Many machines convert a reciprocating movement into a rotating one. The combustion engine is a well-known application of this mechanism, used, for example, in a car engine. In this project, children are introduced to the crankshaft mechanism. They will construct an working mechanism to flap the wings of their own made ornithopter. This activity is suitable for children of 9 years and up.
The word Ornithopter is derived from the Greek words Ornithos (bird) and pteron (wing). We depart from the questions ’Which animals are able to fly?’; ’What flying machine do we know?’ and ’What is the difference between an aeroplane and a bird?’. Children can be asked this while they look at images of a bird, a plane and a flying ornithopter. A Canadian team managed to build an ornithopter, propelled by humans. Their project is presented on Youtube.
The piston and crankshaft mechanism
The crankshaft mechanism is widely used in machines to convert a reciprocating motion into a circular motion, or visa versa. For example, the combustion engine burns fuel and releases energy in the form of high pressure, which in turn causes the piston to move up and down. This mechanism can be used to rotate the wheels of a car or the rotors of a propeller. Additional clarifying animations and more information are available on wikipedia and the NASA website:
Initially children need to be introduced to the terminology used: crank, lever and shaft. Encourage them to consider where they have encountered the crank mechanism before. Many will recognise it on the wheels of a locomotive, like Thomas the tank engine and the Hogwarts Express in Harry Potter.
Build your own ornithopter
The best way to become acquainted with the crankshaft principle is to build one yourself. This can be achieved with cheap materials, like a Cornflakes box, steel wire en straws. Some cellotape and arts and crafts materials can also be useful. By using recycled materials, this Dwengo activity is free.
The lever and crank (1x) and the crank and wing supports (2x) are made out of wire. Use steel wire that is stiff enough yet still pliable (wire for gardening is suitable).
A crafts cutter is needed to cut wire. Scissors are not appropriate for this use: The steel wire is too hard to cut while the scissors will be damaged. Remember to ask children to bring a crafts cutter from home, if they have one.
Download the Dwengo Ornithopter template and print it on A4.
Our ornithopter is a cardboard bird with two wings. Both the body and wings are cut out of thin cardboard (e.g. cornflakes box). In order to stimulate the children’s creativity, pupils can be encouraged to design their own bird. Ensure that the base is 4 cm by 6 cm, as on the Dwengo template.
Each child receives 1m steel wire. They are instructed to cut the wire and shape it to fit the printed Dwengo template.
Once all the parts are prepared, the ornithopter is ready for construction. This means each child has: 2 cardboard wings, the cardboard bird with base, one steel wire lever and crank, and two wire cranks with wing supports.
Assembly Now make the two conductors for the cranks and wing support from a drinking straw. These are attached to both sides of the cardboard bird. The lever with crank is fitted to the bottom of the base.
The two cranks with wing support are slid into place in the conductors (straws) that were previously attached to the bird. Then bend the steel wires so that they carry the cardboard wings, which can now be added. If everything has gone according to plan, your mechanism will now look like the image below:
Determining the length of the shafts
In order to allow the wings to move up and down, the shafts are connected to the cranks. The length of the shafts is key to success: if they are too short, the mechanism will not work! Let the children determine the ideal length. Some will use the trial and error method, while others will reason according to their foreseen wing positions.
It is useful for the children to study each other’s ornithopters in group and contemplate questions such as ‘whose wings work in a synchronous way’ or ‘how was the length of the shafts determined’.
Let it fly!