What it shows
An unbalanced motor on a plastic cup makes it wobble on three marker legs, and the wobble is traced out as a looping drawing. The pattern depends on the weight, the speed and how far apart the legs are.
The science
The motor spins a weight that sits on one side of the shaft, so every turn flings the cup a little in a changing direction. The three markers act as legs that are stiff enough to hold the cup up but let it hop and skid. Each tiny hop moves the pen tips a few millimetres, and because the direction of the push rotates with the shaft, the path curls into loops and spirals. Changing the weight changes the force, and changing the leg spacing changes how easily the cup tips, which changes the drawing.
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 plastic cup or an empty yogurt tub
- Three sketch pens or markers
- A 3 V DC toy motor with a glue blob or a cork piece fixed off centre on the shaft
- A 2 x AA battery holder with a switch and cells (3 V)
- Rubber bands and tape
- A large sheet of paper
Safety
For this project: An adult must use the hot glue gun. Keep marker caps and small parts away from toddlers.
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
8 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.
Fix a piece of cork or a glue blob onto one side of the motor shaft so it is clearly unbalanced.
Turn the cup upside down and strap three markers around it with rubber bands, tips down, spread evenly.
Adjust the markers so all three tips touch the table and the cup stands level.
Tape the motor onto the top of the cup with the weighted shaft free to spin over the edge.
Tape the battery holder on top and connect its wires to the motor terminals.
Uncap the markers, place the bot on the paper and switch on.
Let it wander for a minute, then try a bigger weight, or move the markers closer together, and compare drawings.
Label each drawing with the weight and leg spacing used.
What you should see
The bot leaves looping, spiral patterns on the paper, and changing the weight or leg spacing visibly changes the pattern.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What makes the cup move?
The off-centre weight shakes the motor and the cup with it, hundreds of times a second.
2Why three legs rather than four?
Three points always touch a flat surface, so the bot never rocks on a raised leg.
3Why does a heavier weight make bigger loops?
It produces a bigger unbalanced force, so each hop moves the bot further.
4What energy changes happen?
Chemical energy in the cells becomes electrical, then kinetic energy of the motor and cup.
Take it further
Add a second motor spinning the opposite way and see whether the drawings become straighter or more tangled.
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
Science projects
Best Out of Waste Science Projects
Working models from bottles, cardboard, CDs and old parts
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