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+--- Thread: "Acceleration without g" algorithm (/showthread.php?tid=1742)
"Acceleration without g" algorithm - martorino - 05-04-2023
I intend to develop an app that measures the centrifugal force applied to a skier making a series of turns.
I've found that using phyphox's "acceleration without g" option gives good results.
I ask to the authors of this excellent app (which I have been using with my students for some time) to learn more about the implementation of this specific algorithm.
Would it even be possible to have only the piece of code (presumably in Java or in any case in any high-level language) that interacts with the accelerometers (and the gyroscope) of the smartphone and performs this single type of measurement ? Would be the best !
Thanks in advance for any thoughts on this topic.
RE: "Acceleration without g" algorithm - Jens Noriʇzsɔɥ - 05-11-2023
The Android and iOS APIs support the “acceleration without g” right away (at least, as long as the required sensors are built-in) so there is no specific algorithm in phyphox. On other systems like microcontrollers, there are libraries supporting the so-called “sensor fusion” in order to remove “g” or compute an absolute position in space.
I find this series on sensor fusion rather instructive: https://www.youtube.com/watch?v=6qV3YjFppuc (if you want to go the hard way and implement it yourself
)
RE: "Acceleration without g" algorithm - martorino - 05-13-2023
Thanks for the info.
However if, as you say, there is no specific algorithm in phyphox to calculate centrifugal acceleration "without" g, then what is the difference between the two options (the first 2 above) "Acceleration (g included)" and " Acceleration (without g)" ?
I watched the suggested video (and also 2 others in the same section) but my knowledge of spoken English is not sufficient to fully understand what is illustrated there.
However, I understood the interesting concept of "sensor fusion" but I am not able, at the moment, to implement it in a high-level language (I usually use B4A) without further help.
RE: "Acceleration without g" algorithm - Jens Noriʇzsɔɥ - 05-15-2023
The algorithm that subtracts Earth‘s acceleration is provided by the OS. Both options, acceleration with g in- and excluded, are directly obtained from the sensor APIs. You could (likely) do the same with your Android framework without wondering how to implement any sensor fusion concepts…
The accelerometer “sees” Earth‘s acceleration, however, on many occasion that‘s not what you want in scientific experiments, centrifugal acceleration being one of these examples like you said. Sensor fusion with gyroscope and magnetometer allows to identify the direction of Earth‘s acceleration and accordingly “remove” it. Since the latest release of phyphox, there is also this virtual gravity sensor included in https://phyphox.org/wiki/index.php/Phyphox_file_format#Input_module:_sensor