Boston-Power Custom Battery Packs for the Purdue University evGrand Prix
10 custom designed battery packs were designed and manufactured to be used by electric racing go-karts in the Purdue University evGrand Prix. The pack design was focused on the endplates, which would have the greatest impact on airflow to the rest of the pack, while designing for safety and weight reduction. Kaiser Aluminum donated by Alcoa, INC. was cut to size for the baseplates while standard aluminum bar stock was used for the sidebars of the enclosures. Polycarbonate sheets were used in order to protect the batteries from any impact while maintaining pack visibility, in addition to ensuring driver safety. Polycarbonate brackets maintained firm packing and spacing between the rows of cells. The custom made bus bars streamlined pack wiring. These design components were bolted together using standard 1/4”-20 bolts for ease of assembly.
The Boston-Power cells were tested at varying discharge rates to determine the cooling required to maintain safe operating conditions: forced convection at a speed of greater than 8m/s (17.9 mph). The go-karts satisfy this condition by reaching speeds of up to 20.12m/s (45 mph) during the maximum rate of discharge. The endplates, for safety, were designed to be 0.5” thick 6061 Aluminum and were modeled in Autodesk Inventor. The endplates were manufactured by Carney-Echelbarger Machining in Kokomo, IN to expedite production. Slots were milled into the endplates and covered with rubber insulation to increase the factor of safety from the battery terminals to the metal of the enclosure.
The custom made bus bars were used to connect rows of the Boston-Power battery modules in series for a final configuration of 14 in series and 2 in parallel (14s2p). Measurements were taken between terminals on adjacent batteries in order to design the bus bars. Calculations to determine the thickness of the copper (1/16”) for the bus bars were based on the required current draw. 144 working bus bars were cut from a copper sheet using industrial cutters. The terminal bolt holes were then drilled into each bar using a HAAS CNC Mill.
A standard kick scooter was converted to an electric drive in order to demonstrate and experiment with some of the potentials of electric vehicle technologies. A custom drivetrain was configured using large scale RC model components. This configuration consisted of a lithium-polymer battery, a motor controller, and an outrunner brushless DC motor. The output to the motor was controlled by the variable resistance of a throttle potentiometer. The mounting and housing for the drive-train was centered over the rear wheel to facilitate the friction drive. The motor mount featured a spring system to hold the motor in 2 positions: forced against the rear wheel and fixed away from the wheel (for the instance of a dead battery, to maintain scooter functionality).
Picnic tables are typically 6 feet long, widely used in parks everywhere. An 8 foot picnic table was constructed by modifying this standard design. The height of the 8 foot table was built to remain consistent with the 6 foot tables, adjusting the other features of the table to meet that requirement. Trigonometric calculations were performed in order to determine the toolpaths to meet the height requirement with properly sized legs and cross-brace supports. These supports fix the position of the legs relative to the table top, stabilizing the table and preventing it from wobbling.