Locate the rear wheel relative to the chassis and carry the resulting loads back into the frame.
Same architecture as the front. Rear geometry was slightly altered on CR26I to minimise misalignment-induced bending. Design Philosophies and Processes: Inherited from the Arms subsystem design process: 1. Take the geometry points from kinematics and the wheel loads from the load cases: CR26I front outside cornering 648.691 lbf vertical and 786.094 lbf lateral, braking 585.523 lbf vertical and 763.26 lbf longitudinal, combined 768.095 / 785.550 / 444.124 lbf. 2. Resolve loads into each member with Altair HyperWorks MotionView. 3. Size the tubes in the calculator against buckling and yield. CR26I front upper 0.375 in OD / 0.305 in ID at minimum FoS 1.946; rear upper same tube at 2.581; front lower 0.625 / 0.527 at 2.49; rear lower 0.5 / 0.402 at 2.62. 4. Analyse the spherical bearing holder with two FEA setups so the boundary conditions are cross-checked: bearing fixed with loads at the pullrod bolt and arms, then arms and pushrod bolt fixed with a remote load at bearing centre. Validate the tab stress against a hand calculation for a hole centred in a wall (calculated 18.95 ksi against 22 ksi FEA). 5. Weld in the jigging assembly, then measure the finished arm.
CR26I rear upper tube 0.375 in OD / 0.305 in ID gives minimum FoS 2.581 with 0.1875 in tab thickness. Rear lower tube 0.5 / 0.402 gives minimum FoS 2.62. Rear outside wheel loads: cornering 674.593 lbf vertical and 817.483 lbf lateral, braking 285.001 lbf vertical and 466.635 lbf longitudinal, combined 653.214 / 824.848 / 382.613 lbf.
Welded in the A-arm jigging assemblies.
AISI 4130 steel tube with welded spherical bearing holders.
Fault Vault, CR26I, Manufacturing, Potential Failure. The upper arms' ball joints became loose within the housing and had vertical compliance, theory being excessive staking force. Fault Vault, CR26I, Manufacturing, Potential Failure. The rear right upper fore arm was not long enough on CR25 because its frame tab had been welded in the wrong place. The arm was redesigned for CR26I to account for that difference and was still too short, so a modified rod end had to be used. The recorded cause is that the tube was simply cut shorter than it should have been. Corrective action: double check calculated arm lengths after cutting, coping and every other manufacturing step, before welding.
Double check calculated arm lengths after cutting, coping and every other manufacturing step, before welding. Upper bearing holders are now machined complete on the mill with soft jaws instead of having actuation tabs welded on, which cut A-arm build time from over 100 hours on CR25 to about 50 hours on CR26I.
CR26I rear upper 0.26 lb against CR25's 0.54 lb, a 0.28 lb saving. Fore tube 0.875 x 0.981 in at 9.23 in, aft tube 0.875 x 0.981 in at 8.05 in. Lower fore 0.402 x 0.500 in at 12.23 in (FoS 2.17), lower aft 0.402 x 0.500 in at 12.75 in (FoS 2.16). From the cost report drawings and CAD: 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 RL (as drawn): 26.10, 1.90, 0.79, 1.59, 40.10 CR22 RU (as drawn): 30.07, 1.27, 0.64, 29.29 CR25_SUS_RLowerAArm (as drawn): 384.8338.48, 397.8839.79, 261.29, 26.13 CR25_UpperAArm_Assembly_Steel_FreshProj (as drawn): 301.79, 30.18, 273.4327.34, 303.4230.34 Source: Cost report drawings: CR22/Suspension/Design/01_Cost_Report/Cost Report Drawings/Suspension & Shocks/Rear A-Arms/CR22 RL.pdf; CR22/Suspension/Design/01_Cost_Report/Cost Report Drawings/Suspension & Shocks/Rear A-Arms/CR22 RU.pdf; CR25/Suspension/Management-Comp/Cost Report/Drawings/Sus Shocks - Rear A-Arms/CR25_SUS_RLowerAArm.pdf; CR25/Suspension/Management-Comp/Cost Report/Drawings/Sus Shocks - Rear A-Arms/CR25_UpperAArm_Assembly_Steel_FreshProj.pdf
Nothing in CrimsonStorage covers these yet.