This idea is not "tracking" - but does give basic motorised control....enough to keep the object in the viewfinder for a few minutes at a time...
https://www.youtube.com/watch?v=0V4lAv7nrsc
i got the idea from this:
https://www.youtube.com/watch?v=2NAlyq0Rf20
which i believe should be far better than mine....
cheers,