inertia in them. They are functionally considered solid state devices and they should last pretty much forever.

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    2. Re:Interesting. by indigest · · Score: 2, Informative

      "Silicon spring" is misleading because it implies there are moving parts within the accelerometer that can break. In actuality, the proof mass is held perfectly still using a feedback loop to cancel the externally applied force. The magnitude of this applied force is read out as the acceleration. No calibration is ever needed thanks to the feedback loop.

    3. Re:Interesting. by Plutonite · · Score: 2, Informative

      It is not held perfectly still in both piezoresistive and capacitive accelerometers. You need to have displacements to measure the acceleration, and stiction is the problem solved with feedback/force units.

      Or maybe I just misunderstood you..

    4. Re:Interesting. by fatphil · · Score: 5, Interesting

      Should - and do. One of Freescale Semiconductor's clients' more popular uses for accelerometers is in industrial applications -- BIG kit -- on things that vibrate constantly. Things that vibrate more and more as bearings dry or wear (hence the need for the accelerometer - so you can perform detect this and perform maintenance before your printing press, or whatever, self-destructs). The accelerometers outlive any of the parts they are supposed to look after.

      Freescale has some pretty cool electonmicrographs of their 2-axis and 3-axis accelerometers - www.freescale.com, sensors, accelerometers, and browse around - I can't actually find the images now. I have a PPT on my work laptop, but that's no use. Grab a ZSTAR for <$50, and simply have a play with one yourself - (that includes everything - hardware and development kit).

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    5. Re:Interesting. by naoursla · · Score: 4, Interesting

      I asked a MEMS researched about this once. He said it comes down to fatigue. If you bend a paperclip back and forth a bunch of times the metal fatigues and eventually breaks. Fatigue occurs because the metal actually migrates around the bend. MEMS components are so small and move so quickly that they do not rest in one position long enough for fatigue to occur. The same principle hold for the springs in accellerometers and the mirrors in DMD projectors.

    6. Re:Interesting. by EmbeddedJanitor · · Score: 3, Informative

      Most accelerometers can survive 3000G or so.

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  2. Other applications by inKubus · · Score: 3, Interesting

    It would be cool to incorporate this type of controller into a portable device. You could have portable laser-tag like games with real-time mapping, or incorporate some type of ball and it automatically keeps score and records the game. You could have "operations" players indoors that have some different role (view the maps, for instance, and direct the players)

    With networking and GIS in a portable device, it's almost necessary to have new interfaces to use all the new space it knows about. In gaming it's the most fun but these types of thing could be used in more professional ways also.

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    1. Re:Other applications by MankyD · · Score: 3, Insightful
      It would be cool to incorporate this type of controller into a portable device. You could have portable laser-tag like games with real-time mapping
      While it would definitely be cool, you can't really use accelerometers as location devices. Accelerometers and, to a lesser degree, odometers both do a pretty terrible job of keeping track of where an object is located. That's why the Wii also includes a sensor bar.

      They'll generally give you pretty good readings for a single movement, like 'the object just moved 1 meter forwards', however as soon as you turn or travel a long distance, they suffer from drifting, skidding, and general measurement errors.

      A different sort of tech would be needed for mapping. You can do some research into Robotics, such Markov Localization, for some more information. GPS and related techs are better for real time location reporting.
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    2. Re:Other applications by dcam · · Score: 3, Informative
      They'll generally give you pretty good readings for a single movement, like 'the object just moved 1 meter forwards', however as soon as you turn or travel a long distance, they suffer from drifting, skidding, and general measurement errors.


      That's true of odometers, but again with accelerometers it's just a matter of engineering your system properly. (The USAF equips its fighters with inertial navigation systems - and they remain accurate through a bloody dogfight!.)


      No the OP was right. It is also true of accelerometers. And the fact that they are measuring data during a dog fight it irrelevant, it is the amount of time/distance they are measuring data. They include a random walk error that is small for a short time/distance, but compounds over time.

      You will find that typically this is corrected with something that can give an absolute position (eg GPS). Your absolute positioning device typically also has a know error. The values from both of these are generally married using a Kalman Filter or Extented Kalmna Filter.

      I've written code to do this in the past.

      I suggest that you do some research on inertial navigation and inertial guidance - because what you say is true at the level of the casual gamer, its not true (as you imply) of accelerometers in general.


      I suggest that you also do some. 4 years of Mechatronic Engineering would be good start.
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  3. The "snare" was the first motion-activated weapon? by xxxJonBoyxxx · · Score: 2, Funny

    I thought the "snare" was the first motion-activated weapon. Or was it the "covered pit"?

  4. Re:I Thought... by twistedsymphony · · Score: 4, Interesting

    In all seriousness I believe Nintendo would actually allow it. They really haven't blocked non-family content since the ESRB has been around and people have been able to get a better idea of the game content before they buy it through it's rating. Also have you seen the number of dating sims available for the DS that deal with "touching" not just in Japan but in the US too.

    The biggest roadblock to "adult" Wii entertainment isn't Nintendo but retailers, your EBGames, BestBuys, and Walmarts refuse to carry any "AO" rated titles meaning if a company did release them they'd get very limited to almost non-existent exposure... in the US at least (most of the rest of the world is a bit less prudish).

  5. MEMS by Mike1024 · · Score: 5, Informative

    A good picture of a two-axis accelerometer can be seen here: http://users.wpi.edu/~cfurlong/me-593Mech.html (second picture down). Sensing is usually performed by capacitive combs, structures which act as capacitors, with their capacitance varying with displacement.

    MEMS accelerometers have dropped in price in recent years because there's a big market: the automotive sector. A typical new car needs two accelerometers, one for the traction control system measuring roughly plus-or-minus 2 to 4g, and one for airbag deployment measuring more like 50g.

    Two big manufacturers are Analog Devices and ST Microelectronics, though others exist.

    The high demand of the automotive sector has driven prices right down; sensors which would have cost hundreds of dollars in the past can now be purchased in bulk for less than $4. In fact, you could order one right now; component retailers will sell you one for less than $15.

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  6. Re:no gadget required to detect the direction of by heinousjay · · Score: 4, Funny

    One of these days, your doctor will figure out the dosage and your posting will cease. Truly a sad day for all.

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  7. Re: You missed the point by Duggeek · · Score: 2, Insightful

    I know where you can BUMP and NUDGE to affect the gameplay... an actual PINBALL game!!!

    It's always irked me to see some hand-held P.O.S. that touts "realistic pinball action". (...action ...action ...ction ...tion)

    If I want to play pinball, I'll play pinball.

    However, if I want to ride a dragon... well I can't really do that now, can I?

    THAT is why the new controllers are so incredible; they give a new, visceral edge to creative gaming... rather than try to "come full circle" with a gaming platform that's already been around- and around- and around again.

    I'll grant you that someone will ultimately make a pinball-sized cabinet with two HD screens on it that uses the very implementation you describe. It will be neat, but it won't be real.

    You'll get a two-fold "wow factor" out of me when you can manufacture a true-physics pinball game that truly does something no other pinball game has done before. (Remember the face in "Fun House"? Now, that was some awesome innovation, back in its day.)

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  8. Oh CNN by bunions · · Score: 3, Insightful

    Sony Corp.'s "Sixaxis" controller for the PS3 also has an accelerometer. The six axises the name refers to are the three dimensions of space, plus three axises of spin. The company hasn't revealed who makes the chip.


    Axises?? How can you mispluralize one of the most entertaining plurals around? Axes, dammit.
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  9. oops! by MarcTheLad · · Score: 2, Informative
  10. Who was first? by Glacial+Wanderer · · Score: 5, Interesting

    The Nintendo Wii Remote one-ups the Sony controller by including an infrared camera.

    I think they meant to say: The Sony controller dumbed down the Wii Remote by excluding the infrared camera.

  11. datasheet by tonigonenstein · · Score: 3, Informative

    Right from the source: http://www.st.com/stonline/products/literature/ds/ 11115.pdf These things are not exactly new. They are used in the automotive sector, or for "stabilizers" in camcorders.

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  12. Re:Very odd by the.Ceph · · Score: 3, Insightful

    Consumer gear is often behind military tech. Perhaps you have heard of velcro, or GPS, or the internet.

  13. Re:Very odd by DerekLyons · · Score: 2, Interesting
    Given the 10+ year development and 20+ year use lifecycles of military equipment it's surprising to see consumer gear _behind_ military tech.

    It's hard to actually say who is ahead or behind, partly because tech in the real world isn't a linear scale (like it is in various games), partly because the military deploys such a wide variety of accelerometers. The ones used in, say the Trident-II's MK6 guidance, are certainly much larger than these (about the size of a film can) and are 'old style' (asymmetrical floats in fluid) - they are also much more robust and less sensitive to vibration. (The accelerometers in the MK6 Guidance System are also a neat illustration of the nonlinearity of tech in the real world. It uses an advanced form of the same type used in Polaris - because they are more sensitive and accurate than an advanced form of the (quite advanced in and of themselves) ones used in the MK5 guidance of the Trident-I.)
  14. Can we use this technology with the NES . . . by abscr · · Score: 3, Funny

    so I can finally keep Mario from falling down the bottomless pit by jerking the controller above my head?

  15. Re:camera problems by anotherone · · Score: 4, Informative

    It has accelerometers AND the sensor thing. Tennis actually just uses the accelerometers, it works quite well no matter where you're facing.

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  16. Re:Question for Slashdot by JCondon · · Score: 4, Informative

    Tilt sensors indirectly measure orientation (tilt). They look at the change in the gravitational acceleration vector with respect to the sensor coordinate frame.

  17. No fatigue by exp(pi*sqrt(163)) · · Score: 2, Interesting

    I was worried that something like metal fatigue would set in. But metal fatigue is a result of microscopic fractures in the crystalline structure of the metal. These sensors have moving parts that are fabricated from a single flawless crystal. So nothing like metal fatigue can take place.

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  18. Position sensing with the wiimote by bVork · · Score: 2, Insightful

    I found this absolutely fascinating video that shows exactly how the sensor bar detects the Wiimote's position - and how you can possibly hack up your own "sensor bar": http://www.youtube.com/watch?v=JTGSkYRDpWY

  19. wii console, remote and sensor bar by asjk · · Score: 2, Interesting
    The Nintendo Wii Remote one-ups the Sony controller by including an infrared camera. It picks up signals from a sensor bar the owner attaches to the television set. This enables the remote to "know" where it is in relation to the screen, so the player can use the controller to point to things on the screen -- a useful feature in shooting games (and a lot of games are shooting games).
    Here's another interesting piece of information. According to this source, the sensor bar is not even communicating with the console! I guess it's just shooting out a reference point for the remote, to act like a virtual mousepad to the remote's mouse?