Bell crank and lazy-tong linkages
I can make bell crank and lazy-tong linkages.
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Lesson details
Key learning points
- A bell crank linkage moves levers at angles from each other.
- A lazy-tong linkage is made of levers which lengthen or shorten when one end is pushed or pulled.
Keywords
Linkage - A mechanism connecting levers together.
Input - The motion used to start a mechanism.
Output - The motion created by the input.
Loose pivot - A free moving point that connects two levers together.
Fixed pivot - A point that connects a lever to one place.
Common misconception
It doesn't matter where you place the pivots on a lazy-tong linkage.
Where the pivots are placed is very important on a lazy-tong linkage. If they are not placed correctly, the mechanism will not function correctly.
Equipment
See additional resources document for a list of materials needed for this lesson.
Content guidance
- Risk assessment required - equipment
Supervision
Adult supervision required
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Match the linkage to the description.
The output moves in the same direction as the input.
The output moves in the opposite direction to the input.
Works in the same way as the push pull linkage.
Q2.Which of these best describes a mechanism?
Q3.What type of linkage is this?
Q4.Which of these would be the most suitable for a pivot point in cardboard?
Q5.Fill in the missing word. A simple lever mechanism uses a __________ to reduce the effort needed to lift a load.
Q6.Which of these is NOT an example of a simple lever mechanism?
Assessment exit quiz
6 Questions
Q1.Why do the pivot points on the levers of a lazy-tong linkage have to be in the same place on each lever?
Q2.Which two things do you need to use to safely make a hole for a pivot in cardboard?
Q3.What type of linkage is this?
Q4.What type of linkage is this?
Q5.What does a linkage connect together?
Q6.In a bell crank linkage, what connects the levers to the central 'bell' shaped piece?