Take torque from the chain into the differential.
A 40-tooth aluminium sprocket bolted to the sprocket mount on the differential.
An off-the-shelf Vortex sprocket replaced in-house machined 7075 aluminium sprockets. The stock for the in-house part cost roughly $80 against $68 for the Vortex sprocket, and buying it reduced manufacturing time by 3 hours.
CR22 static analysis: inner faces of the flower petal fixed, bolt holes as roller/slider constraints, bearing loads of 125 lb, 482 lb, 987 lb and 1,246 lb applied left to right. Maximum stress 48.32 ksi against a 73.244 ksi yield for 7075-T6, minimum factor of safety 1.516, maximum displacement 0.00798 in at the tip of the tooth behind the highest force.
Four setups. Mill, setup 1: bore the centre of the round aluminium plate so the stock can be faced on the lathe. Clamp the stock to the table on top of another aluminium plate. The bore goes completely through. Lathe, setup 2: face one side flat. This is the final finish on the underside of the sprocket, so surface finish matters; remove as little material as possible. Mill, setup 3: drill the holes that mount the stock to its workholding, using the bore to locate the origin. Mill, setup 4: final operation on the sprocket workholding. Leave stock and clearance the inside of the flower petal using the flower petal on the spool. The fit must be snug or the mounting bolts end up loaded in shear and will fail on the car. Bolts have to be removed from the workholding to let the machine cut, but keep three bolts tight at any point.
Vortex aluminium. From the cost report drawings and CAD: From the cost report drawings: 7075 Aluminum (Vortex 40T Sprocket - 435).
Fault Vault, 2026-07-12, CR26I: the chain did not fit the machined sprocket during testing, from either excess stock left during milling or a misunderstood centre-to-centre analysis. The corrective action is to verify the machined sprocket on the centre-to-centre checker and to test fit on the car in the shop before going to the track.
40 tooth, 520 pitch. 6.30 in centre-to-centre distance to the front sprocket. 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. 40T Rear Sprocket (Vortex) (mm): 210.60, 5.08 Rear Sprocket (spool) (cost report) (mm): 210.60, 9.84 Vortex 40T Sprocket - 435 (as drawn): 5.88, 0.59, 10.001.00, 55.00, R5.50, 209.33, 20.93 Source: Cost report drawings: CR22/Powertrain/Design/X - Cost Report Drawings/Drivetrain Assembly/40T Rear Sprocket (Vortex).pdf; CR22/Powertrain/Design/X - Cost Report Drawings/Drivetrain Assembly/Rear Sprocket (spool) (cost report).pdf; CR25/Powertrain/Design/Y - Cost Report Drawings/Drivetrain/Vortex 40T Sprocket - 435.pdf; CR26i/Powertrain - IC/Design/Y - Cost Report Drawings/Drivetrain/Vortex 40T Sprocket - 435.pdf and 1 more Quantity per car, as costed: 1
Nothing in CrimsonStorage covers these yet.