[Amps] "Best" limit indicators for multi-turn, shaft-driven gadgetry

[Martin A Flynn]

Jim,
Have you considered using an absolute position encoder on the stepper shaft?  This particular family will track up to 192 shaft turns, sending a a unique code for each position: http://www.stegmann.com/product/absolute/hollow.html

Money permitting this is what I will be using on my GS35B project.

Martin


-----Original Message-----
From: Jim Barber
Sent: Sunday, August 07, 2011 4:45 PM
To: Amps at contesting.com
Subject: [Amps] "Best" limit indicators for multi-turn, shaft-driven gadgetry

I've reached the point where I need to decide whether or not to make my
YC156 project amp "remote". Because of other interests, I already have a
good selection of larger stepper motors and drive electronics, and a
good feel for how to put it all together.

What I don't have is a good, simple limit stop/reference concept for the
vacuum caps and (possibly) roller inductor. I've used drive screws and
leaf switches in the past, but don't like the mechanical sloppiness and
complexity. I've also seen optical interruptors used in place of the
leaf switches, but still don't like the mechanical complexity of the
whole drive screw, platform and guide assembly.

My favorite candidate at the moment is a high-quality 10-turn pot in the
timing belt path for each shaft, "gearing it down" so that (for example)
a vacuum cap that rotates 13 turns end-to-end would run 8 or 9 turns at
the pot shaft. Using regulated 5VDC, I could then apply the output of
the (pot) divider to a 10-bit ADC. Note I already have ten 10-bit ADC
inputs at each control processor, so that isn't as much of a
complication as it might seem.

Any thoughts or suggestions?

Thanks,
Jim N7CXI