Note: The following are instructions on how to build a miniature, educational wind turbine. This device has been specifically designed for use in a custom built wind tunnel, but would work anywhere with concentrated wind flow.
Medium Density Fibreboard (both 10mm and 20mm thicknesses)
Small block of aluminium
Silicon moulding equipment
5mm steel bar
4x 8mm bearings
5 x 5mm grub screw
2 x 40mm diameter plantpot (optional)
Steel Block (for bearing housing)
Hot glue gun
Note: some steps require access to expensive equipment (3D printer, lathe etc.).
Step 1: Blades
The first step in making the turbine blades is to model them in your preferred CAD software. For maximum efficiency a calculated airfoil should be used. The Team found http://www.worldofkrauss.com to be a useful tool in selecting these. in this case the MH32 was chosen due to its effectiveness in direct wind flow.
The CAD model of the blade was then rapid prototyped in a 3D printer ( minimum resolution 0.5mm) . Be careful to ensure that the blade has an appropriate twist, dependent on wind strength/direction.
In order to connect the blades to the hub (see next step), an 8mm cylindrical extension was added to the end of the airfoil. This saves time later when attaching the blades.
The CNC model was then used to create a mould from silicon. using this mould, the remaining blades were cast using a urethane mix.
Step 2: Base
The base was constructed mainly from mdf of varying thicknesses. (Design of the base should be altered to fit the wind tunnel). The team wanted to make the most of the small space available, and so long garden plantpots were used to make the nozzle/diffuser. The purpose of these is to concentrate airflow and reduce turbulence respectively.
The supports for the plantpot were cut from 10mm thick mdf. The circular shape was cut using a bandsaw and then sanded to a smooth finish.
Next, the supports for the blades, bearing housing and motor were cut. These were fastened to a small "spine" fitted a thick mdf base plate using a cross halving joint.
Step 3: Nosecone and Hub
To finish off the business end of the turbine, a small nosecone was machined from an aluminium bar. An M8 thread was drilled into the rear of this component, so that the shaft could run continuously from the front directly to the motor. This also acts as a fastner for the blades and bearing housing.
Next, a hub was also machined from aluminium. 3 grub screws were positioned 120 degrees apart and perpendicular to the 8mm holes for the blades. at this point, some 3mm steel rods wre inserted into the blade/hub connection in order to strengthen the blades.
Step 4: Gearing and Motor
A belt drive was selected for the gearing system, due to the low tolerance for movement/allignment and the ease of implementation. two pulleys were machined from mdf using a wood lathe. after some testing, it was found that the best ratio was 2:1. A pulley was mounted on the end of the threaded shaft which ran through the bearing housing, and secured with a nut and bolt.
The small turntable belt than was the ran around the second pulley, which was mounted on a smaller shaft connected to the motor.
After some testing we discovered that the belt was vibrating quite substantially due to the wind. we therefore attached two small acrylic wind blockers, which significantly improved performance.
The Turbine performed well and placed 4th overall in a competition with various other designs, generating 12V.