House the outboard spherical bearing of the front upper A-arm and carry the actuation rod tab.
The junction where both arm tubes, the spherical bearing and (at the front) the pullrod all meet. On CR26I it is machined complete rather than having the actuation rod tab welded on, which is what removed most of the A-arm build time.
No part-specific design process is documented. The Arms subsystem design process applies: 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.
Two FEA setups with different fixtures so the boundary conditions cross-check each other. Setup 1, bearing fixed with loads at the pullrod bolt and arms: peak stress 33.5 ksi, yield FoS 1.991, maximum displacement 0.00359 in. Setup 2, arms and pushrod bolt fixed with a remote load at bearing centre: peak stress 27.2 ksi, yield FoS 2.452, maximum displacement 0.00384 in. Separate tab studies: 0.25 in thick AISI 4130 gives 14.1 ksi and FoS 4.48 for the holder, 19.46 ksi and FoS 3.24 for the tab. Target FoS 1.8.
Three-setup part on the CNC mill using soft jaws as part of the assembly.
AISI 4130 steel, 0.25 in tab thickness. From the cost report drawings and CAD: From the cost report drawings: AISI 4140 Steel (CR26I_FrontUpperBearingHolder).
Fault Vault, CR26I, Potential Failure: upper arm ball joints became loose within the housing and had vertical compliance. Theory is that the bearings are being staked with too much force. CR25 had a separate retention failure caused by an improperly designed chamfer in the holder.
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. CR26I_FrontUpperBearingHolder (mm): TRUE R7.9, TRUE R15.7, R2.4, R8.8, 70.3, 57.7, 33.7, 9.5, 22.2 Source: Cost report drawings: CR26i/Suspension/Competition/Cost Report Drawings/Suspension and Shocks/Front A-Arms/CR26I_FrontUpperBearingHolder.pdf Quantity per car, as costed: 2
Nothing in CrimsonStorage covers these yet.