SparkFun Forums

[abagde]

I am currently using this accelerometer to measure the angle of incline while riding a bike. Basically I slightly modified the given code to calculate atan(x-measurement/z-measuement), and this is giving out the correct angle when the bike is stationary, at least in the -89 to 89 degree range. However, when I am riding the bike, the measurements are way off, the angle jumps all around the place. Is there a way I can phase out the effects of linear motion in my code?

[Mee_n_Mac]

I am currently using this accelerometer to measure the angle of incline while riding a bike. Basically I slightly modified the given code to calculate atan(x-measurement/z-measuement), and this is giving out the correct angle when the bike is stationary, at least in the -89 to 89 degree range. However, when I am riding the bike, the measurements are way off, the angle jumps all around the place.

Of course, you've just demonstrated the Equivalence Principle.
http://en.wikipedia.org/wiki/Equivalence_principle

Is there a way I can phase out the effects of linear motion in my code?

Phase out ... errr ... you can diminish the effects of acceleration via a low pass filter but off course that means your angle readings will be delayed. A magnetometer can measure your angle wrt to the Earth's magnetic field and is immune to acceleration but is sensitive to metal and stray magnetic fields.

[falingtrea]

You might try turning on the pulse LFP filter bit and taking a rolling sample of the data. That may smooth it out enough.

[Valen]

Are side-wheels an option? (joking.... somewhat)

As you are very likely causing the bike to swing left and right as you pedal. When the bike is leaning left and right due to the pedalling oscillation the Z-axis is not a true representation of the downwards gravity vector any more. The Y axis plays along in combination to the X axis. Your intended method only works for non-accelerated motions. And the left right oscillation is a form of acceleration.

[EDIT]Important to know: where is this accelerometer mounted? Mounted on the steering bars you might get even worse accelerations on top of it due to rotations.

[KeithB]

It is a little late now, but maybe an inclinometer would work better:
http://www.analog.com/static/imported-f ... S16209.pdf

[Mee_n_Mac]

That inclinometer measures the inclination be measuring the force of gravity and so will have the same problem.

[KeithB]

Yeah, but I am assuming it has internal software to compensate somewhat.

[smileyfujioka]

Hi abagde!

I am also using mma8452q. May I know what code/platform are you using? I am using lpc1769 and also facing a lot of troubles. Mind if you share your code? Thanks!

[Mee_n_Mac]

And to continue the necroposting ...

A video showing how accelerometers used as tilt sensors are affected by gravity.
https://www.youtube.com/watch?v=s19W-MG-whE