Using SOLIDWORKS Solutions to Build a Hand Crank Flashlight: Part 1 – Mechanical Design

Article by Joseph Lyon, last updated on January 5, 2018

While working as an engineering intern in the electrical department at Javelin, I am putting my academic knowledge to the test by creating a fully functional hand crank flashlight. This will be an excellent addition to any emergency/zombie apocalypse survival kit. To add to the challenge, I am using salvaged electronic components and 3D printed hardware when applicable. I will document my “enlightenment” through a series of blog articles.

A 1990’s Compaq computer motherboard laying around my house will be the source of most of my components

A 1990’s Compaq computer motherboard laying around my house will be the source of most of my components

Project Scope: “Shedding Some Light on the Situation”

The goal of the SOLIDWORKS Flashlight Project is to engineer a hand crank flashlight that will stay lit longer and weigh less than traditional models. As the flashlight will be created almost entirely with in house parts, the project is environmentally friendly! Components from salvaged electronic devices of mine and 3D printed hardware will be used. Additional materials will be purchased only when necessary. I will also be using SOLIDWORKS and SOLIDWORKS PCB together to streamline my electromechanical design process.

Background: The Science of Power Generation

A hand crank flashlight works by converting rotational mechanical input into electrical energy. As the crank is rotated, a shaft connected to a generator spins, thereby producing an electrical current throughout the circuit. The electricity is regulated to maintain a steady voltage and power an LED. Although the concept of a hand crank flashlight is not new, power generation and storage continue to be popular subjects in the field of engineering.

SOLIDWORKS Flashlight Project Design Process

My first step in the design process began with a rough 15-minute part drawing in SOLIDWORKS CAD. Engineer or not, it was apparent changes needed to be made.

SOLIDWORKS Flashlight Project Model

1st Design Iteration

Lightweight Design: SOLIDWORKS CAD

To meet my criteria of being more lightweight than traditional store-bought hand crank flashlights, I made several modifications to my design. Some of these changes included: utilising the “shell” feature to create a hollow body, reducing the size and shape of the LED housing, adding grip, modifying some dimensions to streamline the design and creating a latch to easily insert a circuit board.

SOLIDWORKS Flashlight Project Drawing

2nd and Current Design Iteration

I will be using 3D printed ABS plastic to outfit the flashlight instead of traditional aluminium and rubber. To obtain an accurate estimate of the weight of the design, I utilized the built in “Mass Properties” feature of SOLIDWORKS.

The mass properties of the hand crank flashlight taken in SolidWorks CAD

Hand crank flashlight mass properties

A mass of 84.23 grams was measured without any electronic components, which is incredibly light! No pun intended. The average mass of traditional store-bought hand crank flashlights is approximately 300 grams. However, this value also accounts for the added mass of electronic components.

Supercapacitor and Joule Thief Circuit: “A Light that Lasts”

Tired of having to rely on rechargeable batteries that lose their ability to retain energy over time? Well, me too! My solution to this problem is to apply the emerging power storage technologies of a supercapacitor, in addition to a joule thief circuit. A supercapacitor stores energy on the surface of its material and does not degrade over time. A joule thief circuit operates by boosting low voltages in a weak DC power source to higher usable voltages, by means of rapid voltage oscillation. Coupling these two technologies together ensures that the most amount of power can be harnessed from crank rotation. Take that, Energizer bunny!

The electronic components making up a supercapacitor and joule thief circuit

The electronic components making up a supercapacitor and joule thief circuit

Future Plans: “The Light at the End of the Tunnel”

My timeline is to complete this project in approximately 2 months. However, as every engineer knows, the first unwritten rule of design is “nothing ever gets built on time or within budget”, so we’ll have to wait and see. I am continuing the mechanical design iteration process, devising a comprehensive circuit schematic, and taking electrical performance measurements along the way. In addition, I am documenting my first-time experience using a Stratasys 3D printer and will provide a comprehensive bill of materials for future designers.

Keep an eye out for my second installment my SOLIDWORKS Flashlight Project, where I will be implementing my schematic design using SOLIDWORKS PCB.

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