Mechanical Engineer
Suspension
Packaging
About Baja SAE:
Baja SAE is an intercollegiate design competition run by the Society of Automotive Engineers (SAE). Teams of students from universities all over the world design and build small off-road cars.
Design Goals:
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Robust design (FOS > 1.5)
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Lightweight (Lighter than 2020's car)
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Compact (1/4 inch clearances)
Design Matrix:
A design matrix was created in order to decide which suspension type was going to be used. After hours of discussion, we decided to create a rear suspension with a camber-link and H-arm.
Force Calculator:
In order to analyze the wheel hubs and uprights, a force calculator was created. This calculator took into account different load scenarios such as:
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Acceleration
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Braking
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Cornering
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Frontal impact
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Rear impact
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Lateral impact
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Dropping
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Hitting a log
Generative Design:
Generative design and topology optimization functions from Fusion 360 and SolidWorks were used in order to optimize the weight of the wheel hub and upright without compromising their strength.
FEA:
To verify that the parts would support the forces calculated on the force calculator, and no extreme deflections would cause the parts to fail, a Fiinite Element Analysis (FEA) was performed using SolidWorks' static simulation function.
Upright
About the upright :
The upright was designed to be lighter and tougher than in past year's. This component of the car experiences forces of great magnitude, so several simulations in generative design and FEA were done before finalizing the model. The clearances for the bearing, and the CV joint were a challenge that had to be overcome. The result is a tough upright that was never broken or replaced during competition. Also, the weight of the upright was almost half of past year's car, fulfilling one of our main focuses in the design matrix.
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Material: Aluminum 7075
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Manufacturing Method: 3-axis milling machine
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Weight: 2 lb
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FOS: 1.5 (worst case scenario simulated)
Wheel Hub
About the wheel hub :
In past years, the wheel hub was always problematic and caused the car to be unable to compete, so my focus was centered on fixing this problem. Over 40 simulations were performed before the final model was created. This wheel hub is extremely light, thin, compact, stiff, and was never replaced or broken during testing or both competitions.
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Material: Aluminum 7075
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Manufacturing Method: 5-axis milling machine
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Weight: 0.84 lb
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FOS: 1.88 (worst case scenario simulated)
Wheel
About the wheel :
The wheel size was first chosen by working with the geometry suspension team. Based on vehicle dynamics, a 21 inch wheel was picked for the rear which made our car safe but also agile. This component of the car was one of the main priorities, since it could affect the upright, wheel hub and axle sleeve size.
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Material: Aluminum 6061
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Manufacturing Method: Bought
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Weight: 3.34 lb
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FOS: N/A
Bearing
About the bearing:
The wheel bearing was picked based on past experience. Since the deflections and angle of deflections are negligable, the wheel bearing was bought from a supplier. This bearing used a bearing c-clip to stay inside the upright and was press fitted.
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Material: Steel
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Manufacturing Method: Bought
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Weight: 0.7 lb
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FOS: N/A
Axle Sleeve
About the bearing:
The axle sleeve is one of the most important components in the rear suspension packaging, since it is what transfers the rotation from the axle to the wheel hub. This axle sleeve was manufactured with precision and accuracy, so the press fit between the sleeve and the hub was perfect. The sleeve was never replaced or broken during testing or both competitions, and the slip between the wheel hub and the axle sleeve was minimal.
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Material: Aluminum 7075
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Manufacturing Method: Lathe and milling
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Weight: 0.11 lb
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FOS: 2
Final Assembly
The final assembly successfully satisfied all design requirements for competition. In addition to this, the assembly was several pounds lighter than assemblies from the past.
Manufacturing and Results
Both the wheel hub and the upright were manufactured in a CNC. A mill and lathe were used to create chamfers, holes, and grooves on the upright and axle sleeve. The parts were tested several times and never broke, bent, or fractured. As a result it was never necessary to change them in both competitions (Arizona and Louisville).
