20XT Suspension Design

Johns Hopkins University- Baja SAE Team 2023

Overview: As suspension lead for the 20XT, I focused on the following to improve performance and streamline the design process:

Improve on previous analysis methods including developing a load propagation spreadsheet, creating more realistic FEA models and Neuber stress correction to allow for increased weight reduction and less conservative analysis
Integrate team-wide goal of loaded halfshafts, raising ground clearance and reducing weight
Creation of first ever 5-axis CNC Front and Rear Upright, transition from welded plate steel
New jigging methods to account for tighter tolerances on linkages

Highlights:

Suspension Loads Spreadsheet:

Developed and streamlined a spreadsheet to take measured loads and suspension geometry to determine the loads at each point for every linkages to use in FEAs:

FEAs: Analysis of each linkage was derived from these loads; full assembly analysis was used to simulate bushing compliance and shock reaction accurately

Neuber Plasticity Corrections: A Neuber correction was used to account for the conservatism in the linear analyses performed, and allow for lighter components

Loaded Half Shafts:

Unlike in previous years, where the rear axle has plunge and both an H-Arm and camber link are used to constrain suspension, the loaded half-shaft suspension of the 20XT transfers suspension loads through the axle. This gives increased ground clearance and decreased weight but come in increased risk with an exposed rear axle and increased loading on the H-arm and Transfer Case.

19XT Rear Suspension 20XT Rear Suspension

The rear hub and upright design and analysis changed significantly due to the switch to loaded half-shaft; Now having to consider the reaction forces provided by the half-shaft, creating a complex loading condition

5-Axis CNC Uprights

A fun new challenge this year is designing uprights with the consideration for 5-axis machining that we were able to get sponsored, and gaining the weight savings from switching from steel to aluminum, losing 2lbs across the vehicle.

Improved Jigging:

With tighter clearances than ever this year (the upper A had to be bent for the first time to allow room for the tie rod), we needed to ensure the linkages would be welded with minimal to now warping due to heat, so I improved on our previous iteration of linkage jigging to incorporate shaft collars to fully constrain our linkages throughout the welding process.

The new methods helped save significant time welding, cutting total weld time (set up, welding, letting part cool, etc. ) for linkages in half, from 6 weeks last year to 3 weeks this year

I didn't get to weld all the linkages, mostly spending my time setting the jigs up for someone else to weld, but I got to weld a few of the H-arms (pictured above)

Results:

The complete suspension assembly. Overall, the manufacturing and welding processes went smoothly and quickly, with every component able to be finished in the 3 week time frame we set out for ourselves. The completes suspension weighs ~24lbs which is 4lbs lighter than the previous year's iteration.