I have a real world system I am analyzing consisting of actual mechanical components that oscillate by rotating back and forth in a fixed axle (kind of like those finger fidget spinners but my system oscillates back and forth in its rotations within an angle bandwidth instead of endlessly rotating in the same direction).
I would like to obtain the frequencies at which these components are doing their back and forth oscillations.
Which kinds of frequency values is most reasonable to request from my DSP package when doing my FFT? Only positive absolute values? All absolute values? Only positive complex values? All complex values?
My gut is telling me that I might want to stay away from anything dealing with complex values, since my oscillations are from a real-world system and might therefore only be a real-valued function (?), but to be honest, I don't know if his is a fair assessment (I am dipping my feet into DSP for my present project so not a pro in the field).
If there's a justification for picking one over the others, I am interested in hearing it. Thanks for any recommendations anyone can give.
EDIT: What I am feeding to the DFT is my angle vs. time data and I'm interested in identifyig the frequencies which are found in the oscillation rotation behavior.