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?