D. Structures and Mechanisms · Machines and Mechanisms

Design Challenge: Build a Machine That Lifts

A1.3 A1.4 A1.5 D2.2 D2.4 D2.5About 60 minutes

Learning goals

I can use the engineering design process to design, build, test and improve a machine.
I can use a pulley, a crank or gears to change the direction, speed or force of motion.
I can test my machine fairly and safely and record my results.
I can explain how my machine works using science words.

Words to know

engineering design process
The steps engineers use to solve problems: ask, plan, build, test, improve and share.

criteria
What your design must do to be successful.

constraints
Limits on your design, like the materials or time you have.

prototype
A first model you build to test your idea.

winch
A crank and axle that winds up a rope to pull or lift a load.

ratchet or brake
A part that stops a winch from unwinding when you let go.

The challenge

Your toy figure is stuck at the bottom of a "mine shaft" (the floor) and needs to be lifted up to the "surface" (a table or a box at least 40 cm high). Design and build a machine that lifts the toy safely.

Criteria (what it must do):

Lift a small load (a toy figure in a cup, or a cup with 10 coins) at least 40 cm.
Use at least one mechanism from this unit: a pulley, a crank and axle (winch), gears or a belt.
Change the direction or the force of the motion (for example, turn a crank to lift, or pull down to lift up).
Hold the load in place when you let go.

Constraints (limits): use only materials from home or the recycling bin; finish in about 45 minutes; a grown-up does any cutting or poking with sharp tools.

A homemade cardboard winch with a wooden dowel and crank handle lifts a toy figure in a small cup up to a table. — This model winch uses a crank and axle: turning the handle winds the string around the dowel and lifts the cup. Your design could use the same idea, or pulleys, gears or a belt. AI-generated image

Mechanism	What it does in your machine	Materials ideas
fixed pulley	changes the direction: pull down to lift up	thread spool on a pencil, taped to the top of a box or chair
movable pulley	reduces the force needed (about half)	second spool on a pencil, with the cup hanging from it
crank and axle (winch)	turning a crank winds string around an axle	pencil or dowel through a box, with a cardboard handle
bigger crank handle	more turning force with less effort	a longer cardboard handle
belt drive	a small pulley turns a big one: slower but stronger	jar lids and a large elastic band
brake	stops the load from falling	a clothespin clamped on the axle or string

Mechanisms you can use

Engineering design process

Ask (what's the problem?) → Plan (draw and label your design) → Build (make a prototype) → Test (does it meet the criteria?) → Improve (change one thing, test again) → Share (explain how it works).

The engineering design process. Engineers often go around the test → improve part many times before a design meets every criterion and is ready to share.

Worked example

Let's follow one engineer's design

Priya designs a winch with a pulley to lift a cup with 10 coins 40 cm.

Ask: How can I lift the cup 40 cm by turning a crank?
Plan: A shoebox on the floor holds a pencil axle through two holes. A cardboard crank handle is taped to one end of the pencil. String is taped to the middle of the pencil. The string goes up to a spool pulley taped to the edge of the table, over it, and down to the cup. She labels each part and its purpose.
Build: A grown-up pokes the holes. Priya builds it.
Test 1: She turns the crank. The string winds up and the cup rises. But the cup falls when she lets go, and turning is hard. Criterion 4 is not met.
Improve 1: She clips a clothespin onto the pencil against the box as a brake. Now the cup stays up.
Improve 2: She makes the crank handle longer (from 5 cm to 10 cm). Turning is easier: a bigger wheel gives more turning force. She changed only one thing at a time and tested again.
Share: "Turning the crank (rotary motion) winds the string on the axle. The pulley changes the direction, so the string pulls up on the cup (linear motion). The longer handle needs less force, but my hand moves farther."

Priya's machine met all 4 criteria after 2 improvements. Every change she made used a science idea from the unit.

A sketch of Priya's design. Turning the crank winds string onto the pencil axle. The string runs up and over the spool pulley, so the cup is pulled up 40 cm to the table.

Test	What I changed	Lifted 40 cm?	Held the load?	Easy to turn? (1 = hard, 3 = easy)
1	first prototype	yes	no	1
2	added clothespin brake	yes	yes	1
3	longer crank handle	yes	yes	3

Priya's test record

Just for fun

A prototype that works perfectly on the very first try is like a unicorn: everybody has heard of one, but nobody has ever seen one. Testing and improving is where the real engineering fun happens!

Hands-on activity

Build your lifting machine

You need (choose what fits your plan): a shoebox or cereal box, pencils or wooden dowels, empty thread spools, string (about 2 m), a paper or plastic cup, coins or a small toy for the load, cardboard, tape, glue, clothespins, jar lids, large elastic bands, a ruler, paper and pencil.

Ask: read the criteria and constraints again.
Plan: draw your machine. Label each part and write its purpose. Show the input and the output with arrows.
Build: build your prototype. A grown-up does all cutting and poking.
Test: try to lift the load 40 cm. Record the results in a table like Priya's.
Improve: change one thing at a time and test again. Try at least 2 improvements.
Share: show your machine to your family. Explain how it changes the kind of motion, the direction or the force, using words like crank, axle, pulley, rotary, linear and trade-off.

What to look for: a labelled plan, a working prototype that lifts the load 40 cm and holds it, a test record, at least one improvement based on testing, and an explanation using science words.

Safety: light loads only; never stand or put your face under the hanging load; keep string away from necks; a grown-up uses scissors, knives and skewers; keep coins away from small children (choking).

Your turn

Name the six steps of the engineering design process in order.

What are criteria?

What are constraints?

What is a winch?

Priya's cup fell when she let go. What did she add to fix it?

Why did a longer crank handle make Priya's winch easier to turn?

Why should you change only one thing at a time when you improve a design?

More practice: warm-up

What is a prototype?

Which mechanism lets you pull down to lift up?

Which mechanism reduces the force needed to lift by about half?

In a winch, what kind of motion does the crank have?

Why must no one stand under the hanging load?

More practice: on your own

In Priya's machine, where does motion change from rotary to linear?

Your machine lifts the load, but the string keeps slipping off the spool pulley. Suggest two improvements.

How could you make your machine lift a heavier load with the same effort?

Write a sentence that shares how a pulley-and-winch machine works, using three science words.

Your test record shows: Test 1 lifted 25 cm; Test 2 (taller pulley) lifted 40 cm. What did the improvement fix?

Challenge

Add a second mechanism so your crank turns the winch axle more slowly but with more turning force. What could you add and how would it work?

A classmate's machine uses 1 fixed pulley. Yours uses 1 fixed pulley and 1 movable pulley. Both lift the same cup 40 cm. Compare the force needed and the string pulled.

A real elevator uses steel cables, big pulley wheels, a motor and brakes. Name two ways it is like your model and one way it is different.

Check your understanding

Quiz

What comes right after test in the engineering design process?

What must your design do to be successful?

Which part stops a winch from unwinding?

A longer crank handle makes a winch...

When improving a design, you should change...

Which is a safety rule for this challenge?

For parents and teachers

Big idea (A1.3, A1.4, A1.5, with D2.2, D2.4, D2.5): This challenge brings the unit together. Your child plans, builds, tests and improves a lifting machine using pulleys, a winch, belts or gears, then explains it with science words.

How to help: Resist fixing the design for your child. Ask questions instead: "Which criterion isn't met yet? What could you change? What will you keep the same?" Celebrate failures that lead to improvements.

Common difficulties:

Changing many things at once. Encourage one change per test.
Skipping the plan. A labelled drawing first saves time.
Explaining without science words. Prompt: "What kind of motion? Where does the direction change?"

Safety: You handle cutting, poking holes and anything sharp. Use light loads, keep string away from necks and nobody stands under the load. Coins are a choking hazard for small children.