I/P: Orange shaft of a threaded portion at its middle, on which a blue gear with a friction disk is mounted (helical joint). The blue gear can move axial a little. Its displacement is adjusted by white nuts. The pink ratchet wheel rotate idly on the input shaft.
There is a green friction disk behind the ratchet wheel. It is fixed to the input shaft.
O/P: grey shaft of a big gear and a chain wheel.
The red arrow represents load (to be raised or descended) applied to the input shaft.
The blue arrows represent driving force applied to the input shaft.
The video shows three stages for the load:
1. Moving up: The input shaft is turned anticlockwise. Force at the helical joint pushes the blue disk to the right to contact with the ratchet wheel (forces it to the green disk). The ratchet wheel rotates together with the input shaft.
2. Stop (no driving force): The load tends to turn the blue disk clockwise and pushes it towards the ratchet wheel. The orange pawl brakes the load from descending.
3. Moving down: The input shaft is turned clockwise. Force at the helical joint pushes the blue disk to the left: no more contact with the ratchet wheel. The output shaft can rotate to descend the load. If the load descends faster than input velocity, the situation said in item 2 happens. The moving down is a jerk process.
The key factor is the right hand thread of the input shaft in this case.

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