Mechanical Engineering Department
BS in Mechanical Engineering
The purpose of this project was to design a suspension that would improve the performance of the Cal Poly SAE Formula Electric car around a racing track Performance would be quantified through skidpad, slalom, and straight-line acceleration tests as well as autocross lap times. The approach to meeting the objective was to increase the steady-state lateral acceleration and quicken the transient response while maintaining predictable handling so that the driver could extract maximum performance from the car.
The car uses round-section (motorcycle) tires at a large negative camber angle because the lateral force generated by a pair of negatively-cambered tires increases with lateral load transfer, which is opposite of the behavior of normal car tires. According to research, maximum lateral grip is achieved at a high-negative camber angle (-40 degrees) but best longitudinal acceleration is had with no camber.
The original design for the suspension was a passive, dynamic camber system which varied the camber in order to provide maximum grip in a straight line as well as in turns. The scale of this design was deemed to be too large for the time, resources, and manufacturing skill of the Formula Electric team this year. Therefore it was decided to produce a highly adjustable static camber suspension that could be tuned best performance as well as adjusted to allow for testing of the dynamic camber concept.
The final design is a static camber system using the “five link” suspension configuration in both front and rear. The links have turnbuckle adjustment and are easy to manufacture so that many camber angles can be tried in order to find the optimal camber angle for a particular track. The uprights are of shell construction and the rear uprights can be used at any camber angle. The front requires a slightly different upright geometry for very large camber angles than for small camber angles. Tires are sized 100/85-R10 on all four corners and are meant for small racing motorcycles. They are lightweight and allow large camber angles to be used.
Component testing and validation consisted of Instron testing for link buckling, link thread pullout, link tensile strength, and rod end buckling. Testing on the suspension as a whole will involve skidpad tests to find the maximum steady state lateral acceleration from various camber configurations as well as acceleration tests to find the effect of camber on longitudinal acceleration. The goal will be to find the best static camber setup and determine if a dynamic camber system, active or passive, would actually provide a significant advantage if the manufacturing resources were available to build it.