I know there are some real physicists/mathematicians on the group, who will probably eat this problem for breakfast :-)

I am designing a machine which has a lightweight shaft that is turned by a small motor. I have to join the shaft to the motor with a coupling, and these come in different sizes, which are rated at different torque capacities, with units in inch-pounds.

My problem is that I have to select one size that will be able to handle the maximum torque put on it when the machine starts up. The two couplers I am looking at are rated at 3 inch-pounds, and 12 inch-pounds, and I would prefer the smaller one, with a shorter length, because of various aspects of the design.

The shaft, which is solid, weighs about 1 pound, is 1 inch in diameter, and the maximum torque comes from accelerating from 0 rpm to 400 rpm in approximately half a second.

My calculations so far, which may be completely wrong, are the angular velocity to be 83 radians per second, and my moment of inertia is 0.125 pound, but I can't see how to multiply these, and still get an answer in inch-pounds.

Any ideas?

Many thanks in advance

Richard in Los Angeles.

I am designing a machine which has a lightweight shaft that is turned by a small motor. I have to join the shaft to the motor with a coupling, and these come in different sizes, which are rated at different torque capacities, with units in inch-pounds.

My problem is that I have to select one size that will be able to handle the maximum torque put on it when the machine starts up. The two couplers I am looking at are rated at 3 inch-pounds, and 12 inch-pounds, and I would prefer the smaller one, with a shorter length, because of various aspects of the design.

The shaft, which is solid, weighs about 1 pound, is 1 inch in diameter, and the maximum torque comes from accelerating from 0 rpm to 400 rpm in approximately half a second.

My calculations so far, which may be completely wrong, are the angular velocity to be 83 radians per second, and my moment of inertia is 0.125 pound, but I can't see how to multiply these, and still get an answer in inch-pounds.

Any ideas?

Many thanks in advance

Richard in Los Angeles.

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