Input: the blue gear-shaft. Output: the yellow shaft.
The white crank, carrying cyan gear-shaft, can oscillate around a fixed axle. Two grey disks have sliding key joints with the cyan gear-shaft. The pink and orange disks have sliding key joints with the yellow shaft. The blue spring forces four mentioned disks towards the yellow disk.
Turn the blue screw to change contact place between the disks (near or far from the center of the grey disks), hence the output velocity.
Transmitted power can be increased by using more pink and grey disks.