Checkpoint 1:

1st Draft CAD Models (04/06/2018)

Electrical Assembly/Testing

To test the feasibility of charging a cell phone or other small personal USB devices using the portable turbine, the electrical components were soldiered and assembled. The generator and step-down buck converted were connected using simple bullet-type connectors, and an in-line USB voltmeter and ammeter was connected in-line to monitor the exact output.

To simulate the turbine spinning in wind, a drill motor was attached to the generator shaft and run at approximately 1,800 RPM. At this speed, the buck converter was able to convert the higher voltage generator supply to a USB-acceptable 5.12 volts. Per spec calculations, the output at this speed is around ~0.15 amps, which is under the required amperage to charge an iPhone. While higher RPM values are expected using the actual turbine blades which in turn will produce much higher amperage, 0.15 amps is still sufficient for charging other small devices such as a USB portable battery, which many users may find is a more convenient charging solution.

Housing Design V1.0

Housing base including motor seat, buck converter mount, and cutouts for generator shaft and USB port.

Generator mounting bracket with screws to ensure a secure clamp and prevent slipping.

Installed motor bracket includes tight tolerances (~0.5mm) on each edge to ensure proper alignment to minimized drag/wear.

Contoured lid with aerodynamic shape and tapered lip to ensure a secure fit (<0.1mm tolerance) and protect against the elements.

The assembled generator housing includes high-tolerance fits and a tapered-to-rear design to reduce overall dry and minimize eddy flows at the rear. The lid roof also includes an efficient handle to allow for easy access during the design and testing phases.

Turbine Blade Design V1.0

The design of the wind turbine blades were largely based on a previous study conducted in ME107, a mechanical engineering experimental laboratory class at UC Berkeley. The study determined that in the case of a wind turbine of this scale, a NACA 0012 airfoil blade profile at a 14° twist and 50% taper was the most efficient in terms of power generated.

In order to keep in line with the "portable generator" philosophy, the turbine blades are designed to be detachable from the central hub for ease of transportation, especially useful in situations where storage volume is limited. The blades slide into designed notches within the central hub through a tight transition fit. The central hub is attached onto the generator axle through a similar fixed transition fit.

The tolerance of the components are expected to be in the +/- 0.5mm range, but must account for the potentially rough surfaces of the 3D printed products. Post-printing processing will most likely be required in order to obtain the desired smooth profile on the appropriate joining surfaces.

Possible future design changes to the turbine design include:

Lengthening of the blade base and inclusion of chamfers and fillets to decrease the possibility of a stress concentration.
Improving the aerodynamic profile of the central hub
Upgraded locking mechanism to ensure blades will not disengage during operation

Tri-blade central hub with notches into which blades are installed into. A tight transitional fit allows the blades to be secured by with hub through friction while being easy to uninstall.

The individual blade features a NACA 0012 airfoil blade profile at a 14° twist and 50% taper for maximum power generation efficiency. Post-processing for the 3-D printing manufacturing method may include sanding the blade surface to prevent energy loss to the surrounding air while in operation. In addition, due to the tight transition fit between the components, sanding may be required on certain profiles due to the inherent roughness of 3D printed components.

Tri-bladed turbine design. Individual blades are designed to be detachable for ease of transportation and reduction of storage volume. 3D printing with an appropriate polymer allows for the manufacturing of a turbine that is lightweight, cost efficient while maintaining rigidity and strength during operation.

Mounting Concepts

(Tree clamp, cables, ground stand, kite mount, etc)

The initial kite sketch is basically an idea of the future energy technique. By combining the kite and turbine as well as the electricity device, we could realize an energy saving approach - charging phones when having fun fly the kites! Furthermore, if the plan could be mature enough, we may apply that into industry field to take place of the huge windmills.

Focusing on the handmade kites, the materials can be quite accessible. for example, the use plastic bag may be used as the kite cloth and plastic stick as kite frames. As long as it is light but stiff, there would be possibility for the kite to fly in the sky.

However, there are still some obstacles before flying the kite:

The material of the wire considering its electricity-conductivity and weight;
The location of the assembly and housing device;
The possible low efficiency of the turbines on the kite.

We need more model experiments to practice this eco-friendly kite.

Notes from 04/06/2018 discussion meeting with GSI:

Have back end comparison with current market alternatives (specifically folding/flexible solar chargers)
- Wind turbine will provide significantly more power (faster charging), works day and night, works without sunlight (in a storm)
- Solar is lighter, sunlight is usually more reliable than strong wind
Have Ashby/material index breakdown for why we chose plastic for blades vs other materials
IMPORTANT: Have clear definition of who our target audience is, and explain how we are catering to their needs
- Weight considerations, size considerations, weather considerations, cost considerations
- We may needs to reduce radius of turbine and add more blades (GSI thinks radius may be too large)

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