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Magnus effect car

Magnus effect car

Build a car driven by air currents, just like the one Jem drives in the TV show.

When a round object like a ball or tube spins fast, a small layer of air clings to the moving surface. If the object is moving, or if it is windy, this means the air on one side is moving faster than the air on the other. The difference in speed leads to unequal pressures, which pushes the object sideways.

The Magnus effect is responsible for footballs curving when kicked with spin. It gives golf balls longer flights when they’re struck right (and hook/slice when hit badly). It can give paintballs longer range, and it can make this model car drive along the ground powered by a side-wind.

Instructions below

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If the motor stops (or stalls) it could short-circuit the battery. Make sure you turn off the power or the wires will get hot hot hot!

Download and extra parts to make your kit look great! PrintOff these instructions and get making!
  1. Cut out all the printed partsGlue the main chassis template over the bottom half of the pet food box as shown

    1 Chassis

    Cut out all the printed parts. Glue the main chassis template over the bottom half of the pet food box as shown.

  2. Cut along the lines on the printed guide to create the chassis

    2 Cut along the lines on the printed guide to create the chassis.

  3. Find two straight skewers and poke them through the chassis where indicated

    3 Find two straight skewers and poke them through the chassis where indicated. Wiggle the skewers in the holes until they can rotate freely.

  4. Neatly cut the bottoms from the bottles

    4 Neatly cut the bottoms from the bottles.

  5. Drill holes as close to the centre of the bottle caps and the bottle bottoms as you can

    5 Drill holes as close to the centre of the bottle caps and the bottle bottoms as you can. Pick a drill size that will create a tight fit to the skewer axles.

  6. Poke a skewer, pointy-end first, through the centre of one of the wheels

    6 Poke a skewer, pointy-end first, through the centre of one of the wheels. Push it all the way through as shown.

  7. Thread the wheel and axle through the chassis holes and attach the other wheel

    7 Thread the wheel and axle through the chassis holes and attach the other wheel. Build up the second axle in the same way. Once complete, test that the wheels turn freely and the chassis rolls easily when pushed.

  8. 8 Motor

    Most motors have an adaptor on the shaft. You need to take this off, but save it for later.

  9. Glue the printed guide to a piece of cardboard from the pet-food box

    9 Glue the printed guide to a piece of cardboard from the pet-food box. Cut to shape and fold along dotted lines.

  10. Make a hole for the motor with a skewer where indicated

    10 Make a hole for the motor with a skewer where indicated. Check the motor fits neatly.

  11. Cut another hole for the switch

    11 Cut another hole for the switch. Draw around your switch to find the size, and place it where indicated on the guide.

  12. Hot-glue the switch and motor into place

    12 Hot-glue the switch and motor into place.

  13. 13 Work out what batteries your motor needs. Most are either 3 Volts or 12 Volts. Unsure? Try connecting 3V first (two AA batteries). If it doesn't turn or turns weakly, try connecting a 9V PP3 battery instead (the square type).

  14. Build the electrical circuit

    14 Build the electrical circuit. Solder is ideal for connections, but it’s hot, so take care!

    1. 1 Take one wire from the battery holder and wire it to the connector on the motor.
    2. 2 Take the other wire and wire it to one of the connectors on the switch. Some switches are arranged with 6 connectors. If yours is like this, use the middle left connector, and the bottom left connector.
    3. 3 Connect the other wire from the switch to the empty terminal on the motor.
  15. 15 Test your circuit works.

  16. Place the motor assembly in place in the chassis

    16 Place the motor assembly in place in the chassis. Don't glue it in as you may need to take it out to adjust it. Use sticky tape or blu-tac to hold it in place. Fix the battery in place in a similar way.

  17. Hot-glue the stiff cardboard tube into the chassis

    17 Magnus drum

    Hot-glue the stiff cardboard tube into the chassis as shown.

  18. Glue the remaining pattern to a piece of card

    18 Glue the remaining pattern to a piece of card. Cut to shape, fold and hot-glue into place.

  19. Take the adaptor that came off your motor and put it back on the shaft

    19 Take the adaptor that came off your motor and put it back on the shaft. This will act as a spacer to hold the drum up.

  20. Draw round your cardboard tube on another piece of card

    20 Draw round your cardboard tube on another piece of card. Cut it out and stick it into place as shown. Pierce the end.

  21. Create another wheel hub from a plastic bottle bottom, like you did for the wheels

    21 Create another wheel hub from a plastic bottle bottom, like you did for the wheels. Tape this to the other end of the drum to close it.

  22. Glue the card end of the drum to the motor shaft

    22 Glue the card end of the drum to the motor shaft. Pierce a skewer through the top support and fix it into the top of the drum. Trim to size.

  23. The Magnus Effect requires a bumpy surface to create the boundary-layer effect

    23 The Magnus Effect requires a bumpy surface to create the boundary-layer effect. Stick a sheet of patterned kitchen roll to the drum.

Let's play!

  • Put the car on a smooth level surface and turn it on. If the drum vibrates a lot, adjust it until it runs fast and smooth.

  • Set up the desk fan or hairdryer to the side of the car. Turn it on.

  • Turn on the car's Magnus drum. Wait a second or two for it to spin up, and the car should race off by itself!

Click here to play some more…

Try these cracking experiments...

  • Chase the car with the fan (from the side). It should keep running as long as there's a side wind.
  • Try different covers for the drum. What works best?
  • Try different speeds for the drum. You can make the motor faster or slower by adding/removing batteries. But don't go too far, or the motor might stop working.
Time
2 hours
Difficulty
Medium

Parental supervision required

Ingredients

Things you'll need to make this

  • Pet food 12x pouch box

    Make sure you find one that's in good condition.

  • Electric motor

    You can buy 3V toy motors cheaply in model shops and online.

  • Battery holder

    You can buy these, but they're fairly easy to scavenge too. Anything that has batteries has a battery holder in it: old TV remote control or bike lamp.

  • Wire

    You could recycle an old computer cable.

  • Kebab skewers

  • Small electrical switch

    You can buy these from electrical suppliers or DIY superstores.

  • Printed parts sheets

  • Stiff cardboard tube

    The centre of a roll of foil is perfect.

  • Light cardboard tube

    The middle of a kitchen-roll is ideal.

  • Four old or blank CDs

  • Small plastic bottles x 5

Download instructions

You'll also need these tools too:

  • Scissors
  • Hot glue gun and glue sticks
  • Craft knife
  • Soldering iron and solder
  • Drill or electric screwdriver with drill bits
  • Desktop fan or hairdryer

Competition

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