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Transfer of torque along a pedal powered drivetrain?

Topic Type: 

Recently began researching Pedal Powered agricultural machines, more specifically grain cleaning machines. Have found some great videos of finished products. Ultimately wanting to build something to clean and dehull millet and/or sorghum. I am getting hung up on Torque and how it applies after the initial torque from the pedals. If the sprocket on the pedals is connected to an axle with a smaller sprocket, and on that same axle is another, larger sprocket which is linked to something further down the drivetrain how does the initial torque from the pedals transfer to the larger sprocket and so on down the line? Any information or resources would be greatly appreciated. Thank you, Hackers.

Gwyn Jones's picture

If I follow your question, you are interested in understanding how much torque will be available along your drivetrain.  You have pedals on a shaft with a sprocket driving a chain, that drives a smaller sprocket on another shaft.  The torque, or rotational force, starts through the system at the pedal.  Making some assumptions for the sake of an example, let's say the pedal arm is 7 inches long and the sprocket is 8 inches in diameter or 4 inches in radius.  If you push down with a force of 100 pounds on the pedal 7 inches from it's rotational center, and the sprocket transfers the force into the chain 4 inches from the rotation center, the force will be the ratio of 7 to 4 times 100 pounds of force or 175 pounds of force in the chain.  If the second shaft has a sprocket driven by the first chain of 4 inches in diameter and a larger sprocket of 8 inches in diameter the second chain will transmit force in a ratio of 1 to 2 times the 175 pounds of force in the first chain or 87.5 pounds of force.