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Progression: Applications in Design & Engineering - Section 3 Curriculum Packet
Pulley
IntroductionThis Rokenbok STEM-Maker lesson will use the following steps to learn about the pulley.
Key Terms
Simple Machine: A device that transmits or modifies force or motion.
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.
Mechanical Advantage: The amount a machine multiplies force.
Force: A push or a pull.
Work: Using a force to move an object a distance.
Effort: A force applied to a machine to do work.
Load: The object or weight being moved or lifted.
Learning Objectives
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.
Modify a pulley system to increase mechanical advantage.
Design and engineer a custom pulley system.
Resources
SnapStack Module
*4 Students Per Module
Programmable Robotics Module
*4 Students Per Module
Advanced Projects Lab
*4 Students Per Lab
or or
Elements of a pulley Purpose of a pulley system Real world applications Creating mechanical advantage with pulleys
1. Learn 2. Build & Modify
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
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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.
2cm18cm
9 Openings
6cm
3 OpeningsMeasuring:
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
2cm
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The PulleyA 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.
PurposesPulleys can be used to redirect motion or to reduce the amount of effort needed to raise a load by creating mechanical advantage.
Redirecting Motion
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.
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.
Real World ApplicationsPulleys are used in many different ways to make work easier. Here are some real world examples.
Learn
Example 1 - Single Fixed Pulley
FixedPulley
Effort Load
Example 2 - Movable Pulley
FixedPulley
Effort
Load
MoveablePulley
Block & Tackle Water Well Crane Truck Flag Pole Belt Pulleys
Wheel
Cable Axle
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Build & Modify
InstructionsFollow the step-by-step instructions to build a pulley system.
4x Block
2x Beam
3x Half Beam
2x Riser
2
3x Beam
2x Half Beam
3x Single Snap Block
3
1x Block
3x Beam
1x Half Beam
3x 60° Block
3x 30° Block
1
5
Build & Modify
InstructionsFollow the step-by-step instructions to build a pulley system.
3x Block
4x Half Beam
2x 60° Block
6x Single Snap Block
2x Riser
6
1x String Block
5x Pulley
4 5
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Build & Modify
InstructionsFollow the step-by-step instructions to build a pulley system.
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4x Trailer Hitch
10 BlocksSeparating
Markers
5 BlocksSeparating
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.
2x Block
2x Snap-In Wheel
2x Single Snap 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.
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
2x Snap-In Wheel
1x Pulley
1x Single Snap Block
String Block
Top Markers
Weight 1
Weight 2
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8
Top Markers:Upside-Down
Middle/Bottom Markers: Right-Side Up
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Build & Modify
Testing Pulley SystemFollow the instructions below to test both sides of the Rokenbok Pulley Model.
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 1Effort
Weight 2Load
Fixed Pulley Fixed PulleyFixed Pulley (Redirecting Motion)
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.
Weight 1Effort
Weight 2Load
MiddleMarker
LowMarker
TopMarkers
Movable Pulley (Mechanical Advantage)
Fixed Pulley System
FixedPulley
Effort Load
FixedPulley
Movable Pulley System
Effort
Load
FixedPulleys
MoveablePulley
FixedPulley
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Understanding Mechanical AdvantageThe 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.
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.
Modify: Pulley SystemNow 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.
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.
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.
Movable Pulley Systems
# of strings connected to
movable pulley
MechanicalAdvantage=
Weight 1Effort
Fixed Pulley System
Weight 2Load
Movable Pulley System
Weight 1(Effort)
Weight 2(Load)
Effort - 20cmLoad - 10cm = 2 = 2
2 of strings connected to
movable pulley
Build & Modify
10 cm
10 cm Weight 1Effort
Weight 2Load
Distance Formula
Distance effort travels Distance load travels
MechanicalAdvantage =
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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 & 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 engineeringworkbook.
1x Riser
1xBlock
4x Snap-In Wheel
1x Corbel
1x Single Snap Block
Go-Cart Assembly
Design & Engineer
Design Brief: Scenario
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.
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 and Engineering Process Student Engineering Workbook
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Design & Engineer
Challenge EvaluationWhen 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?
Specifications
Performance
Team Collaboration
Design Quality/Aesthetics
Meets all specifications
Design performs consistently well
Every member of team contributed
Great design/aesthetics
On Budget ($120 or Less)
Great presentation/well explained
Good presentation/well explained
Poor presentation/explanation
No presentation/explanation
Over Budget ($130-140)
Significantly OverBudget ($141+)
Most members of team contributed
Good design/aesthetics
Average design/aesthetics
Poor design/aesthetics
Some members of team contributed
Design performs well often
Design is partially functional
Design does not work
Team did not work together
Meets most specifications
Meets some specifications
Does not meet specifications
Material Cost
Presentation
Points
Total Points
Proficient4 Points
Advanced5 Points
Partially Proficient3 Points
Not Proficient0 Points
/30
Grading Rubric
Slightly OverBudget ($120-130)
55-01191-200