DC motor sizing

Hi,
How are you ??
i have the design in this picture
https://www.dropbox.com/s/ziye6s6v3xzsl4o/dc.jpg

i need to find the size of the dc motor
the torque required for this dc motor???

what the steps for such thing??
even if i can find any theoretical ffiles to explain this to be sure about this value ..
thanks

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