This is my first post on these forums, and I was hoping someone could answer a question I have. For my high school engineering course, we spend most of the year developing a solution to a problem of our choice. We are currently developing a composting tumbler that will turn automatically several times every other day. This is to ensure the quickest rate of composting based on factors such as aeration and microbial activity. A very simple 5 minute sketch below shows the basic design. There is a backup manual turning handle as well. My question pertains to the system that will be physically rotating the drum of the composer. What system would most efficiently rotate a drum? I have very little knowledge of rotational systems, but after some research it appears that pulleys are relatively inefficient due to slipping and stretching. That leaves me with a gear systems or a sprocket and chain system. An additional idea that I had could involve a piston (I believe they are called linear actuators?) rotating the drum (shown below), but I don't know if that would be feasible. The drum is a hollow cylinder with relatively thins walls and a maximum weight of 600 lbs (when filled with wet dirt), although the lower density of compost would likely mean a much lower weight in the range of 300 - 350 lbs when full. There is an axle through the center of the cylinder. We are currently researching the material that is best suited to make the drum out of, but I wouldn't think that the material properties other than weight will have any impact on the turning of the drum. I apologize since this is a very broad question and I am ignorant on the subject, but I was hoping someone could suggest what specific gear system, sprocket and chain, piston, etc. to use.