To design and manufacture the load-bearing structures that safely support the high voltage battery and its surrounding components, and to mount them to the frame.
A welded 6061 aluminium accumulator container built on a tower layout: the battery segments form the base, with separate upper and forward compartments for the HV and LV components. Floor 0.16 in, external and internal walls 0.125 in, lid 0.125 in. A structural lid encloses the top, stiffens the external walls, isolates the interior and keeps water out for the rain test, sealed with an internal rubber gasket and fastened with 5/16 bolts through aluminium blocks that hold the locknuts. A non-structural polycarbonate segment lid isolates the battery section from the rest of the container. Two structural cross bars per section, fastened with 5/16 bolts and rubber-faced against the cells, provide vertical retention to 20 g. Ten welded aluminium mounts attach the container to the frame. Each segment side wall carries a perforated section, no more than 25% of that section's area, sized by the fan speed and airflow the cells need.
Container designed around battery layout, designed for serviceability first, then tuned for stiffness and lightness, with ease of manufacturing kept in mind throughout. Load-based mounting over corner-based mounting. Corner-based requires an attachment at each corner of the rectangular structure, which lands at 10 points anyway but leaves them where the geometry puts them, making service difficult and the design inflexible. Load-based requires a point count derived from accumulator weight, also 10, but lets those points go where they are serviceable and lets them move for packaging. Weld the mounts rather than bolt them. Welding keeps the container serviceable and increases tear-out area. It also drove the material choice: the design moved from steel to 7075 aluminium and finally to 6061 once welding was settled. 1. Take the battery segment geometry from Energy Storage: five segments at 15 lb each. 2. Lay out the tower, then set wall thicknesses from available stock above the rules minimum (floor 3.2 mm, walls 2.3 mm). 3. Validate segment structure by hand using Roark's formulas for a plate under uniform pressure, at 40 g fore/aft and lateral and 20 g vertical. Fore/aft gave sigma_max 5.75 ksi and FoS 2.78; lateral gave 9.17 ksi and FoS 1.75; down gave 0.833 ksi and FoS 19.2. 4. Validate each mount independently for static shear, pull-out and bending, fixed at a 0.25 in weld perimeter, at the 15 kN rules requirement. 5. Run structural equivalency for the load-bearing columns: mounting tabs, side wall and front wall cross sections, with I = A*t^2/12. 6. Waterjet the walls, weld on a jigging table with aluminium cube jigs, mill the mounts and weld them to the side walls.
- Package to balance serviceability against structural requirements. - Balance stiffness against weight. Container 31.23 lb bare, 1.8 lb of mounts, 33.07 lb assembled. - Ensure the quality of the structural simulations. - Ensure rules legality. - Ensure manufacturing quality.
- Warping when welding an aluminium container. Countermeasures adopted: strong heat sinks and fixtures, tight fit-up and tacking, clamping and tacking all corners before committing to a full weld, and a stitch or skip weld pattern to distribute heat. - Perforation area interacts with structure. Once the perforated area is fixed by cooling requirements, every area-derived quantity including moment of inertia has to be recalculated. - Mount design sensitivity to fillets. Across iterations, larger corner fillets and thicker flanges lowered peak stress; the mount got thicker as the material moved from steel to 6061.
Roark's Formulas for Stress and Strain for plate hand calculations. FEA for the container under collision load and for independent mount validation in shear, pull-out and bending. SolidWorks for the container and mount geometry. The Structural Equivalency Spreadsheet for rules compliance.