Electric Scooter Charging Station
Summary:
The purpose of this freshman design project was to design a modular and low cost electric scooter charging station for the Rice Transportation Department. Our team of three worked through the engineering design process to define the problem, brainstorm solutions, prototype solutions, determine a final design, and evaluate our design.
Our final design consists of a PVC tube structure with an outdoor-rated 120V outlet and rain protection roof (the PVC tubes resemble steel tubes). The structure provides space for up to four scooters to attach and the tubes are filled with sand to prevent the structure from falling over in the wind. The rain protection roof connects to the structure via hinges and can rest either in the upright position or flat on the structure supports. Handles make it easier to move.
The design is completely modular. To connect another unit, remove the plugs on one side of the structure and connect another unit.
As the leader in our group, I guided our team through the decisions in the engineering design process.
The Problem:
Biking has been the main mode of transportation on Rice’s campus, so the need for scooter parking was minimal. In the past couple of years, scooter usage has exploded on campus.
This has resulted in bike rack competition, obstructive clutter from scooters left out in the open, and many unsecured scooters. Additionally, many scooter owners choose not to use their scooters due to range anxiety caused by a lack of available charging spots on campus. In order to address the rise in electric scooter usage, our goal is to make an eco-friendly and modular scooter parking and charging station (SPCS) that finally introduces safe and sustainable scooter parking into Rice’s campus.
Our goal is to build an eco-friendly Scooter Parking and Charging Station that encourages scooter usage and limits bike-rack competition.
The problem: electric scooters being left outdoors are unsecured, without a place to recharge, and block walkways. Scooters shown are outside South Cafeteria in September 2021.
Design Criteria:
Table 1 details our design criteria constraints and objectives. We want our station to last for at least three years to keep down costs and increase practicality for our design as a solution on campus. We wanted to include one lock per scooter section so that users so scooters are secure. From our research of common scooter sizes, we chose to accomodate a scooter size of at least 30x30x5 inches. We wanted each SPCS to connect to at least two others so that it can be practically expandable. Our client requested a cost of at most $500 for a SPCS. We wanted our charging station to be able to charge at least 80% of scooters on campus so that the stations would be frequently used. Lastly, we wanted Rice students to enjoy the sight of the station so that our solution can be accepted on campus (see Table 2).
Table 3: Pairwise Comparison Chart showing the importance ranking of design criteria. Most to least important:
Lockable, Sizeable, Versatile Charging, Modularity, Weather Resistance, Low Cost, Aesthetically Pleasing
Idea Brainstorming:
Our SPCS problem breaks down into the following categories: Locking, Modularity, Charging, Weather Resistance, and Arrangement. We broke down the SPCS problem this way since each of these categories has distinct solutions and these solutions can be interchanged to form different complete solutions.
Our brainstorming process involved two 25 minute sessions of alternating brainstorming and idea sharing periods. In the first brainstorming session, we used the Writing Slip Method, where we wrote our own ideas down on cards. In the second brainstorming session, we used the Card Method and used existing ideas to create new ideas. We found that the best ideas came from brainstorming ideas on our own.
The result of our brainstorming process is 54 ideas, which were all incomplete solutions that applied to a specific design block (shown in the images on top). Some of the inspiration for our ideas came from our research of existing solutions. For example, a couple of our locking mechanism ideas came from finding existing public scooter parking stations.
Design Selection:
We used a morph chart to form 15 complete solutions from our 54 incomplete solutions. Using two Pugh screening matrices, we rated each complete idea against our design criteria and ranked the ideas. Next, we selected seven of the 15 solutions that ranked highest to be evaluated in the Pugh scoring matrix. The total score for each solution was calculated by weighting the criteria. From the scoring matrix, we chose the Scooter Docking Station over the Curved Rack because the Curved Rack solution was too similar to the current bike racks on campus.
Conceptual Idea Sketches
Our first design consisted of a shed-shaped main structure with the base and back walls made of wood. The roof is made of thin metal. We cut out a window in the back wall to make the design more aesthetically pleasing. We were considering adding metal poles on the base corners to help hold up the roof.
On the back wall, pairs of U-bolts provide secure locations for users to lock their scooters. Outlets between U-bolts allow scooters to be plugged in for charging. Divots ensure that locked scooters do not move around easily.
Low Fidelity Prototype:
Our low fidelity prototype was a 0.15 scale model replica of our design. We primarily used cardboard precisely cut to the measurements of our design. We used hot glue to connect the base, back wall, and roof together. Next, we realized that we needed a stronger connection to hold up the back wall and came up with the idea of using a triangle to support it. Additionally, we decided to use poles made of metal (straws in this prototype) to hold up the roof. Lastly, in this prototype we extended the roof length on the sides to better protect the electronics and scooters against rain. We calculated how far the roof needs to extend on the sides to keep the base dry from rain at a 20 degree angle. This way, our scooters and scooter chargers can stay dry from light rain.
2nd Low Fidelity Prototype:
After our first prototype evaluation, we realized our design was infeasible to construct due to its immense size and material usage. We worked hard to scale down our design while still keeping the same charging, locking, and rain shelter elements. We decreased the height from 7 feet to 4.5 feet and changed the structure from a shed to one made of tubes where the roof can rotate on hinges. We thought that tubes would be lower cost and easier to build. Our new design still provides rain protection with the roof but it can be moved to allow people to lift it and access charging.
Medium Fidelity Prototype:
The purpose of this prototype was to build same design out of higher fidelity materials and to prototype the hinge mechanism. The roof has a support that comes out at a 45 degree angle as well as a slant in the roof material that ensures it doesn't rotate past a certain point.
Final Prototype:
Our final prototype is a 56 inch tall structure that is 58 inches wide and has a depth of 36 inches. The main structure is made out of PVC pipes (in place of metal tubes). We designed a ski-like arrangement for the bottom supports to ensure the stability of the structure whenever the roof is in its closed or open position. There are also two support PVC pipes that protrude diagonally from the structure to hold up the roof. An outlet hub is incorporated into the middle of the center pipe, or our locking bar, to ensure users’ equal access to charging outlets. The roof is made out of fluted polypropylene and is connected to the top PVC pipe through our hinge design. We designed a piece of laser-cut wood that serves as a harder material that can support the metal hinge and bolts that go through the flexible roof.
Testing:
Our team conducted seven tests, one for each design criterion. All of these tests were fairly basic, such as making sure our station was large enough to fit a certain number of scooters. We found that it was difficult to evaluate modularity since the definition of this design criteria was a bit vague. We passed most tests except for aesthetically pleasing. It was difficult to prioritize aesthetics when we were just trying to finish a working proof of concept.
Key Takeaways:
Working on Teams:
I learned the importance of communicating with my teammates and setting clear expectations for our work. I also got practice splitting up the work we needed to do into pieces that each team member could accomplish in the same period of time. Lastly, I learned the importance of planning ahead. Our team did not plan ahead very well in the last couple of weeks and made many decisions "on the spot”.
Engineering Design:
I learned how to apply engineering design process and why it works. I got experience with client interviews, making design criteria, brainstorming solutions, evaluating solutions and choosing a solution, prototyping and iterating our design, and testing our design against our design criteria. While design criteria at first did not seem useful, it greatly helped set up the rest of our project for success and ensure our design would solve our problem. In the end, our design meets most (5/7) of our design criteria and is very close to meeting the last two.
Tools and Skills:
I learned how to use 3D printers to print 3D files and how to use laser cutters to cut out vector files. I also improved my CAD skills and re-learned how to use Adobe Illustrator. Aside from technical skills, I learned how to communicate design information effectively and concisely with our two team presentations on our design and prototyping. I also learned how to write technical memos that demonstrate our team's progress.