Step 1: The Nozzle
thin, bendable sheet of plastic or any other material that can be used to build a cone
two boards of MDF or any other sturdy material
For the nozzle we chose an arc with a radius of 61cm made of a thin and bendable sheet of plastic. The angle depends on the size of the stand for the nozzle but it is helpful to have sufficient material overlapping as this makes the procedure of taping/gluing the cone much easier. In our case, we decided to use tape as it was quicker to apply and seemed to be stable enough to keep the cone in form.
The stand for the nozzle was made out of 1.8cm thick boards of MDF. The dimensions we used can be taken from the photo below but can also be modified. If choosing different dimensions it is important to note the following:
- the greater the inlet area, the better as it catches more wind
- the smaller the outlet area in comparison to the inlet area, the greater is the difference in speed (the outlet velocity is greater than the inlet velocity) which leads to an increase in kinetic energy the rotor is able to catch
- the diameter of the outlet must be slightly bigger than the rotor diameter ensuring an optimum distribution of the wind at the contact surface of the rotor blades including the tips
For a better fit of the cone into the boards it is helpful to sand the edges of the circles at the appropriate angle.
The next step is slotting the boards onto the boards and gluing it. If the outlet seems to be too small, it will be easiest to trim the nozzle at this point.
Step 2: The Blade
Solidworks (Cad software)
The blades were drawn in Solidworks. The co-ordinates of a NACA 1412 airfoil were used (co-ordinates provided by www.worldofkrauss.com). This specific airfoil was chosen due to its use in horizontal axis wind turbines already. The airfoil was then scaled to 45mm and extruded to 140mm, as used in our previous prototype testing. Using the flex feature on Solidworks, we curved the airfoil to 22.5°, this was justified by using an equation involving the length of the blade and width in calculating the optimum angle for these specific dimensions. A triangular piece was drawn to the bottom of the blade which will be used to screw holes and attach the blade to the shaft. Furthermore we created a lip at the blade attachment to further lock the blade with the shaft.
The blade was 3D printed using a 3D rapid printer, it was then sanded and painted in order for a silicon mold of the blade to be made. Using the mold, three more blades were cast using resin. This method of duplicating the blade was cheaper than 3D printing all of them.
Two holes were screwed on each triangular attachment of the blades, which correspond to holes in the shaft. The blades are then screwed in place on the shaft and the nose ontop.
Step 3: The Gears & Generator
Threaded steel rod
Thin steel sheet
The main block is cut to dimensions of 150x5x4mm on the band saw, but the rest is done using CAD to ensure accuracy. Having placed the Perspex into the CAD machine, it is programmed to cut a hole dead center of 36mm diameter, for the motor. Around this 4 holes are cut for the securing screws.
The block is now rotated by 90 degrees. A hole is made at each end for the steel rods to pass through. These are down the center of the block at a distance of 25mm from the end. We decided to mill these holes, as they didn’t need to be so accurate.
Now that the block has been made, it can be sanded down to create a nice finish.
The motor is secured into place using a metal plate. This is a square cut from steel to fit on the front of the sliding block. A hole is drilled for the motor to fit through and 2 holes are drilled either side for the attachment to the motor. A hole is also drilled in each corner for attachment to the Perspex block.
This is another block of Perspex cut to dimensions of 15x4x2.5mm. At the same positions as the vertical holes in the previous block, 2 holes are drilled, but only half way through. These holes however will be threaded so as to hold the steel rods secure. Holes are also drilled on the underside so that the block can be screwed down to the base.
The threaded steel rod is simply cut to size. Now it can be assembled as shown in the third image.
Step 4: The Stand & Shaft
Sheet of plastic
To make the stand we drilled two holes into the face of a 40x30x276 perspex block. The first hole goes straight through the perspex block and the second hole goes only 7mm deep. The dimensions are given in the diagram.
The shaft was then made in a lathe to the dimensions shown in this diagram.
The M5 part of the shaft was threaded so that the nose can be screwed onto it with some superglue in the thread.
The 22.5mm diameter, 7mm deep hole houses the bearing. The shaft then slots into the bearing. We used a 22mm bearing.
You should secure your large gear to the 4mm part of the shaft. We used a 4:1 gear ratio from the shaft to the generator.
To secure the stand to your MDF board you could drill two holes through the board and perspex and then thread the perspex holes and then use a nut to hold them in place. You would need to countersink the holes on the underside of the board.
We just used superglue. Using superglue was much easier to use and to be able to get the gears lined up correctly. To ensure that it was secure, we super glued more perspex blocks to the MDF board and to the base of the perspex stand and to the base perspex block at the base of the generator.
The most important part of securing the stand is making sure that the gear on the shaft lines up perfectly with the gear on the generator generator.
The nose for the wind turbine could be made of aluminium in a lathe to the dimensions shown on this diagram. For our turbine, we chose to use a wooden nose made on the lathe and vacuum covered it for a smoother surface.
After the blades have been screwed on you should screw on the nose with some superglue on the inner thread.