The model is driven by a motor which has been geared down to a suitable speed by the use of a simple pulley system. Children will use a range of components and practice skills such as cutting, joining and finishing accurately. Depending on available resources, children might work together in small groups, or it could be a whole-class project.
What you’ll need
Components and materials:
You will either need all of the items listed below or, why not buy the full Fairgrounds D&T class kit. A cross-curricular STEM kit for thirty pupils that builds on previous knowledge of circuits, structures and more. Created by Caroline Alliston, a mechanical engineer and author of the “Technology For Fun” book series this kit allows thirty models to be made however it is also possible to work in pairs, groups or as a whole class. Before starting this activity why not research the history of fairgrounds or a local event for example the Goose Fair in Nottingham to further inspire your pupils!
- Battery holder
- AA zinc chloride cell (do not use alkaline or rechargeable cells – if you accidentally short circuit your battery these will get hot)
- Toggle switch
- Motor mount
- 3 crocodile leads
- Plastic pulley 50 mm diameter
- Rubber band ~ 1.5mm x 1.5mm x 10cm long
- Wheel with 5mm diameter hole
- 2 wheels with 6mm diameter hole
- Focused task box (as in kit – or use a suitably sized box and add holes)
- 15 giant lolly sticks
- 2 cotton reels
- Several cable ties 30cm long
- Wooden dowel 5mm diameter x 120cm long (if you are short of 5 mm dowel you can use a 27cm length for the central shaft and use garden cane or wooden skewers for the outer poles)
- Square section wood 8mm x 50cm long
- Sheet of 3 mm thick Corriflute 25cm wide x 50cm long
Passengers: you could use small soft toys or make these from pine cones with stick-on eyes
- Pencil sharpener
- Blu Tack
- Pair of compasses (or a plate about 24 – 25cm in diameter)
- Large pair of scissors
- Junior hacksaw and vice
- Low-melt temperature glue gun
- Secateurs (optional – to be used by adults only)
Make the circuit shown below and check that the motor shaft goes round when you switch on. Be careful not to short circuit your battery (i.e. connect the wires from your battery directly together) – they must go via the motor. Ensure the switch is in the off position.
Fold up the focused task box and glue the seam to make a cardboard base. Cut a central shaft of 27cm long from the 5mm dowel using either the hacksaw and vice or the secateurs. Use the pencil sharpener to sharpen both ends slightly; don’t make a sharp point. Push it through the central holes and use this as a guide to attach the wheels with 6mm hole. Glue these, one each side of the base.
Remove the shaft from the base. Cut two 14cm lengths of square section wood and two 8.5cm lengths. Smooth the ends using sandpaper. Make a rectangular frame out of the wood and glue it to the base as shown. Take three giant lolly sticks and glue them onto the frame, with one stick either side and one in the middle. Turn the base over.
Clip the motor into the motor mount and stick it to the base so that the motor shaft is sticking up above the level of the base as shown. Attach it firmly to the base with a cable tie. If you fit the motor near a corner it is easier to get the cable tie around it. If your cable ties don’t fit through the holes in the base you can enlarge the holes using a pencil. Glue on the switch where it may be easily accessed. Glue on the battery. Fold the wires neatly round the outside of the base so they don’t get in the way of the rotating parts and attach them using cable ties. Switch on to check that the motor shaft still rotates, then switch off.
Make two pencil marks on the shaft, 5cm and 6cm from the end. Push a wheel with a 5mm hole along the shaft until the 6cm mark is visible (as shown). Push the 50mm pulley along the shaft until the 5cm mark is visible. The wheel and pulley can both be a very tight fit; you can clamp the rod in a vice just below the 6cm mark and use your weight to push them down the shaft.
Hold the rubber band over the pulley and the wheel. Slide the end of the shaft down through the central holes in the base until it rests on the giant lolly stick. Stretch the rubber band over the motor shaft and switch on. Check that the shaft rotates and the rubber band doesn’t come off the end of the motor shaft when running. If it does, slide the motor up slightly and try again. The rubber band should run roughly in the middle of the motor shaft.
Use a compass, or draw round a plate, to mark a circle of about 24 – 25cm diameter on the Corriflute (at the edge, not the middle of the sheet) and cut it out. Use the ruler and pencil to mark a line passing through the centre. Use the protractor to mark out 6 lines at 60° as shown. Measure and mark each line 2cm from the edge. Make sure the pencil is sharp, and use it to make holes in the centre and the 6 positions you have marked. The holes should be big enough to push the end of the wooden rod into; it needs to be a tight fit. If you are using garden cane or wooden skewers for the outer poles, make sure the holes just fit these.
Use your first disc as a template to mark out a second one. Place the disc on the remaining Corriflute, draw round it and pierce the holes using a pencil. Use the pencil to enlarge the holes so that the wooden rod (or garden cane or skewer) fits tightly. Cut six pieces of rod 15cm long and sharpen one end slightly. Slide the pointed end through the six outer holes in both discs as shown, so that there is 1cm protruding at either end.
Slide the central shaft upwards out of the cardboard base (without losing the rubber band). Push the disc assembly onto the shaft and glue it to the top of the wheel. Hold the rubber band onto the pulley, slide the shaft back through the central holes in the base and stretch the rubber band over the motor shaft. Switch on to try out your merry-go-round. Stick two cotton reels onto the top, then glue on the lolly sticks as shown. Populate your ride with small lightweight soft toys, plastic figures, pine cones with stick-on eyes etc.
You could stick a piece of brightly coloured insulating tape onto the fairground ride (near the middle so that you can see it as it rotates) and time 10 revolutions, to work out the number of revolutions per minute (rpm). You could estimate the diameter of the circle travelled by the passengers, work out the circumference, multiply by the rpm, and convert your units into miles per hour to find out how fast they are travelling.
With thanks to Caroline Alliston, a mechanical engineer and author of the “Technology For Fun” book series for writing this post.