Livable Last-Mile Delivery Vehicle
Recently, the CLA team finished designing and started manufacturing a first-generation delivery trailer, the CMW Mule. Featuring a 3-wheel design, the trailer is built with cost and maintenance in mind and can carry more than 500 pounds and up to 54 cubic feet of cargo. These trailers increase the maximum carrying volume and weight of a traditional bicycle without significantly decreasing the benefits of a bicycle’s maneuverability and smaller profile. However, compared to the large trucks currently in use, these trailers leave the cargo more exposed to the weather during transportation and are not equipped to properly secure the cargo in place. Therefore, one of the purposes of this project was to design a modular cart that wheels on and off the back of the CLA prototype trailer that protects and secures cargo on the vehicle during transport and facilitates faster delivery times. Additionally, the director of CLA expressed interest in using an electric assist hub-motor in the front wheel of the tricycle trailer and incorporating regenerative braking.
Because the trailer bed was 8” off of the ground, ramps needed to be made to load the cart onto the trailer. The size of the wheels and the slope of the ramp were determined by common ramp standards in construction work areas and commercial moving trucks and also by the geometry of the trailer to prevent the cart from scraping against the edge of the trailer during loading.
The material choice of different components of the cart was decided based on reducing the manufacturing cost, weight, and ensuring the sustainability of the overall product. The base of the frame was constructed with wood. The folding skeleton was supported with aluminum L-beams. The folding panels were sewn together layers of recycled PVC vinyl and corrugated plastic.
The folding skeleton detaches from the wooden frame with friction fit slots in the aluminum that interfaced with hardware installed in the wood. Once all four corners of the aluminum slot into place, the hardware can be easily adjusted to prevent accidental disassembly. The aluminum pieces also slot together with 3D printed corner joints. However, the entire assembly can only be disassembled into 3 pieces, held together by flexible joints by the PVC vinyl.
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The second component of the mechanical engineering focus of the project involved working in adding an electric motor to the front wheel of the trailer and programming a regenerative braking control algorithm and electric hardware. Regenerative braking is a somewhat novel and undocumented technology for use in bicycle trailers; the benefits and drawbacks are still not fully understood in the cycling logistics industry. However, at the beginning of the Spring semester, the low-voltage voltage regulator in the motor controller broke and could not be fixed by the manufacturer before the project deadline.
Working alongside the civil engineers, a logistics warehouse layout was developed to facilitate efficient vehicle flow in and out of the building. Once the layout was developed, the civil engineers developed a 3D model of the warehouse and ran analysis of the building structure for the proposed site in Red Hook, Brooklyn.
For the mechanical engineering senior design project, I worked in an interdisciplinary group of mechanical and civil engineers who were all interested in tackling transportation-related design issues in New York City. The group narrowed in on improving sustainable delivery vehicles and designing urban architecture and infrastructure that could accommodate widespread and large-scale use of these newer and better vehicles.
The group discussed the vehicle and building design with community board members who knew and represented the interests of the local community surrounding the rise of logistics buildings in the area, and traffic engineers who gave feedback and insights on what to consider for the vehicle design, operating procedure, and how it could effectively integrate with the building layout. We also consulted with experts in the urban logistics industry, Upcycles Transit Inc. founder Nick Wong and Cycling Logistics Association (CLA) founder Dan Ilkay. In fact, the group collaborated with CLA and used their recently designed trailer frame as the foundation of the vehicle design.
The final design of the cart rolls onto the trailer with 2 ramps and large 6” diameter caster wheels. The cart has single side access that allows loading both on and off the trailer. When not in use, the cart can be easily disassembled and folded from 48” tall to 10” tall. Various locking mechanisms were designed and manufactured to ensure rider and pedestrian safety.
To prevent the cart from rolling or tipping off the trailer while in motion, a pin-lock mechanism was designed and manufactured to lock the cart on both side to the chassis of the trailer. Springs ensure that the failsafe position locks the cart in place. Additional failsafes on the trailer bed that prevent the cart wheels from moving were installed. A cable was also added to the cart that the user can wrap around the trailer chassis to ensure the cart does not roll off.
Nevertheless, a dynamic model was developed to estimate the energy reclamation of regenerative braking in various real-world scenarios based on the aerodynamics of the vehicle, road grade, measured motor power curves and battery charging documentation.
In addition, the performance of the mechanical braking system currently installed on the trailer was evaluated with a minimum braking distance test. The mechanical braking system employs an overrun brake in the linkage between the towing bicycle and the trailer, and uses a disc brake on the front trailer wheel. The braking test involved getting the trailer up to various speeds and loading it with various cargo weights and measuring the distance the vehicle travels before coming to a full stop when the disc brakes are fully engaged. The purpose of this test was to compare the braking distance of a fully loaded trailer to a common bicycle to gauge what maximum travel speed and loading weight the vehicle should be limited to. The data would also be useful to compare to the braking distance of a regenerative braking system to evaluate the safety of regenerative braking.
The project was presented at the senior design poster presentation showcase and the Cooper Union end of the year show. The group also won the best senior project community engagement award for collaborating with different local industry experts and members of the community in Red Hook.