SunRayce N’Energy Car Suspension Analysis
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SunRayce is a nation wide
competition that allows college teams to design, build and race solar
cars. The Northwestern Solar Car Team
built a car that competed during the summer of 2001. Currently the team is preparing to build
the second-generation car, improving on previous efforts. The team asked our group to assist them by
collecting data on the forces of the suspension. With this information, a future design can be optimized for
lighter weight. As
the car drives, various forces act on the wheels of the car. These loads are created by bumps or other
imperfections in the road and by acceleration of the car. The former primarily produces forces that
are normal to the road surface, and the latter produces forces that are
primarily tangential to the road surface.
Knowing the normal forces on the wheel will tell you the maximum
tangential forces on the wheel.
Therefore, the magnitude of the normal forces on the wheel is of
primary interest to the solar car team.
To the left, a student is shown attaching the strain gages to the
shock under analysis.
Here, the strain gages are seen close up after being mounted in a
Wheatstone bridge. SunRayce requested us to find the strain on the
shock under various conditions so that they might use the data to better the
car's suspension design. With this in mind we ran tests under various
conditions. The testing conditions
were chosen to closely model a variety of situations that the car might
encounter during competition. Since
our setup was complete to the point where the only thing we needed to do was
run the LabVIEW program (at right) and drive the car, the program was run
while the Solar Car was driving in the following scenarios: 1.1. Straight down a smooth road 2.2. Turning left on a smooth road 3.3. Turning right on a smooth road 4.4. Straight down a bumpy road 5.5. Running over a pipe
.5'' diameter In each of these situations, care was taken that car
speed, weather conditions and other factors were kept as constant as
possible. TO VISIT SUNRAYCE’S HOME PAGE,
USE THIS LINK: http://www.sunrayce.northwestern.edu TO RETURN TO THE ME HOME PAGE,
USE THIS LINK: |
Shown here is the entire experimental setup including a wheat stone
bridge of strain gages and a potentiometer with a custom bracket to measure
displacement. In accordance with this, the purpose of this
experiment was to determine the magnitude and frequency of forces acting on
the front suspension of the solar car.
To do our experiment, we utilized each of the tools learned in the ME
224, Experimental Engineering course, from LabVIEW computer programming to
circuit setup. Our experiment will improve the SunRayce vehicle and hopefully
contribute to a strong Northwestern finish at this year's competition.
Above is a diagram of the LabVIEW coding used to collect data from
the shock.
Data analysis revealed that the solar car was of robust design. Several calculations were conducted to
determine the fatigue, yield and impact limits. The existing design exceeded all requirements with some safety
factors of up to 60 times the expected loads. As might be anticipated, impact loading had the lowest safety
factor. Future designs should aim to
push these safety factors to much lower levels, as excess weight is the
greatest consideration. Other
material choices such as aluminum or magnesium alloys could provide the
necessary strength without sacrificing weight. |
Produced by Alexander
Ellis, Ian Harrison, Lars Moravy, and Jonathon Walker – December 2001 – Prof.
Espinosa, ME224