The structural hub of the front corner. Carries the wheel bearings and reacts every tire load into the arms, the tie rod and the actuation rod.
Connects the spindle bearing housing, the lower ball joint, the tie rod mount, the top mount connection, the brake caliper mounting holes, the wheel speed sensor mount and the rotor temperature sensor mount into one machined part. The upper ball joint is housed in a separate top mount rather than in the upright, which keeps the upright machining simpler.
Design starts by defining the geometry points (lower ball joint, upper ball joint, tie rod connection, spindle bearing location, brake caliper mounting) and then connecting them, sizing each hole and tab. Increased bearing size on CR26I led to a larger housing, and the geometry change from CR22 led to a new architecture. Material selected on yield, density, cost and stock availability: 7075-T6 at 73 ksi yield, 83 ksi tensile, 0.108 lb/in^3 and $230 for two uprights, against 6061-T6 (40 ksi, 45 ksi, 0.108, $200) and 4340 normalized (103 ksi, 161 ksi, 0.289, $1076). A reduced cost of 7075 relative to 6061 that year, from market conditions and a new vendor, made 7075 the clear choice. From the design reports and one-pagers: Design considerations from the CR22 Wheel Hub System Design Report: 1. Connecting geometry points. Use double-shear tabs with bolt holes in mind. The space between tabs depends on the ball bearing thickness plus spacers; tab thickness comes from standard tab thicknesses. 2. Maximum allowable deflection. Difficult to quantify or validate, but setting an allowable target makes the iterative design go smoothly. Deflection shows up as camber and toe change under load. The only real qualitative check is a driver feeling the difference between a low-deflection and a high-deflection model, which is not affordable. 3. Sensor location and type. The brake temperature sensor mounts to the upright to monitor rotor temperature, with the brake subsystem specifying mounting and distance. The wheel speed sensor mounts to the upright to read the wheel speed holes in the brake rotor. 4. Fitment to bearings. Typically a press fit to the upright, but not so tight that it restricts smooth bearing motion: between 0.001 and 0.003 in interference on the diameter between upright and spindle. Modelling starts from the geometry points the geometry designer supplies, plotted as a fixed 3D sketch and labelled. Model the top mount early so the upper A-arm angle comes out right, and keep the double shear tab centres on those reference points.
Wheel load applied as a remote load from the contact patch to the bearing faces. Lower ball joint and tie rod mount bolt faces resist lateral and longitudinal motion; the upper ball joint resists all translation; for braking a moment reaction is applied to the brake caliper bolt faces. Global element size 0.045 in, second order wedge elements. Cornering: maximum von Mises 26.7 ksi, yield FoS 1.5 in 6061-T6 or 2.7 in 7075-T6, with peak stress close to the remote load nodes. Braking: 23.2 ksi, FoS 1.7 in 6061-T6 or 3.1 in 7075-T6. From the design reports and one-pagers: CR22 approach: fixtures at the ball joints and tie rods, loads applied to the bearing surfaces and the brake caliper mount. Remote loads are used for the bearing loads to mimic the induced bending moment. Any braking force must be applied at the centre of the wheel so the moment is not double counted alongside the braking torque applied to the caliper mount. Elastic boundary conditions help relieve stress concentrations, with stiffness set arbitrarily higher than a solid steel support structure would give.
CAM in Autodesk Fusion 360, machined on the HAAS TM2P mill. From the design reports and one-pagers: Manufacturing limits that shape the design: no space or fillet may be too small for the ball nose end mills, with 0.125 in radius as the working minimum and 0.0625 in doable but not optimal because 1/8 in ball noses are very sensitive. Tools must be long enough to reach every surface; a 3 in deep blind pocket may have no tool that can clear it. Workholding must be designed alongside the part for multi-setup work, keeping the part rigid and minimising vibration while the vise holds the workholding. Outsourcing is permitted with proper planning, but hands timeline and quality control to the outsourcer, so they should be contacted as early as possible, especially if the work is free and therefore not billable to them.
Al 7075-T6. From the design reports and one-pagers: Material selection reasoning from the report: steel alloys are cheap and strong but three or more times denser than the alternatives. Aluminium is the standard choice, with 6061 and 7075 both viable and 7075 stronger but more expensive. Titanium would be the best material on strength and weight but is described as impossibly expensive for a student team to buy in good conscience. CR26I selected 7075-T6 partly because market conditions and a new vendor made it cheaper relative to 6061 that year. From the cost report drawings and CAD: From the cost report drawings: Al-6061T6 (CR25_Upright_FL_FINAL_LargerLowerBJ).
Single-body analysis shows singularities close to boundary conditions and models no bolt preload, which limits how far the part can be weight-optimised with confidence. The full-corner model built for CR26I showed that joint preload alters stress distribution and that resultant stresses in the full corner model are lower than in single-body simulations.
Dimensions called out on the cost report drawings. These are the figures printed on the drawing, not a labelled specification; open the drawing itself for what each one refers to. CR22_SUS_FL_Upright_RevFinal (in): 3.175, 2 x 0.483, 0.013, 1.00, 0.800, 2.22, 5.15, 4.128, 5.500 CR22_SUS_F_Upright_RevFinal (in): 3.175, 2 x 0.483, 0.013, 1.00, 0.800, 2.22, 5.15, 4.128, 5.500 CR25_Upright_FL_FINAL_LargerLowerBJ (as drawn): 55.56, 5.56, 175.34, 17.53, 58.80, 5.88, 62.00, 6.20, 43.18, 4.32 CR26I_FrontUpright (mm): 150.78, 15.08, 55.56, 5.56, 4.32, 43.18, 5.88, 58.80, 8.40, 175.34 Source: Cost report drawings: CR22/Document Submissions/Cost Report/Suspension/Cost Report Drawings/Suspension & Shocks/Front Upright Assembly/CR22_SUS_FL_Upright_RevFinal.pdf; CR22/Suspension/Design/01_Cost_Report/Cost Report Drawings/Suspension & Shocks/Front Upright Assembly/CR22_SUS_F_Upright_RevFinal.pdf; CR25/Suspension/Management-Comp/Cost Report/Drawings/Sus Shocks - Front Upright Assembly/CR25_Upright_FL_FINAL_LargerLowerBJ.pdf; CR26i/Suspension/Competition/Cost Report Drawings/Suspension and Shocks/Front Upright Assembly/CR26I_FrontUpright.pdf Quantity per car, as costed: 2
Nothing in CrimsonStorage covers these yet.