If you're designing a system for hoisting a load using a pulley and a motorised winding drum, you must space the drum and the pulley sheave apart far enough to maintain a safe "fleet angle." The fleet angle of a sheave-and-drum pulley system refers to the maximum angle from the front of a fixed sheave to the outermost position along the drum as it winds the fibre (e.g., rope, cable or wire). If the angle is too small, you'll won't be able to wind enough fibre for the system to be useful; if the angle is too large, the fibre will be pulled off the sheave's track, requiring you to shut down and repair the system.
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Things you need
- Graphing calculator (optional)
Measure the direct distance from the front of the fixed sheave to the axis of the drum (in feet).
Measure the length of the smooth-faced drum from the centre to the left edge (in feet).
Divide the result from Step 2 by the result from Step 1.
Calculate the arctangent of the result from Step 3. This is the left fleet angle of the drum.
Measure the length of the smooth-faced drum from the centre to the right edge (in feet).
Divide the result from Step 5 by the result from Step 1.
Calculate the arctangent of the result from Step 6. This is the right fleet angle of the drum.
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