for reducing gear collision.
Input: pink gear.
Output: green gear.
When the input rotates anti-clockwise, gear forces move the yellow idle gear out of its engagement with the output gear.
When the input rotates clockwise, gear forces move the yellow idle gear into contact with the output gear thus perform motion transmission.
The tooth top land must be rounded to prevent possible gear jam.
The mechanism should be used only for low speed because of collision.