Jo wrote:
In ,
Steve Taylor typed:

Why don't you close the loop and have proper position feedback ?



I was working with whatever bits and pieces were to hand. Any suggestions on
how to provide a positional feedback loop with typical junkbox items would
be cool. Come to think of it....there is a component in the VCR that *may*
be a linear position sensor..possibly for mechanically detecting how much
tape was remaining on a reel during fast rewind. Not sure of the resolution,
though. Any other ideas?

How many turns does the final drive from the motor make with the actual
focussing mechanism ? You could just detect position by inference from
the rotation of the drive wheel- use a multi-turn pot ( 6 quid)

Linear plastic pot ?

Shaft encoder from a mouse ? I'm also pretty sure that there are
encoders in VCRs. Have one fixed stop in your focusser. Drive onto the
stop and set your zero reference. That would need get nasty if you stick
with an analogue servo though - you'd need a counter and DAC to get a
voltage to drive the loop....not for the faint hearted.

What kind of positional resolution would you need I wonder ?

Steve