fan powered mobiles
This is a very simple mobile made by taping a bearing made from a bent paper-clip to the badge on the middle of a desk fan
A hole is made through the middle of a drinking straw and it is threaded onto the wire sticking out from the middle of the fan, it is prevented from coming off with a small tab of sellotape. Streamers can be attached to the ends.
Link to movie
It works because the stream of air from a desk fan whirls round & round, I think this is because the paddles are usually made a very inefficient shape. Much more elaborate versions can be made
This one has bearings & propellors in place of the streamers, the propellors are made just like the middle rotor but with paper aerofoils taped to the straws, they also have streamers in the middle.
Link to movie
This next one is a bit like the first one except it has pivoted drinking straws in place of streamers
Because they are constrained to swing round one axis it creates a sort of baffling mechanical movement. Here is a detail of the attachment of the straws to the central straw
Link to movie
You can then put streamers at the ends of the arms, but I found this would only work with a large desk fan
Link to movie
robotic cheerleader
This is a suspended mobile that incorporates a battery-operated fan: the fan at one end of the horizontal arm is balanced by two AA batteries at the other end
movie
It has two additional arms, one above the horizontal arm and one below
All the arms are attached to a central tube made of bendy drinking straws which is pulled round a central axle by the fan arm
The central axle is made of bent wire and doesn't rotate. So it makes the upper and lower arms wobble as they go round
movie
To make the flexing joints strong enough I had to use three layers of bendy straws, one on top of the other
You have to arrange the arms & streamers in such a way that they don't bash into each other, the streamers mustn't tangle or get sucked into the fan
movie
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my email is davidvwilliamson@hotmail.com