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Bradley University Formula SAE - Suspension Team The 2012 Bradley University FSAE vehicle utilizes independent front and rear suspensions with SLA wishbone geometry. Fox Racing VAN RC concentric coil spring shock absorbers are pushrod actuated. They have adjustable damping from 0-8.5 (lbf•s)/in and adjustable spring preload. The A-Arms consist of .625 inch OD 4130 Chromoly tubing with .049 inch wall thickness. The tubing is welded to collars into which spherical bearings are pressed, with the bore axis oriented vertically. This results in the highest loads on the bearings acting radially, which is the ideal design condition. It was necessary to plan the suspension mounting tab spacing and collar size to allow for at least 1 inch of suspension travel in each direction as indicated by the FSAE rules. Spherical bearings were used at the ball joints rather than rod ends in order to avoid having rod ends in bending. Instead, camber is adjustable through the use of camber plates mounted to the upright.
The uprights are cut from 6061 T651 Aluminum through a waterjet procedure. Finish machining was performed on a CNC mill. The uprights are mirrored on the right and left sides, and vary from the front to the back due to differing ball joint locations. Brake caliper mounts are incorporated into the upright deign, with the calipers oriented such that bleed valves are oriented vertically to ensure effective brake bleeding. The mounts are also designed for easy caliper removal, simplifying assembly of the braking components. Pro/Engineer Mechanica was used to perform static and fatigue analysis on the uprights. Forces considered include cornering, braking, and bump loads.
The tires on the car are 20.5 in x 7.0 in – 13 in R25B Hoosier racing slicks. They are mounted to three-piece aluminum rims with 27-tooth spline centerlock hubs. The hubs fit onto 6061 T6 aluminum spindles. The spindles are press fit into double row angular contact ball bearings retained in the upright by a press fit, lip, and retaining ring.
Wilwood braking components are used on the 2012 Bradley University FSAE car. Dual .625 inch Wilwood Compact Remote Master Cylinders create independent front and rear braking systems controlled by a Wilwood bias bar. The calipers are opposing single piston Wilwood calipers. In the front, the piston area is 2.4 in2, and in the rear, the piston area is 1.5in2. Wilwood Polymatrix A compound brake pads are used in the front and rear. The brake rotors were student-designed. The material selected was Durabar G2 Gray Cast Iron due to excellent thermal expansion, thermal conductivity, wear resistance, and frictional properties. The rotors are 10 inches in diameter with a 0.2 inch thickness. Thermal, static, and fatigue analysis was performed using Mechanica. Waterjet cutting and Blanchard grinding were used to fabricate the rotors. For production, the rotors could be easily cast and finish machined.
The steering system utilizes the concept of Ackermann geometry. The Ackermann steering geometry is fully adjustable with an interface at the upright to remove and replace Ackermann tabs. The rack and pinion chosen has a gear ratio of 6.4 to 1 with an overall travel of 4.5 in. The rack and pinion is able to complete the full travel length with a 7/8 turn of the pinion gear. This allows for the driver to keep their hands on the wheel at all times. Steering shafts will be connected with a single u-joint that has an allowable shaft angle of 35°. This is achieved by placing the rack in a front steer position. This year the Team is composed of: Trevor Blough (Team Captain) Payton Haight Bryce Randall Tyler Smith |
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