Geometry For Linked Contra Rotating Shaft

[DonR62]

Hello,

I'm trying to work out (and failing) if it is geometrically possible to link two parallel shafts so that when either is driven they contra-rotate by equal amounts (in degrees). Range of movement I'm concerned with is 90 degrees maximum. Any tips on how to go about working it out?

 

[3DDave]

This is usually done with gears on the shafts that are either in direct contact or through pairs of intermediate gears. If it's small enough a flax shaft could also suffice.

If you used a scotch-yoke that is constrained to hold the slot horizontally and pins on both the shafts, that would synchronize the motion over the short rotation.

https://www.youtube.com/watch?v=dqDHfOBE8EQ

This is a constant ratio linkage - however there is a dead spot which means that the driven gear needs inertia to carry it through.