Thanks guys,
Must confess I'm not thinking of 'goto' down the track, that's a level of complexity that I don't really need.
Having slept on the concept for a couple more nights, I realise that I'm not even really concerned with slewing to objects, as the mount moves very smoothly by hand.
I am interested in motorising the small fine movements when centering an object and in 'hand tracking' whilst observing. For that I reckon I can put something together.
With another small low rpm motor I found that a potentiometer does provide the speed variation I'm looking for. So this week I'll try it out.
Thanks again guys,
Chris