Lift Yourself

Hello and welcome to "Lift Yourself Pulley System"

Less than 16% of high school students are interested in a STEM career. Hundreds of students tour The University of Texas at Dallas every year, but they do not always get a chance to see and interact with engineering displays which might get more students interested in engineering. The goal of our project, “Lift Yourself”, is to get high school students interested in engineering by showing them what an engineer is capable of doing. “Lift Yourself” is an interactive pulley system that uses pulleys and basic mechanical engineering principles to provide the seated user with the required mechanical advantage to lift themselves easily by just pulling on one rope. To further enhance the experience, the user will be given the option to choose from multiple different pulley systems each of which has a unique mechanical advantage. This will help explain what topics engineers study and what they do.

Major Components

Frame:

Made from 2"x2" Aluminum extrusions which can bear high loads

Linear Bearing:

Allows the chair to slide vertically with minimal friction

Pulley Configurations:

3 different pulley configurations each with a unique mechanical advantage; amplifies the input force to make lifting one's self easier

Rope:

Goes through the pulleys transmitting input force to output force

Redirect Pulleys:

Guide the rope and redirect the force

Wooden Floor:

Allows the rope to pass underneath and stores excess rope

How Does it Work?

1- Pulley Box:

The science happens inside what is called "The Pulley Box." This part of the display is where the pulleys are connected one to another to form 3 different pulley configurations, each with a different number of pulleys. To make it simple, as the number of pulleys increase in a configuration, the more mechanical advantage the user gets; which translated in differnt worlds to "it becomes much easier to lift yourself!"

We will use the notation "output:input" to tell the output force that the user will get when applying a certain input force.

Each one of the three pulley configurations has a different color rope to make it ease to see which pulley belongs to each configuration. The orange rope goes through "Configuration 1" which provides little mechanical advantage (2:1). The green rope goes through "Configuration 2" which provides the user with some mechanical advantage (4:1). Finally, "Configuration 3" provides the user with a huge mechanical advantage (10:1).

Afree body diagram that illustrates how the forces add up in each pulley configuration is shown in "Free Body Diagram" section!

2- Sliding Mechanism:

The "Sliding Mechanism" is both the bench and the sliding beam on which the bench is fixed. The Sliding Mechanism is connected to the Back Space frame using 4 linear bearings. There is also a Wooden Floor which allows the output rope to redirect from the Pulley Box, to the Back Space to lift the Sliding Mechanism and the seated user. The wooden floor also stores the excess portion of the input rope as the user pulls on it to lift themselves.

There is three color-coded input ropes in front of the seated user, each connected to a specific pulley configuration. If they wish to, the user can try lifting themselves without looking at the pulley configurations and try to guess how many pulleys there will be in each configuration based on the amount of input force they have to exert and the amount of rope being pulled!

This is the path which the rope for a single pulley configuration takes in order to transmit the force from the input location to the output location while passing through the pulley configuration in the Pulley Box.

Free Body Diagram

Configuration 1:

Configuration 1 has the least amount of pulley. Therefore, the free body diagram will have the least amount of forces when compared to configuration 2 and configuration 3.

Imagine that the input force you put gets broken down into the small "p" forces shown in the figure. The output force will be the "F" force. Now, to know how much output force you will get you must add up all the small p forces. In this configuration, you have 2 small p forces. Therefore, the mechanical advantage you get out of this configuration is 2:1; which means that if you exert a force of 5lb, you will get 10lb in return!

Configuration 2:

If we do the same counting for this configuration, we will notice that we have 4 small p. Therefore, the mechanical advantage for this configuration is 4:1.

Configuration 3:

The same applies to this configuration! The mechanical advantage will be 10:1 as there are 10 small p; which means that if you exert a force of 5lb, you will get 50lb in return!

Equations

Free Body Diagram:

There are two main steps to create a Free Body Diagram (FBD):

1- Draw the forces

2- Use Newton's First Law:

Newton's First Law can be understood as one single equation which is: The sum of all forces is one direction is equal to zero

The Mechanical Advantage ratio:

There is one important equation to calculate the Mechanical Advantage (MA) of a system:

MA = Output Force / Input Force
As a reminder, the input force in our system is the force which the user pulls the rope with (all the small p forces in the FBD); while the output force is F

Calculations

P = Input Force = User Provided Force

K = Output Force = Force after MA is applied = Input Force * MA

w= Your weight

W = Total Weight = w + weight of the bench (the bench weighs 50 lbs)

MA = Mechanical Advantage

In order to lift yourself, the input force must exceed the total weight

P > W / MA

Example Configuration 1

If you weigh 150 lbs then the total weight will be 150+50=200lbs; W=200

Therefore, with the 2:1 MA ratio that configuration 1 offers (MA = 2), the calculation will look as follows:

P > (200 / 2) = 100
You must must input at least 100 lbs of force in order to lift yourself!

Example Configuration 2

If you weigh 150 lbs then the total weight will be 150+50=200lbs; W=200

Therefore, with the 4:1 MA ratio that configuration 2 offers (MA = 4), the calculation will look as follows:

P > (200 / 4) =50
You must must input at least 50 lbs of force in order to lift yourself!

Example Configuration 3

If you weigh 150 lbs then the total weight will be 150+50=200lbs; W=200

Therefore, with the 10:1 MA ratio that configuration 3 offers (MA = 10), the calculation will look as follows:

P> (200 / 10) =20
You must must input at least 20 lbs of force in order to lift yourself!

Quick Lookup Table

Lookup your weight to know how much input force you exactly need in order to lift yourself using each pulley configuration!

PS: Do not forget to add 50lb for the weight of the bench!

Things to Look For

When using the display, look at how much you have to pull on each rope to lift he same distance!
- The higher the mechanical advantage is, teh more rope you have to pull to do the same work
Look at how many pulley are being added in each pulley configuration!
- The number of pulleys must be equal to "MA / 2"

- The MA is equal to "Number of Pulleys * 2"
When you are lowering yourself, look for what is helping you lower yourself!
- There is a "Gas Spring" connected onto the bottom of the bench to help you lower yourself safely

Real Life Examples

Cranes

Cranes that lift heavy weights require a lot of mechanical advantage to be able to do so easily. Cranes use many pulleys to make lifting objects much easier! [1]

Sail Boats

Pulleys have been used to assist in high load applications in sailing for thousands of years. These pulleys assist in operating the sails, lowering the anchor, and many more operations required in sailing! [2]

Fire Rescue

Pulleys can be used by firefighters to assist is saving someone who is injured or immobile. They can use the configuration shown to help lift the entire weight of the person in need to remove them from danger! [3]

References

[1] Selection and Maintenance of Crane Pulley. [Online]. Available: http://www.crane-manufacturer.com/blog/selection-and-maintenance-of-crane-pulley.html. [Accessed: 24-Nov-2020].

[2] “Boat, Sailboat Mast Strings Three-Masted Pulley #boat, #sailboat, #mast, #strings, #three-masted, #pulley: Sailing, Boat, Sailboat,” Pinterest. [Online]. Available: https://www.pinterest.com/pin/712976184732793871/. [Accessed: 24-Nov-2020].

[3] L. Boyle, “Learning the ropes: Firefighters prep for bridge work,” The Day, 28-Mar-2019. [Online]. Available: https://www.theday.com/article/20190328/NWS04/190329405. [Accessed: 24-Nov-2020].

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