Angle between 2 Quaternions

Hi,

I have posted this same question on r/Mathematics,

I'm working on a Motion Capture suit for sports training (Tennis & Bing Bong). I'm using IMU 6050 and it's sending me Quaternions. Now the issue I'm having is how to get the Angle between joints, I have Two quaternions but I dunno how to get the accurate Angle between both of them (Forearm & Humerus for example) I (Calibrate at the beginning), then my Algorithm works as follows; 1- Get the difference for each IMU between the Calibration result, and the current result. 2- Get the Difference between the 2 Quaternions. 3- Calculate the Angle.

The point is that, it works perfectly in most of the movements, but it starts to give false data if I moved my body around a center point, and if I raised my hand high above.

I dunno if my algorithm is correct, but of course I have done research before using it.

Can anyone help me figure out the problem and how to solve it if possible?

submitted by /u/AZiada
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from math https://ift.tt/2I2k3vi