Shaft coupler for Robofocus

I know this is a long shot but I'm going to try.

I'm searching for a slip clutched shaft coupler. I want to mount my Robofocus motor to my stock Tak focuser and still have the manual focus knob option.

I found the perfect coupler at Mcmaster-Carr. It's a Precision, adjustable Torque-Limiting, Flexible Coupling with zero backlash, but it's $340. 8O

Has anyone tried this before and maybe have a cheaper alternative?
Thanks,
Bob Hayes

Hi Bob,
Look up McMaster-Carr part #: 9132k11
It's under miniature slip clutches, page 993.
When you want to disengage the RoboFocus, you just turn the clutch.
You lose the 'Home' position for the focus travel when you do this, so you'll probably want to recalibrate it every so often so you don't get into trouble.
Here's a blurry image of this clutch:
http://members.cox.net/dakoan/Jenkins%20bracket,2.jpg
I hope this helps,

dan kowall