Introduction: Miniature Wind Turbine
It should be noted that this turbine is designed as a prototype for use in a wind tunnel. The wind speed in the tunnel is much greater than average wind speed in most areas. If you wish to build this turbine for use outside, we recommend that you use a lower ratio gearbox.
For this project you will need:
Materials / Components
-An inexpensive cordless drill
-A DC brushed electric motor
-20mm thick MDF
-30-40mm diameter wooden dowel
-Steel shim / thin steel sheet
-Brass shaft coupling
-1mm thick polystyrene sheet
-Bicycle wheel spokes
-k'nex components (specified later)
-A pillar drill (or handheld drill if not available)
-Assorted drill bits
-A band saw (or Tennon saw)
-Scroll saw (or Jigsaw / Coping saw)
-Hot glue gun
-Hot air gun
-File / rasp
A wood lathe
Step 1: Transmission Part 1
Firstly, disassemble your drill using a screwdriver. Discard the drill casing, battery and all electrical components apart from the motor.
Next identify the planetary gearbox. It is usually behind the chuck contained within a nylon casing. Depending on your drill, there may also be a clutch mechanism which needs to be removed.
To access the gearbox, first remove the chuck. It is often secured by a reverse-threaded bolt which can be accessed by opening the chuck all the way. Once this is unscrewed, the chuck should simply unscrew in the normal direction. Keep all of the chuck components as they will be needed again later.
Once the gearbox has been removed, open up the casing being careful not to lose any components.
Step 2: Transmission Part 2
Once the gearbox has been opened, remove the top row of planetary gears and any clutch components that the gearbox may have as indicated in the diagram.
It is necessary to remove these gears as otherwise the gear ratio will be too high for the turbine to turn. For use in a wind tunnel, the ideal gear ratio is 1:5 to 1:6. For use outdoors, we recommend around 1:3. It may be necessary to choose your drill based on this.
Step 3: Transmission Part 3
In this step, the gearbox is modified to better suit the requirements of the turbine.
If your gearbox features a clutch, the gearbox will have an outer nylon casing and a steel cylindrical gear (with teeth on the inside) sitting within this. With the clutch gone, it is free to rotate. This is undesirable as it will not allow the gears to work.
To prevent this, the cylindrical gear must be secured to the outer casing. this can be achieved by jamming steel shim or thin sheet metal into the gap between the two. If this does not prevent rotation, an epoxy resin can be used.
If your gearbox does not have a clutch, this part is not necessary.
It is likely that your gearbox has a steel o-ring that rests between the gearbox lid and the top row of gears. Now that we have removed these, the o-ring needs to rest against the bottom set of gears.
To achieve this, the diameter of the o-ring needs to be reduced so that it can sit within the cylindrical gear.
If your gearbox does not feature an o-ring, it may be necessary to make one from scratch.
Create a circular spacer from MDF using the drill for the central hole and a scroll saw / coping saw for cutting the circle.
The spacer must fit inside the cylindrical gear and be the same height as the row of gears removed.
Ensure that any sawdust is removed from the spacer before it is placed inside the gearbox.
Step 4: Connecting the Transmission and Generator
In this step, the generator is joined to the transmission.
Unless you wish to use the motor that came with the drill for generating power, the shaft of the drill motor should be cut from the motor retaining the gear on the end of it. This can be done using a hacksaw. Try to leave 1 cm of shaft so that it can be easily fixed to the new generator (motor).
Once this is done, attach the gear and shaft to the new generator using the brass shaft coupling. It may be required to drill out the coupling to the correct diameter in order to do this. Be ready to disassemble this arrangement later to adjust the length.
Make a keyhole-shaped mounting from MDF using a scroll saw. There should be a hole drilled in the middle of this. Most DC motors have a cylindrical protrusion at the front containing the bearing for the shaft. The hole should be drilled to this diameter so that the motor can be located centrally in the mounting.
Most motors also have two threaded holes in the front surface. In the mounting, drill two blind holes where these are located when the motor is fitted. They should be larger in diameter than the threaded holes in the motor casing. Once this is done, countersink the holes from the opposite side of the mounting (The gearbox side).
Drill two further pilot holes in the mounting in such a way that the gearbox lid can be fixed to the mounting using self-tapping screws. Ensure that the gearbox lid is perfectly central to the mounting.
Find countersunk bolts that fit the threaded holes in the motor casing and bolt the casing to the mounting from the gearbox side. Next, screw the gearbox lid to the mounting also from the gearbox side.
Finally, reassemble the gearbox with the mounting and motor attached. Ensure that the gear attached to the motor meshes with the other gears. Adjust the shaft length if necessary.
Step 5: Constructing the Blades and Boss
To construct the boss, cut a length of dowel on the band saw around 40mm long. Drill a hole down the centre of the dowel using a centre finder to determine the centre. The hole should be 7mm in diameter.
For greater accuracy, this can be done with a wood lathe.
Next, seven equally spaced diagonal slots must be cut into the dowel (one for each blade). Each slot should be at an angle of 35 degrees relative to the central axis. To achieve this, mark out 7 equal segments on each circular face and offset them so that when a line is drawn between two similar points, the correct angle is achieved. Cut the slots with a junior hacksaw ensuring that they are all the same depth.
To create the blades, first create a paper template in the required blade shape then use this to cut 7 blades from the 1mm thick polystyrene sheet using scissors.
To achieve the same twist in each blade, a former must be created. To do this,glue 4 pieces of MDF together using PVA to form an 80mm high block. When the glue has set, file down one corner to achieve a smooth curve.
Form each blade over the former using a hot air gun being careful not to over-heat the blade. Then, slot each blade into its slot and secure with hot glue.
Cut 7 bicycle spokes to the length of the blades using a hacksaw.
Drill a small diameter pilot hole into the dowel just behind each blade. Screw the bicycle spokes into these. They should self-tap. Having done this, secure each blade to its bike spoke with a dab of hot glue at the blade tip.
Step 6: Assembly
Firstly, reattach the chuck to the gearbox.
After doing this, take the white, round K'nex component and align it centrally with the back of the boss. It may help to place the yellow rod piece in the hole at the centre of the boss first and slot the white piece over it to find the centre.
Once you are certain it is central, drill two pilot holes diametrically opposite each other through the holes in the white component and secure it to the boss using self-tapping screws.
Following this, construct the arrangement of K'nex shown in the image but with the turbine blades and boss screwed to the back of white component. Take the long end of the yellow rod, place it in the re-attached chuck and secure it in place.
Finally, construct a stand for the turbine from MDF and dowel. The example shown is to be used in a wind tunnel and so the stand is very short. It is suggested that for outdoor use, a taller stand is used.
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