8-bar linkage

Grab the red point to move the linkage. It should make a very good approximation to a vertical movement along the black line, for the platform (the blue T-shape), over a fairly wide range of motions.

This kind of mechanism is used in theaters to move panels in the stage to get piano's (and ghosts) on an off.

Please enable Java for an interactive construction (with Cinderella).

The dots indicate the orbit for the mechanism. Move the black points in the list of parts to change the geometry and find a new orbit, maybe even straighter than the one depicted.

Created with Cinderella

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