How do I Design Pulleys?

Pulleys can make heavy lifting much easier.

Pulleys are simple machines that redirect force and can help you lift heavy objects with relative ease. With a pulley, you can lift an object high into the air by pulling down on a rope, allowing you to stay on the ground instead of having to somehow get above the thing you want to lift. If you have a job planned that involves lifting heavy objects, or lifting any objects while remaining standing on the ground, then you need to design a system of pulleys to help you with your job.

Things You'll Need

• Measuring tape

Instructions

1. Divide the weight of the object that you are planning to lift by the weight that you can lift comfortably, without straining yourself. This ratio is the mechanical advantage that your pulley system needs to get the job done.

2. Calculate the appropriate number of pulleys for your job. If you need a two-to-one mechanical advantage, then you need two pulleys. If you need a three-to-one advantage, you need three pulleys, etc. If you can comfortably lift the full weight of the object yourself, then you need no mechanical advantage and require only one pulley.

3. Measure the distance from the ceiling, tree branch or wherever you are going to hang your pulleys to the ground, in feet. Multiply this number by two. The result is the amount of rope you need to reach from the ground to the pulleys and back to the ground.

4. Multiply the width of the pulleys in feet by the number 3.14. The result is the circumference of each pulley, in feet. Multiply the number of pulleys in your system by this number to determine approximately how much rope will be needed to thread it all the way through your pulley system. Add this length to the length of rope you need to reach from the ground and back. The result is the total length of rope your pulley system will need.

5. Calculate the number of hooks you will need for your system. One pulley alone will need only one hook. Multiple pulley systems needs two hooks for each stationary pulley and one for each moving block. A two pulley system has one stationary pulley and one moving pulley. A three pulley system has one stationary pulley and two moving pulleys. A four pulley system has two stationary pulleys and two moving pulleys.

References

• K7NV: Block & Tackle Systems
• Construction Knowledge: Block and Tackle

Resources

• Crusader Education: The Block and Tackle