Cornell University

Cornell Baja SAE Uses MSC ADAMS/Car for Suspension Design

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The Cornell Baja SAE team utilizes ADAMS/Car to analyze suspension kinematics and performance. ADAMS/Car assists in understanding the motion characteristics of suspension such that the designer can make informed decisions to improve vehicle performance.

Figure 1: ADAMS/Car assemblies

Off road vehicles pose an interesting design problem for engineers. Long travel suspensions and low wheel rates introduce many design difficulties regarding handling and driver interaction. ADAMS has the tools to provide the necessary information to ensure the vehicle is predictable and maneuverable during driving. Baja SAE vehicles are underpowered by requirement, and it is the job of the suspension designer to incorporate limit oversteer characteristics while maintaining low speed, kinematic cornering capability. Analyzing wheel motion gives invaluable insight during design.

Roll stiffness and roll center migration are of primary concern during design. The ratio of front to rear roll stiffness controls the onset of oversteer. ADAMS/Car simulations generate the necessary information to analyze suspension motion in roll.

Figure 2: Roll center migration in roll output

Minimization of roll center migration in roll creates a vehicle that is far more predictable under demanding driver input. Wheel camber is also another parameter that can be varied to increase the likelihood of oversteer. The Cornell team has employed high amounts of caster angle on their front suspension in order to achieve large front camber angles during cornering, increasing lateral force generation at the front tires. Yet again, motion analysis with ADAMS allows a deeper understanding of the steering characteristics of the vehicle.

Figure 3: Wheel camber during steer

One identifying feature of all Baja vehicles is the amount of suspension travel – over twice that of typical passenger cars. With long travel suspension, special attention must be paid to how the tire is moving across the ground during travel. Since Baja SAE vehicles are severely power limited, any inefficiencies present by tire scrubbing will act to drastically slow the vehicle down. Half-track change in wheel travel becomes a primary concern, and must be effectively minimized. ADAMS/Car allows comparison to past suspensions and permitted the reduction of rear suspension track-change.

In the future, the Cornell Baja SAE team hopes to construct a full vehicle model in order to understand body pitching over various terrain features such as jumps and large drops. Many current Baja vehicles suffer from a “nose down” characteristic while airborne, which prevents the vehicle from being driven at maximum speed over aggressive terrain. Other potential future uses of ADAMS on the Cornell team include exploiting the design of experiments (DOE) tool and developing durability load cases for the entire vehicle.