## Accelerometer rotation around Z-axis

General project help for Adafruit customers

### Accelerometer rotation around Z-axis

I've been trying to reason out this theory problem in my head for most of the night. Here is the scenario, if I place the 3-axis accelerometer with Z pointing up with this axis going through the exact center of a rotating disc (like a banned type disc).

The question is if I start turning that disc around z and speeding it up to a desired rotational speed what will the reading be on both the XY? (keep in mind the accelerometer can read in both the positive and negative direction).

In my mind I figure the force in the positive X direction is the inverse vector of the force in the negative X direction and will give a result of 0g. Likewise with the Y direction. The only problem is...this seemed too easy an answer. Am I overlooking some (most likely basic) physics property that I've forgotten from school? And also if this is correct on paper does anyone know how it works in reality with the sensor?

Thanks
Krebstar4000

Posts: 5
Joined: Fri Mar 16, 2012 10:10 pm

### Re: Accelerometer rotation around Z-axis

having never played with accelerometers, this is just my interpreation of the scenario you painted ... the acceleration reported by the device in both the X and Y planes will be sinusoidal, and out of phase to eachother by 90 Degrees, while the Z-axis will (should) report a steady-state Zero
I look forward to comments byu the more experienced here ...
C
CharlieD

Posts: 25
Joined: Thu Mar 11, 2010 1:14 pm
Location: Natal Midlands, South Africa

### Re: Accelerometer rotation around Z-axis

I would assume that an accelerometer would measure centrifugal force since that is an acceleration. However, in an idealized experiment set exactly at the axis of rotation, the force should be zero. a = v^2/r and r = 0 so acceleration should be 0. In practice, I think it's very hard to perfectly align the accelerometer. Plus, there will also be some offset that needs to be compensated.
philba

Posts: 387
Joined: Mon Dec 19, 2011 5:59 pm