Mechanical Advantage — The EV3 Pulley Crane
Source: Stemoto Original
Students construct a motorized crane using EV3 motors and laser-cut gear trains. They test single vs. compound pulley setups to measure how gear ratios reduce the motor effort needed to lift a physical weight.
Categorisation
Props & Materials Required
- •LEGO MINDSTORMS EV3 kit
- •Laser-cut pulley gears
- •String or fishing line
- •Small weights (washers, coins, or LEGO bricks)
- •Spring scale or rubber band for measuring force
Step-by-Step Instructions
Build the Crane Frame
Use LEGO beams and the EV3 motor to construct a tall crane arm. The motor will power the winch that lifts the load.
Single Pulley Test
Attach a single pulley at the top of the crane. Thread a string through it and tie a weight to the end. Lift the weight using the motor. Measure the effort needed (using a rubber band stretch or spring scale).
Compound Pulley Test
Now add a second pulley to create a compound system. Lift the same weight again. Is it easier? Measure the difference. The child discovers that more pulleys = less effort, but more string to pull!
Gear Ratio Experiment
Swap the laser-cut gears to change the gear ratio driving the motor. A larger gear driving a smaller one = faster but weaker. A smaller gear driving a larger one = slower but stronger.
Record and Compare
Create a data table: Pulley Type | Weight Lifted | Effort Required | Distance Pulled. Discuss the trade-offs and connect to real-world cranes and construction.
Why It Works & Notes
Physics in action — children physically feel the difference between lifting a weight directly vs. through a pulley system. They discover that mechanical advantage means trading distance for force, a concept that underpins all engineering from cranes to bicycles.
NEP Alignment: Physics in action, practical understanding of mechanical force and work. Curriculum Mapping: Science (Force, Work, Energy, Simple Machines). Target Level: Class 4 & 5.