ENGS 89/90 Reports

Project Advisor

Ron Lasky


Solomon Diamond Doug Van Citters

Document Type


Publication Date

Winter 3-6-2020


Recently the micro mobility market has exploded as an affordable and practical transportation solution for many people. A majority of these people live in urban centers where a compact low speed transportation vehicle is sufficient. For our sponsor’s product to reach this market it needs significant refinement in its drivetrain. This transmission redesign makes significant strides towards making a market ready product. This project is based around improvement upon our sponsor’s previous iteration of a propane powered motorized bicycle. Our sponsor’s vision for this product is to develop it to become a competitor in the micro mobility market. The previous design has notable shortcomings in safety, rideability, and performance. To address these shortcomings the transmission was redesigned. The safety issues with the previous design stem from rider proximity to uncovered drive components. The previous design had a large sprocket rotating at high speeds inches from the rider. This sprocket, in addition to a series of chains connecting different drive components near the rider seriously compromised rider safety. The new design houses high speed rotating components in enclosed gearboxes and reduces the length, speed, and number of chains near the rider. Any drive components not housed in a gearbox, and within the pedal radius of the rider will be covered by a chain guard in compliance with Dartmouth Formula Hybrid standards. With these new improvements the prototype will be much safer to ride. Moreover, the new design adds an automatic, 3-speed shifting mechanism that is controlled by on-board electronics and an internally-geared rear hub. This places the bike in compliance with state laws that require automatic shifting if the bike can change gears. Along with safety upgrades, this new transmission design significantly impacts rider comfort and vehicle performance. The previous design had a pedal width of 10in, much wider than industry standards. By reorienting the engine we reduced the pedal width by 3.5in bringing it in line with other bicycles. The variable speed drive will provide increased performance by allowing the engine to run at a more reasonable rpm and more effectively transmit power to the wheel. By detecting wheel rpm, the electronic system can gear the power train up or down accordingly. With this project we have constructed a transmission design, which, with slight modification of the bicycle frame, will offer significant improvement over the previous design. We have constructed a robust test bench which has allowed us to collect good data on how this transmission would perform on the road. We compared the data with information we have on the previous design to develop a full picture on the improvement offered by our transmission design. Without a competing design, electric bikes and their manufacturers will be left unchallenged by alternative energy solutions. This will mean the same high prices for their technology and less innovation in this field in general. In completing this project, we have brought a potential competitor product closer to entering the market.

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