Calculating Compost Cylinder Drive Motor Requirements

[fabricator]

Help required in order to determine required horsepower to rotate a steel hollow cylinde containing approx. 0.75 tons raw compost. the cyl. o/d is 1.8m., length is 2.8m. The cyl. is rotated about a central axis which is a 3inch o/d steel tube supported on 2 plumber block bearings.The cyl. req.s turning slowly 3rpm. once or twice a day.

 

[Danger]

Welcome to PF, Fabricator.
I can't help with any math stuff, but there is something missing from your description. Do you have "baffles" or "paddles" to ensure the mix being properly affected by the rotation? In any even, a definitive response would require some sort of resistance/friction factor.