How to calculate a required torque of the motor

Hi Guys,
I am trying to calculate a required torque of the air motor powering the drum. The motor has to overcome 3000N resistance (tension) of the drum before it starts moving. The speed of the drum will be 6 RPM. Sprocket ratio is 6:1

My simple calculation would be

T=F*r (force * radius of the drum) so that would come up to 1800 Nm of torque. Now should I multiply those 1800Nm by 6 (ratio of the sprocket)?
See the attached picture.
Thanks

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See:

[URL="http://www.engineersedge.com/mechanics_machines/two_pulley_connecting_belt_design_and_calculations_10226.htm"]Two Pulleys Engineering and Design Calculations[/URL]

Also see the following:

[video]http://www.engineeringmotion.com/videos/1357/belt--pulley-calculations-video[/video]