An oldie but goodie, cotton reel tanks are great fun. Add your own tweaks and race them!

Step 1: What You Need

Erm... what's in the picture:

- a cotton reel
- a rubber band
- a pencil
- a match

plus sellotape, scissors etc

(For advanced models you can add extra stuff - but this will do it)

Step 2: Next...

Thread the rubber band through the cotton reel.

If the rubber band is much more than the length of the cotton reel, shorten it by tying a knot in one end (see pic in next step).

Step 3: And Then...

Break the matchstick in half. Put one end of the rubber band over one matchstick half. Sellotape the rubber band and the piece of matchstick securely to the end of cotton reel, making sure it doesn't stick out.

Step 4: Now...

At the other end of the reel, stick the pencil through the rubber band. It should be not too tight, not too loose (experiment!).

Step 5: And Then

Wind up the tank by winding the pencil with your finger

Step 6: ... and Titivate

Let the tank go and it should run across your desk.

You want to minimise friction between pencil and reel. You might need to add a spacer like this (cut from a cork) - and maybe some washers cut from waste plastic (I used a box that had had fruit in).

Step 7: Advanced Model

For the pro model, use a section of candle as the spacer/washer, and wrap the 'wheels' in more rubber bands.

Use your imagination: how about a soap washer? Would a longer pencil work better? How about linking two tanks together so they don't run in circles?

Have fun.

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11 Comments

eemke

Question 4 years ago on Step 7

I made these with a lot of kids but they didn't work , well one did work very good and a few did work very slow , what can I do to make them work better ?

costajules

13 years ago on Introduction

If it just jumps around and throws the pencil at people, it is because there is nothing to limit the speed of the rubber band unwinding. These things need something to provide a delicate amount of friction. A washer carefully made of candle wax as marcusmorris says works nicely. Normal washers don't, and I can't see cork ones working great either.

marcusmorris

13 years ago on Introduction

In my day we used candle wax for the escapement mechanism - nice, slow and controlled. Also, we cut notches in the rims of the reels so the tanks could climb obstacles. We used penknives for this purpose. Every schoolboy had a penknife back then (indeed the UK Scout movement insisted on it) but perhaps it is more prudent to suggest the use of a file or a junior hacksaw in these modern times where the possession of anything vaguely sharp is considered by the authorities to be highly anti-social and the slightest bloodying of a finger is sufficient reason to take a knife manufacturer to court for failing to print an appropriate warning on the item.
Enjoy the video!

yeracs87

14 years ago on Introduction

Made them as a kid 40 years ago but called them spool bugs. Try using an already used wooden match instead of the pencil. Less weight goes easier around on the floor.