What it shows
A motor turns a small pulley, a rubber band carries that rotation to a larger roller, and a loop of cloth belt stretched between two rollers moves objects along. It shows belt drives, friction grip and speed reduction through pulley sizes.
The science
The motor shaft turns fast but with little force. A small bottle cap on the shaft drives a larger roller through a rubber band, and because the roller is wider than the cap it turns more slowly, gaining turning force in exchange. The cloth belt is pulled tight over both rollers so friction makes it move with the driven roller; the second roller just turns freely. Anything placed on the top of the belt is carried along at the belt speed.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A 3 V DC toy motor
- Two cardboard tubes or thick pencils as rollers
- Two wooden skewers as axles
- A strip of cloth or an old sock cut into a loop as the belt
- A rubber band and a bottle cap pulley
- A 2 x AA battery holder with a switch and cells (3 V)
- A shoe box, hot glue and tape
Safety
For this project: An adult must use the hot glue gun and cut the skewers. Keep fingers out of the rollers while running.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
9 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Push a skewer through each cardboard tube and mount the two tubes at the ends of the shoe box, 20 cm apart, through holes in the sides.
Sew or tape the cloth strip into a loop just a little shorter than twice the roller spacing so it sits tight over both tubes.
Glue a bottle cap onto the motor shaft to make the small pulley.
Glue the motor to the box side so a rubber band can run from the cap to the end of one skewer, which has a second bottle cap glued on as the big pulley.
Loop the rubber band over both caps and check it is tight enough to grip but not so tight it stalls the motor.
Wire the motor to the battery holder through the switch.
Switch on: the belt moves. If it slips, tighten the cloth loop with a piece of tape on the inside.
Place a rubber, a coin and a small toy on the belt and time how long each takes to travel from end to end.
Swap the big pulley for a smaller cap and compare the belt speed.
What you should see
Objects placed at one end ride the belt to the other end at a steady speed, and a bigger driven pulley gives a slower, stronger belt.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why drive the roller through a rubber band instead of mounting it directly on the motor?
The band and pulleys slow the rotation down and increase the turning force.
2What stops the belt slipping on the roller?
Friction between the tight cloth and the roller surface.
3What happens if the two pulleys are the same size?
The roller turns at the same speed as the motor shaft, with no speed reduction.
4Where are conveyor belts used in India?
Airport baggage halls, cement plants and grain handling at mandis.
Take it further
Add a paper clip lever switch at the end so an arriving object stops the motor automatically.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Robotics
Motors, Gears and Motor Drivers
Make things move: DC motors, servos, steppers and how to drive them
Science projects
Best Out of Waste Science Projects
Working models from bottles, cardboard, CDs and old parts