Input: orange gear shaft rotating at velocity Vi.
Output: green gear shaft that rotates in the same direction of the input.
When the orange gear is set to engage with the large blue gear, the output rotates at velocity V1:
V1 = Vi/((Z2Z4)/(Z1Z3))
Z1, Z2, Z3 and Z4 are tooth numbers of orange, large blue, small blue and green gears respectively.
In this video Z1 = 20; Z2 = 35; Z3 = 20; Z4 = 35 so V1 = Vi/3
When the orange gear is in mesh with green pins fixed to the green gear, the output rotates together with the input at velocity V2 = Vi.
The pink pin is used for fixing the orange shaft axially after adjustment.