Freematics Forum

According to this post viewtopic.php?f=2&t=1982&p=3936&hilit=acceleration#p3936
in order to get my acceleration in the units of m/s^2 I need to multiply it by the following factor:
160(to correct approximation done in original code) * 9.81(value of g)/ 16384

I performed this transformation with my data. However, something is not adding up. The max acceleration magnitude (sqrt(x^2 + y^2 + z^2)) is only about 0.9 g (which would only make sense if the car were constantly falling ).

Am I missing something or perhaps the calibration should be different?

Thank you

But... isn't it technically always falling? Otherwise, you'd fly off into space

@promotor funny.
No, it isn't. I suspect you know this, but just in case, technically speaking satellites and spaceships are constantly falling, that's why astronauts (and cosmonauts) on the orbiting space stations are weightless, they exert 0 force on the place they are "standing" on. An accelerometer in a stationary car should show the acceleration of 9.8 m/s^2, i.e. g. It doesn't mean that the car is falling, but that the accelerometer is acted upon by the base it is on with the force that produces acceleration g (if the car is horizontal that would be the normal force, if not, you'd have to add the tire traction force)

Yep! So I'm not getting your question. Shouldn't the accelerometer always read ~1g in the down position when sitting still? Or is that not what your original post is saying.

My post says that the maximum magnitude of my acceleration is 0.9*g. The median is around 0.86*g. In other words, my acceleration never reaches g.

Ah I get it. Well I don't know then. Maybe your car is REALLY slow.

It may be the bias of the dongle, plugged into the OBD-II Data Port -- it's unlikely to be pointed straight down, and so the full 1G of force is not going to be exerted on that single axis. When positioned at some other angle, the planet's gravity will be applied across more than one axis.