cr0sh:
...is this your first day on the internet?
Less than a day for me, but in the measure of you earthlings this is more than a century 
Seriously: I looked at amazon and in local toy stores. I'm not sure, if a server can move the load; and I have to convince my "secretary of finances" - these are quite expensive (especially for a first project).
oric_dan(333):
...
OTOH, I keep thinking I could do it all with 2 wide-beam sonars [40-deg each], and mount
them so as to have a small degree of overlap on the center edge of the beams. That way,
only one sonar would pick up an object moving in from the periphery, and would trigger
the servo to move them until both picked up the moving object simultaneously. Then, as
the object moved around, it would move out of one of the beams, and cause the servo
to move to track it.
...
I think this could be easier and more exact. Thanks!
And thanks for the two links.
best regards
Andreas