Not really, because pan, tilt, and roll ARE the rotation you are trying to measure.
So how can we measure anything if we ignore them?

Try taking a step back, and try to get the problem sorted out for JUST pan.
And extend the coding to tilt and roll only after PAN is working.

Also, try re-phrasing your question again. I think all us "experts" may have mis-understood
what it is that you actually want.
Do you want to find out how fast it is turning?
OR
Do you want to know its speed IN-SPACE, as in a sum of SpeedX & SpeedY & SpeedZ = TrueSpeed?
(that is its speed as a true distance, as-the-crow-flies)