I'm not sure this is the right place to pose this question, as it probably encompasses more than one field - EE, ME, programming, etc. But I'll ask the question anyway and hope that someone might have at least a general starting place.
Basically I would like to build a circular platform. On the platform will be four different objects. I would like the platform to rotate exactly 90 degrees when triggered via a computer (or by hand for a lower tech option) and then stop automatically.
Ideally it would be nice for the entire system to be automatic, but this isn't entirely necessary.
I'm assuming I will need some kind of electrical motor and belt for the rotation... beyond that I'm not sure how to go about implementing the automatic stop at 90 degrees. If someone were to start it by hand, I suppose they could also stop it, but it is importnt that it stop at exactly 90 degrees...
Any suggestions or ideas would be appreciated!