The design is really simple: on both sides of a telescopic extension pole sit a fixture that can pan and tilt, using two hinges. The fixtures are identical, except for the camera mount.
The fixtures are connected to each other by 3 pieces of wire. The resulting effect is that if you move one fixture, the other fixture copies the exact movements.
The range of motion is about +/- 45 degrees left&right and up and down. As there are no pulleys or complex lever systems, the motion is pretty smooth. The hinges need some more work, they tend to stick a little and make some noise. I'll remove some material to make it smoother.
Here is the crane itself:
And here is some footage I shot with it