An old one but a good one. Your parents or grandparents will remember making this very simple machine which will give you hours of fun. You only need everyday household equipment and the temporary use of an adult.
Pass this information to your friends and you can have Cotton Reel Tractor Races. Don’t forget to send us your photos – we would love to see your contraptions!
What you will need
1. One Cotton Reel (instructions are for the modern plastic “hollow” type. Modify for solid designs)
2. One rubber/elastic band about 9 cm (18cm circumference)
3. One paper clip
4. One candle (2 to 3 cm diameter)
5. One match or toothpick
6. One adult with a sharp knife – this is not a optional extra
How to do it
1. Take your paper clip and open it out so that one end is straight and the other end has a hook on it.
2. Take the rubber band and push it through one of the outer holes (shaped like a Diarylea cheese with the end nibbled off).
3. Push hook end of the paper clip into an adjoining hole and snag the end of the rubber band.
4. Pull the rubber band end out so you have two loops outside the cotton reel.
5. Pass one loop through the other and pull tight.
6. Take the long end of the rubber band and poke it through the centre of the cotton reel.
7. Take the adult and get them to cut about 1 cm to 1.5 cm from the end of a domestic candle to create a washer.
8. Very carefully drill or otherwise create a 3 mm to 5 mm hole in the centre of the candle washer
9. If your adult splits the candle go back to number 7. If it happens more than twice, change the adult.
10. Pass the end of the rubber band through the candle washer.
11. Place the match in the loop and wind about 50 times.
12. You can experiment with more or less winds but if you go for more, make sure you have a spare rubber band.
13. The rubber band should be close to one end of the match.
14. For superior tractors try cutting a groove in the candle washer to locate the match.
What to do?
- Place the whole assembly on a flat surface then stand back and watch in amazement.
- If the candle washer is not smooth it will not sit flat on the cotton reel and will tend to slip. This adds an interesting erratic movement to the tractor.
- Decorate your tractor. It won’t go faster but it will look even cooler.
What is happening?
Einstein taught us that energy cannot be destroyed it can only be changed. The energy you exert to wind up the tractor remains as stored mechanical energy until it is transformed into movement as the reel moves.