I've got the sensor fusion code integrated with my application and working with my sensors, but this project has been reminding me just how long it's been since my last math class (coming up on 25 years, I think) and we never covered quaternions.
I'm running the 9DOF Kalman filter algorithm, and at the moment I'm just trying to get the 'down' angle in one plane. The sensor is in the rim of a large, relatively slow-moving wheel (maybe a few RPM) and I need to identify which part of
the wheel is in contact with the ground.
The pitch reading seems like the simplest way to go - if the sensor is at the bottom and level the pitch should be 0, after 1/4 rotation it'll be straight up and the pitch will be 90. The problem then is that it doesn't distinguish right side up from upside down and when the sensor is at the top and level it's back to 0. If the wheel wasn't moving it'd be easy - I could get what I need from a single accelerometer reading.
Which parameter(s) would be most appropriate for this?