The Queen’s University Solar Vehicle Team performed a linear static stress analysis of their solar car’s wheel using ALGOR software. Based on the analysis results, the team decided to change the inner wheel design from the original 5-spoke design shown here to a 3-spoke design for the two front wheels.

  
QUEEN’S UNIVERSITY SOLAR VEHICLE TEAM SELECTED ALGOR FEA AND SOLID EDGE

The American Solar Car Challenge is the longest solar car race in the world. For ten days in July 2001, 40 university teams traveled nearly 2,300 miles along old Route 66 from Chicago, Illinois across the Great Plains, Rocky Mountains and Great American Desert to the finish line in Southern California. Among the accomplishments achieved by the race participants was the incredible comeback by the Queen’s University Solar Vehicle Team of Kingston, Ontario, Canada from fourteenth position to finish fourth. The American Solar Car Challenge was the first race for Mirage, the eighth solar car designed and built by the Queen’s University Solar Vehicle Team and the first to use ALGOR finite element analysis (FEA) software in its design. FEA was used to optimize the wheel design for weight reduction while maintaining structural performance. 

The Queen’s University Solar Vehicle Team is a multidisciplinary team of students and faculty who volunteer time and energy to design, build, promote and race a vehicle powered entirely by the sun. There are approximately 100 undergraduate students who are involved with the team during the school year, 20 of whom continue during the summer as the race team. The FEA software used by the Queen's University Solar Vehicle Team was granted to them as part of ALGOR’s ongoing efforts to support academic engineering competitions.

Queen’s University’s Mirage had big shoes to fill; its predecessor, Radiance, was officially recognized by the Guinness Book of World Records as holding the record for “Furthest Distance Traveled by a Solar Car in One Journey” (7,044 km) and came in 2nd at Sunrayce ‘99 (Washington DC to Orlando). Like Radiance, Mirage has an aerodynamic airfoil-shaped body and a high-efficiency solar array. A carbon fiber monocoque chassis (similar to that used on Formula One race cars) is used because of its light weight and stiffness. A custom-made steering system is employed to allow all components to fit inside the thin body of the car. Energy is stored in a Lithium Ion battery because of its light weight and high efficiency. The team has also designed an electronic network to control the vehicle's telemetry and electrical systems. 

To increase efficiency and stability, Mirage was designed to travel on three magnesium wheels rather than the four aluminum wheels used with Radiance. Using three rather than four wheels reduces rolling resistance, reduces weight and increases the stability of the solar car. The switch from aluminum to magnesium for the wheel further reduces weight. However, magnesium is not as strong of a material as aluminum. Therefore, simulations had to be done to make sure that the wheel design would withstand the stress of cross-country racing with the different material.

David Valletta, a Queen’s University engineering student and the Mechanical Systems Manager for Queen’s University Solar Vehicle Team, built a computer-generated solid model of the wheel in Solid Edge by UGS and then captured the model for analysis using ALGOR’s InCAD technology. An automatic hybrid mesh consisting of approximately 25,000 tetrahedral elements was created. “When I started this project, I had never used ALGOR software,” said Valletta. “I found InCAD to be easy to use and learn. To get started, I used the InCAD/Solid Edge tutorial provided with ALGOR software and a few of the free online Webcasts, all of which were very helpful.”

Valletta decided to perform a linear static stress analysis on the wheel because he had limited time in which to perform the wheel design and needed to keep the design well within the yield point. “I didn’t have the time or resources for a lot of prototype testing of a design that wasn’t a little ‘over built,’” said Valletta.

The model of the wheel was loaded to simulate the basic automotive bump, turn and brake loads. For all parts designed for the car, the team assumed a 3g bump, 0.8g turn and 0.5g brake load. Those loads were applied simultaneously to the base of a spoke and to the rim between spokes. Fixed boundary conditions represent a rigid attachment of the wheel to the hub; thus, the wheel took up the entire load.

After the analysis was completed, von Mises, maximum and minimum principal stress and displacement contours were reviewed and the team decided to change the wheel design. “The analysis output was very easy to view and therefore it was easy to explain to the team what was happening in my analysis,” commented Valletta.

Valletta then varied the thickness, width and number of spokes over the course of five models until an acceptable balance was reached between mass and safety. The original design was for a 5-spoke design. “Through FEA, we arrived at a 3-spoked design with a smaller hub for the front wheels and a 5-spoked design with a larger hub for the rear motor wheel,” said Valletta. “Over the years, the team has observed that the motor wheel experiences some strange forces and vibrations so this design needed to be different.”

Mirage is the eighth solar car designed and built by the Queen’s University Solar Vehicle Team and the first to use ALGOR finite element analysis (FEA) software in its design. Mirage has an aerodynamic airfoil-shaped body, a high-efficiency solar array and a carbon fiber monocoque chassis (similar to that used on Formula One race cars).

Although the team did not perform any laboratory prototype testing, the wheels endured a tougher test while racing. During the American Solar Car Challenge race, the car went off the road into a ditch. “The suspension was destroyed, but we were amazed to see that the wheels were not damaged,” said Valletta. “We were very happy that we had completed the FEA analysis on the wheel design. Fortunately, we were able to repair the suspension that night and continue racing later the next day.”

The team has plans to use ALGOR for their 2003 car. “New wheels will be designed for the 2003 car and I hope to have time to create several additional simulations, most likely using Mechanical Event Simulation,” said Valletta. “Other materials may be used. The team may venture out and design a composite wheel, which would use ALGOR software in even more depth.”