Pulley
v2.0
Curriculum Packet
Progression: Applications in Design & Engineering - Section 3
Introduction
This Rokenbok STEM-Maker lesson will use the following steps to learn
about the pulley.
2. Build
& Modify
1. Learn
Elements of a pulley
Purpose of a pulley system
Real world applications
Creating mechanical advantage with pulleys
3. Design
& Engineer
Build a fixed pulley system
Build a movable pulley system
Modify a pulley system
from 2:1 to 3:1 mechanical advantage
Design & engineer a custom pulley system to
solve a challenge
Learning Objectives
Resources
Understand the basic elements of a pulley.
Understand how a pulley redirects motion
and creates mechanical advantage.
Calculate the amount of mechanical
advantage in a pulley system.
SnapStack
Module
Modify a pulley system to increase
mechanical advantage.
*4 Students Per Module
or
Programmable
Robotics Module
or
*4 Students Per Module
Advanced
Projects Lab
*4 Students Per Lab
Design and engineer a custom pulley system.
Key Terms
Simple Machine: A device that transmits or modifies force or motion.
Force: A push or a pull.
Pulley: A simple machine consisting of a wheel with a grooved
rim in which a pulled cable can change the direction of the pull
an thereby lift a load.
Work: Using a force to move an object a distance.
Mechanical Advantage: The amount a machine multiplies force.
Load: The object or weight being moved or lifted.
Effort: A force applied to a machine to do work.
1
Building Basics
Rokenbok Building Basics
The following tips will be helpful when using the Rokenbok Student Design & Engineering System.
Connecting/Separating ROK Blocks:
ROK Blocks use a friction-fit, pyramid and opening system to connect. Simply
press pyramids into openings to connect. To separate blocks, pull apart.
Connecting/Separating Rokenbok Components:
Smaller Rokenbok components use a tab and opening system to connect. Angle
one tab into the opening and snap into place. To separate, insert key into the
engineered slot and twist.
Snapping Across Openings:
The tabs on Rokenbok components can also be snapped across openings to
provide structural support to a design. This will also allow certain designs to
function correctly.
Attaching String:
In some instances, string may be needed in a design. Lay string across opening.
Snap any Rokenbok component with tabs or pyramids into opening. Make sure
tabs run perpendicular to string for a tight hold.
Measuring:
2cm
3 Openings
9 Openings
The outside dimensions of each Rokenbok connector block
are 2cm3. This cubic notation (cm3) means the length,
depth, and height are each 2cm. To determine the size of a
Rokenbok build in cm, simply count the number of openings
and multiply by two. Repeat this process for length, depth
and height.
2cm
18cm
2cm
2
6cm
Learn
Wheel
The Pulley
A pulley is a simple machine that consists of a wheel and axle with
a groove cut into the edge of the wheel to accept a cable. The pulley
allows the cable to be attached to a load and transfers the downward
pull of the cable to raise the load.
Purposes
Cable
Axle
Example 1 - Single Fixed Pulley
Pulleys can be used to redirect motion or to reduce the amount of effort
needed to raise a load by creating mechanical advantage.
Redirecting Motion
Fixed
Pulley
Effort
In a single fixed pulley system (example 1), the amount of effort needed to raise the load
must be more than the load itself. For example, if the load was 100lbs, a force greater
than 100lbs would be needed to raise the load. A single fixed pulley system is only used
to redirect motion. If a user pulls down on one end of the cable (Effort), the other end
(Load) will raise up an equal distance in the opposite direction.
Example 2 - Movable Pulley
Fixed
Pulley
Creating Mechanical Advantage
Pulleys are used to reduce the amount of effort needed to raise a load by creating
mechanical advantage. To create mechanical advantage in a pulley system, a movable
pulley must be attached directly to the Load (example 2). A movable pulley system
trades increased distance for reduced Effort.
Effort
Pulleys are used in many different ways to make work easier. Here are some real world examples.
Water Well
Flag Pole
Crane Truck
3
Moveable
Pulley
Load
Real World Applications
Block & Tackle
Load
Belt Pulleys
Build & Modify
Instructions
Follow the step-by-step instructions to build a pulley system.
1
2
4x
Block
2x
Beam
3x
Half Beam
2x
Riser
3
1x
Block
3x
Beam
1x
Half Beam
3x
60° Block
3x
30° Block
3x
Beam
4
2x
Half Beam
3x
Single Snap Block
Build & Modify
Instructions
Follow the step-by-step instructions to build a pulley system.
4
3x
Block
5
4x
Half Beam
2x
Riser
2x
60° Block
6x
Single Snap Block
1x
String Block
6
5
5x
Pulley
Build & Modify
Instructions
Follow the step-by-step instructions to build a pulley system.
7
8
5 Blocks
Separating
Markers
Top Markers:
Upside-Down
10 Blocks
Separating
Markers
Cut a piece of string that is 40cm
long. Feed each end of the string
through the single snap blocks as
shown. Lay string on top of the red
connector blocks and snap into
place. Once connected, place string
of weights over fixed pulleys.
Middle/Bottom Markers:
Right-Side Up
4x
Trailer Hitch
2x
Block
9
2x
Snap-In Wheel
2x
Single Snap Block
String Block
Assemble two weights using the listed components. Cut
a piece of string that is 50cm long. Tie a knot in one end
of the string and place knot in string block to secure into
place. Feed other end of the string through the fixed pulleys
and movable pulley (weight 2) as shown. Connect string to
weight 1 to secure in place.
Top Markers
Weight 2
Note: Adjust string if necessary so that when weight 1 is
resting on frame, top of weight 2 is even with top markers.
2x
Block
Weight 1
2x
Snap-In Wheel
1x
Pulley
6
1x
Single Snap Block
Build & Modify
Testing Pulley System
Follow the instructions below to test both sides of the Rokenbok Pulley Model.
Fixed Pulley (Redirecting Motion)
Fixed Pulley
Fixed Pulley
Turn the pulley system so that you can test the fixed pulley system. Observe how
the weights balance each other out. Pull down on Weight 1 (Effort) and observe
how Weight 2 (Load) moves an equal distance in the opposite direction.
Weight 1
Effort
Fixed Pulley System
Fixed
Pulley
Weight 2
Load
Fixed
Pulley
Effort
Load
Movable Pulley (Mechanical Advantage)
Turn the pulley system around to the side with the movable pulley. Lift Weight
1 (Effort) until the top is even with the top markers. At this point, Weight 2
(Load) should be even with the middle marker. Let go of Weight 1 (Effort) and
observe how it is able to raise Weight 2 (Load) to the top markers.
Top
Markers
Movable Pulley System
Fixed
Pulley
Middle
Marker
Fixed
Pulleys
Moveable
Pulley
Weight 2
Load
Weight 1
Effort
Effort
Low
Marker
Load
7
Build & Modify
Understanding Mechanical Advantage
Fixed Pulley System
The main purpose of a simple machine is to make work easier.
This means either redirecting motion or creating mechanical
advantage. Mechanical advantage exists when the output force
of a machine is greater than the input force that was applied to
it. To accomplish this, the machine must trade increased time or
distance for reduced effort.
Weight 1
Effort
Weight 2
Load
Calculating Mechanical Advantage
Calculating the mechanical advantage in a pulley system can be done by dividing
the distance the effort travels by the distance the load travels. If the pulley system
has a movable pulley, the number of strings connected to the movable pulley can
also be used to determine the mechanical advantage.
Distance Formula
Mechanical
Advantage
=
Distance effort travels
Distance load travels
Movable Pulley Systems
# of strings
connected to
movable pulley
=
Movable Pulley System
Mechanical
Advantage
Fixed Pulley System
In the fixed pulley system, if Weight 1 (Effort) is pulled down, then weight 2 will
raise and equal amount in the opposite direction. Divide 8/8 and this will give a
mechanical advantage of 1:1. This means that for every unit of measurement the
effort travels, the load will travel an equal unit of measurement in the opposite
direction. This demonstrates how there is no mechanical advantage in a fixed
pulley system. In order to raise one of the weights, extra effort or mass would be
needed to overcome the mass of the load.
Weight 2
10 cm
Load
Weight 1
10 cmWeight 1
Effort
(Effort)
Weight 2
(Load)
Movable Pulley System
In the movable pulley system, Weight 1 (Effort) travels a distance of 10 blocks
(20 cm). Weight 2 (Load) travels a distance of 5 blocks (10 cm). Divide 20/10 and
this will give a mechanical advantage of 2:1. This means that for every two units
of measurement the effort travels, the load will travel one unit of measurement
in the opposite direction. There are two strings connected to the movable pulley
in this example, which also confirms that this pulley system has a mechanical
advantage of 2:1. This pulley system is able to output a greater force than the
input force that was applied to it.
Modify: Pulley System
Now that you have built a pulley system that has
a mechanical advantage of 2:1, slightly modify the
system to increase the mechanical advantage to 3:1.
8
Effort - 20cm
Load - 10cm
=2
2 of strings
connected to =
movable pulley
2
Design & Engineer
Design & Engineering Challenge: Pulley System
In this challenge, each team must design and engineer a custom pulley system. Read carefully through the design
brief below, then use the Design & Engineering Process to develop a solution to the challenge.
Design Brief: Scenario
Go-Cart Assembly
You have just inherited a motorized go-cart from your uncle. It
is in good shape, but needs an oil change before you can ride it.
The drain plug for the oil is underneath the go-cart frame so it is
difficult to change the oil while it is on the ground.
Design & Engineering Challenge
Your design challenge is to design and engineer a pulley system
that can raise and lower a go-cart so routine maintenance can be
done on it.
1x
Block
4x
Snap-In Wheel
1x
Corbel
1x
Single Snap Block
1x
Riser
Specifications & Sub-Challenges
1. Teams can work in groups of up to four to complete this challenge.
2. Teams must work through each step of the Rokenbok Design & Engineering process to design, prototype, and refine a custom pulley system. Teams will be responsible for written documentation in the student engineering workbook.
3. Sub-Challenge: The pulley system must raise the go-cart at least 18cm off of the ground.
4. Sub Challenge: The pulley system must be able to carefully lower the go-cart back to ground level.
5. Sub-Challenge: The pulley system must feature a safety locking pin to keep the rope or cable in place while being worked on.
6. The pulley system must be aesthetically appealing.
7. Sub-Challenge: The pulley system must create mechanical advantage.
8. With each building component costing $2, the pulley system must cost less than $120.
(The components in the go-cart do not count towards the budget of $120).
9. Each team will be required to effectively explain all aspects of brainstorming, prototyping, testing and improving the custom pulley system. Teams will also be responsible for explaining how the pulley system works and creates mechanical advantage.
Design & Engineering Process
To develop a high quality design, teams will work through
each step of the design & engineering process. Teams
should track all progress in the student engineering
workbook.
Design and Engineering Process
9
Student Engineering Workbook
Design & Engineer
Challenge Evaluation
When teams have completed the design & engineering challenge, it should be presented to the teacher and classmates
for evaluation. Teams will be graded on the following criteria:
Specifications: Does the design meet all specifications as stated in the design brief?
Performance: How well does the design work? Does it function consistently?
Team Collaboration: How well did the team work together? Can each student descibe how they contributed?
Design Quality/Aesthetics: Is the design of high quality? Is it structurally strong, attractive, and well proportioned?
Material Cost: What was the total cost of the design? Was the team able to stay on or under budget?
Presentation: How well did the team communicate all aspects of the design to others?
Grading Rubric
Advanced
5 Points
Proficient
4 Points
Partially Proficient
3 Points
Specifications
Meets all
specifications
Meets most
specifications
Meets some
specifications
Does not meet
specifications
Performance
Design performs
consistently well
Design performs
well often
Design is partially
functional
Design does
not work
Team Collaboration
Every member of
team contributed
Most members of
team contributed
Some members of
team contributed
Team did not
work together
Design Quality/
Aesthetics
Great design/
aesthetics
Good design/
aesthetics
Average design/
aesthetics
Poor design/
aesthetics
Material
Cost
On Budget
($120 or Less)
Slightly Over
Budget ($120-130)
Over Budget
($130-140)
Significantly Over
Budget ($141+)
Great presentation/
well explained
Good presentation/
well explained
Poor presentation/
explanation
No presentation/
explanation
Presentation
Not Proficient
0 Points
Points
/30
Total Points
55-01191-200
10