What I did: estimated Q factor

I tryed to measure Q factor of Roberts Linkages that resonant frequency is 0.67Hz by ring down curve.
When I estimated Q factor, I used the data from 500s to 1400s (just Fig 2).
Estimated Q factor is 5.97×10^3.

Blue points are measurement and red points are fitting.
Vertical axis is read out of photo sensor that can detect displacement, horizontal axis is time.
Fig 1 is over view of the ring down curve.
Fig 2 is the data that is used for estimating Q factor.
Fig 3 is over view and fitting results.
Fig 4 is the ring down curve that is used for estimating Q factor and fitting results.
Fig 5 is also the ring down curve and fitting results from 600s to 620s.