Jon,
Think a teeter totter. Bar with center pivot. When you pull on one side - the other side pushes and vice verse.
Set it up between the handle and the Bullfrog - you get opposite reaction. You can also vary the positioning fastening from the center pivot to have differing throw length desired.
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lever_and_crank(s).jpg [ 16.3 KiB | Viewed 6869 times ]
-ed-
_________________
-ed mccamey-
COSLAR RR -
http://www.coslar.us/NMRA Standards and Conformance Department
PROTO & FINE Scale Coordinator
I estimate I have about 5 pounds of coupler springs somewhere in the vicinity of my workbench.