CR21 assembly line covering the sprockets and mount.
Superseded by the Drivetrain Assembly grouping.
No part-specific design process is documented. The DriveTrain subsystem design process applies: 1. Set gearing from the tractive force diagram, top speed and the event speeds actually seen (autocross top speed 69 mph, endurance 72 mph, gear-limited top speed 82 mph). 2. Design the carriers non-adjustable with a fixed pin, integrated with the engine pins, to reduce assembly complexity and failure points and remove the need for weld-on carrier mounts on the frame. 3. Analyse the carriers at acceleration and deceleration load cases with a 2.0 shock loading factor. CR26I LH carrier at 39 lb-ft with shock: 32.949 ksi peak von Mises, minimum FoS 1.211, 0.013 in average axial bearing bore deflection. RH carrier: 9.432 ksi, FoS 4.229, 0.001 in. 4. Set the half shaft length with a custom measuring jig so the tripod travel range cannot be exceeded, then groove for retaining rings. 5. Validate on track and by inspection of the wear surfaces after testing.
One hard geometric constraint drives the design: at peak loading, deformation must be no more than 0.0125 in measured from the centre of the front sprocket. The reason is frictional loss. Torque from the engine applied to the differential pushes the assembly away from concentricity, and off-concentric running raises drivetrain friction. The source requires this limit to be demonstrated with FEA rather than assumed. The wiki source does not attach a car generation to this constraint, so it is not confirmed as CR21-specific.
Sprocket FEA is documented as a load case. The result plots exist only as images in the wiki source, so the setup below is recoverable but the resulting stresses are not. - Loading: bearing loads along the teeth, left to right, of 1246.13, 987.82, 482.71, 142.54 and 25.99 lbf. - Fixed: the washer bolt holes, plus a hinge along the flower petal insides. - Yield: 73 ksi. - Material: 7075-T6 aluminium. The acceptance criterion for the analysis is the concentricity limit in Design Constraints: no more than 0.0125 in of deformation from the front sprocket centre at peak loading. The source names a section for gear stress equations but leaves it empty, so no hand calculation is recorded alongside the FEA. One validation route is proposed and not reported as done: attaching strain gauges to the differential carriers, which the source offers as a way to check this design against the analysis.
From the cost report drawings: Alloy Steel (11T Front Sprocket Drawing); Steel (Front Sprocket).
None recorded. This part has no entry in Knowledge_Transfer/Issue Logging/Fault Vault.xlsx, in either Issue Log.xlsx, in CR22/Issue Tracking/Shakedown 7-15-23.xlsx, or in any design review issue list found in CrimsonStorage or Box.
CAD mass, CR26I master assembly: 0.102 lb (0.046 kg). CG at X 77.06 in, Y -4.84 in, Z 10.77 in in vehicle coordinates. (CAD component: Sprocket) CAD mass, CR25 master assembly: 0.102 lb (0.046 kg). CG at X 77.06 in, Y -4.84 in, Z 10.77 in in vehicle coordinates. (CAD component: Sprocket) CAD mass, CR22 master assembly: 0.102 lb (0.046 kg). CG at X 77.06 in, Y -4.84 in, Z 10.77 in in vehicle coordinates. (CAD component: Sprocket) 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. 11T Front Sprocket Drawing (as drawn): 33.25R3.32, 25.40, 2.54, 65.38, 6.54, 13.39, 1.34, 5.77, 0.58 11T Front Sprocket (mm): 13.39, 66.05 Front Sprocket (as drawn): 20.32, 2.0333.25, R3.32, 13.39, 1.34, 5.77, 0.58 Source: SolidWorks mass model exports: CR22 (5 May 2024), CR25 (4 Jul 2025), CR26I (30 Jul 2025), CR26E (22 Mar 2026) | Cost report drawings: CR22/Powertrain/Design/X - Cost Report Drawings/Drivetrain Assembly/11T Front Sprocket Drawing.pdf; CR22/Powertrain/Design/X - Cost Report Drawings/Drivetrain Assembly/11T Front Sprocket.pdf; CR25/Powertrain/Design/Y - Cost Report Drawings/Drivetrain/Front Sprocket.pdf; CR26i/Powertrain - IC/Design/Y - Cost Report Drawings/Drivetrain/Front Sprocket.pdf and 1 more Quantity per car, as costed: 1
Nothing in CrimsonStorage covers these yet.