This tutorial shows how you can make your
own fan that is powered by hot water. It uses a muscle wire made from nitinol (nickel titanium alloy). A muscle wire can be deformed when it is cold, but when it is heated it reverts back to its memorized shape. In this case the wire reverts back to completely straight, as it hasn’t been set to any other shape. This principle makes it possible to propel a little engine. The moment the wire reaches the water it wants to expand to a straight wire, however it is constrained by the connection. The tension on the wire pulls on the pulleys which start to rotate.
We added a small rotor to the upper pulley so the “engine” becomes a fan.
In the following steps we will explain how you can make this fan!
You will need:
- A rotor blade (from for example a drone or small fan)
- 2 pulleys (made on a lathe, turning machine): diameter of 50 mm and 30 mm
- 2 axis, as long as the combined thickness of the components, diameter same as inner diameter of the nylon bearings, in our case this was 4mm.
- 4 star-locks
- Sheet of plastic
- Nitinol muscle wire
- Two-component glue
- Thin metal wire
- 2 nylon bearings (fitting the inner diameter of the centre hole of the pulleys) We had a 6mm hole and thus our bearings had an outer diameter of 6mm and an inner diameter of 4mm
- Cup of boiling hot water
Step 1: The Pulley
The pulleys are gears from which the teeth
were removed using the turning machine. Then with a convex chisel, the edge of the disc can be hollowed so a lining for the wire appears.
One disc should be made with a diameter of 50mm and the smaller one with a diameter of 30mm.
Glue the rotor blade to the bigger pulley.
Or if the pulley is from nylon, double sided tape will do the trick.
If the pulley is made from a plastic sheet,
then also drill a hole in the center. This should be as big as the outer diameter as the nylon bearings.
The pulleys could be bought as well
Step 2: Main Structure
From the plastic sheet, you want to saw a
strip of about 30mm wide and 120mm long. Sand the edges for a nice finishing.
Drill two holes, same diameter as the inner diameter of the bearings. The holes should be located around 15mm off of the edges of the plastic strip.
Step 3: The Axis
Find a metal rod that has the same diameter
as the inner diameter of the nylon bearings. To determine the length of the axis, measure for the small pulley the thickness of the pulley and the plastic sheet thickness used for the structure. For the longer axis you also need to measure the thickness of the rotor. Add up the numbers and add 10mm for the starlocks and some freedom for the components. Saw the axis on the right lengths and sand the edges.
Step 4: Assembling
Now, it is time to assemble the parts. Put a starlock on one side of the axis and then put it through the hole in the plastic strip. Now, put the pulley on the axis and close it with another starlock. Don’t put it too tight to the pulley. Do this for both pulleys.
Step 5: The Wire
Measure Length: Put the wire around the pulleys loosely, it does not have to be very tight as you want to be able to take it off of the pulleys. Measure the length and add a little overlap where the wire can be connected.
Cut the wire to the right length.
There are two options to connect the wire ends:
1) Soldering: Sand the ends of the wire well so that the oxide layer is removed, you will see the metal shine. Secure the wire in a workbench and solder the ends together
2) Wrap and Glue: Secure the wire in a workbench and wrap a thin silver wire around the overlapping area. Add some two-component glue to the area and let dry
Make sure the connection between the two ends of the wire is as fluent as possible, otherwise the engine may jam at this point.
Step 6: See It Spin!
Time to test the nitinol engine fan!
Take the wire and put it around the pulleys.
Boil water and put this in a cup, hold the fan in such a way that the wire just touches the water
and watch it spin!
To make it work better, we also used compressed air, which functioned a little bit like cold spray. This makes the temperature difference between the air and the water bigger, so the response of the wire is stronger.