Split drive torque between the rear wheels while allowing them to turn at different speeds, with a tunable lockup characteristic.
A Drexler FSAE adjustable differential. Preload is set through clutch packs, and the acceleration and deceleration lockup curves are set by ramp angle, so the differential's behaviour can be adapted to driver preference and track conditions.
Chosen over a spool with the trade stated explicitly. Advantages: tunable preload for quick adaptation, adjustable acceleration and deceleration lockup curves, better reliability than custom implementations, better drivability than a spool, and a consistent driving style over extended testing sessions and endurance events. Downsides: roughly 9 lb heavier than the previous spool implementation, $4,204 against $362 for the spool assembly, and more points of failure including leaky housing seals, drain plugs and stub axle seals.
Must be easily removable so the differential can be tuned. This drove the non-adjustable fixed-pin carrier design.
The CR26I goal was to validate the differential selection through on-track testing and analysis, to confirm the performance benefit offsets the added weight against lighter options.
Purchased Drexler unit. Castrol Syntrax LSD Fluid 75W-140.
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.
From the Sphinx wiki differential page: - Settle the spool against the Drexler on data rather than preference. Compare lap times and corner exit speeds for the open differential and for the Drexler at several preload levels including fully locked; if fully locked is not noticeably slower, weigh what a spool costs in money and in team workload. - CV joints are named as the place to cut rotating mass. A code for it already exists; acting on the result would need a wire EDM sponsorship. - No weight reduction target is set for the differential. Further loading and fatigue analysis is needed before one can be, so the stated target is no weight increase.
Setup: preload 65 Nm for Autocross and Endurance (86.7% of range), 55 Nm for Skidpad (73.3% of range). Ramp angle 60 deg acceleration / 45 deg deceleration. 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. Drexler (as drawn): 8.00, 0.80, 7.65, 0.76, 44.00, R4.40, 50.00, 5.00, 13.60, 1.36 Source: Cost report drawings: CR25/Powertrain/Design/Y - Cost Report Drawings/Drivetrain/Drexler.pdf; CR26i/Powertrain - IC/Design/Y - Cost Report Drawings/Drivetrain/Drexler.pdf; CR27i/.Powertrain/Design/Y - Cost Report Drawings/Drivetrain/Archive/Drexler.pdf Quantity per car, as costed: 1
Nothing in CrimsonStorage covers these yet.