Introduction: Cotton Reel Tanks
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
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 ?
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.
13 years ago on Introduction
Enjoy the video!
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.
Reply 13 years ago on Introduction
lol how about an unused match!
14 years ago on Introduction
Ya like a chostick a thin one though
14 years ago on Introduction
Mine just jumps around and throws the pencil at people! Whats wrong?
Reply 14 years ago on Introduction
theres nothing wrong you just made a sweet tank wepon that can poke peoples eyes out :P
Reply 14 years ago on Introduction
Try not winding it as tight or slackening the band.
15 years ago on Introduction
Neat, i think i'll make this with my son and have some fun.
15 years ago on Introduction
Nice! But I dont think that the pen is the best thing to use here. A small lightweight stick should be ideal.