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Use your iPod for a dynomometer!

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Use your iPod for a dynomometer!


Old 08-15-2008, 01:22 AM
Worlok14's Avatar
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Default Use your iPod for a dynomometer!

Do you want your own private Dyno???

Now you can download a software and install it on your iPod touch or iPhone, if you fix the iPod/Phone on the car or bike the software will use the accelerometer that your device has in it to calculate intereting numbers... Some guys I know have done this already with their cars and even thou the numbers are not exact, they come pretty close to what you get in a Dyno...

Now before you call bullcrap, read this:

An accelerometer measures the acceleration and gravity it experiences. Both are typically expressed in SI units meters/second2 (m/s2) or popularly in terms of g-force.

The effects of gravity and acceleration are indistinguishable, following Einstein's equivalence principle. As a consequence, the output of an accelerometer has an offset due to local gravity. This means that, perhaps counter-intuitively, an accelerometer at rest on the earth's surface will actually indicate 1 g along the vertical axis. To obtain the acceleration due to motion alone, this offset must be subtracted. Along all horizontal directions, the device yields acceleration directly. Conversely, the device's output will be zero during free fall, where the acceleration exactly follows gravity. This includes use in an earth orbiting spaceship, but not a (non-free) fall with air resistance, where drag forces reduce the acceleration until terminal velocity is reached, at which point the device would once again indicate the 1 g vertical offset.

For the practical purpose of finding the acceleration of objects with respect to the earth, such as for use in an inertial navigation system, the correction due to gravity along the vertical axis is usually made automatically, e.g. by calibrating the device at rest.

Now the iPhone/iPod has a built-in accelerometer in order to detect in which position the device is being held (horizontal-vertical), this accelerometer is used by the device to calculate movement. This accelerometers are a copy of our internal hearing system (the one which is responsible for balance), and it was commercially used first in the segway vehicles...

Beleive it or dont!
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Old 08-15-2008, 02:31 AM
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i've actually heard of this already.
now, whether calibration and all is a concern, i'm not sure, as i'm not an accelleromoter

theres certain types of them, tho.. i know certain alarm shock detectors typically rely on a type of accellerometer in a way.

a basic type is a spiral spring mounted vertically on the circuit board. in dead center, not touching the spring, is a rod. when substantial force is exerted radially, the spring flexes over and touches the rod in the middle.

theres a certain amount of force is needed to make that happen, obviously.. but, this is pretty much a switch. not a sensor.

thers other types, and while i won't bore you with details on THEIR functions, i'd just be willing to bet that they're all not exactly suited for detecting forces and/or acceleration..

i dunno.. my .002 but i definitely have heard the iphone accellerometer trick.
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Old 08-15-2008, 03:26 AM
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I believe the iPhone uses a MEMS type accelerometer. There are several types of these, the simplest just detects the change of a small mass from a neutral position. Another type of MEMS device detects the deflection of a small bubble of heated air using a tiny thermocouple. I've used several types they all work very well.

For example, see the analog devices adxl202. I think the one in the iPhone might be made by ST Microelectronics, though, namely the LIS302 which is a 3-axis sensor.

I just got an iPhone so I may have to download this program and try it out. It probably works pretty well for a ballpark figure, but I'm not sure I'd base any truly important decisions on the result.
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