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We design, fabricate, and compete with small formula-style racecars against other colleges from around the world, testing our engineering skills and creativity.
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December 2, 2013
We have been working hard on our detailed design this past month. I got two leads, Gordon Peng (Composites) and Matt Dethlefsen (Drivetrain) to share what they’ve been working on this past month.
Here’s what Gordon has to say about B14′s bodywork:
The design for the bodywork of our upcoming FSAE vehicle is an iteration of last year’s design. Key changes include more reliable fastening mechanisms, as well as a more organic and fluid shape while keeping weight and correlated cost low. One of the challenges that appeared in the design process this year was the migration of the front-upper-forward suspension node outward, which resulted in a substantially thicker mid-section of the nosecone if we were to cover it. Not only was this design deemed quite unattractive by numerous members and advisers of the team, it would have also increased weight and material cost, not to mention the extra efforts needed to mold and manufacture the part. Instead, the solution was to allow the bodywork to cut into the front tube structure, leaving part of the front section of the vehicle chassis exposed, but still maintaining rules compliance and a more acceptable aesthetic appearance.
Matt Dethlefsen, Drivetrain Lead, has been working on flex discs for B14:
When it was determined that pulling weight out of the drivetrain was going to be critical to meet our performance specs with a small engine, the CV joints and half-shafts became an interesting topic of discussion. After much debate, a flex disc design with carbon half shafts was pursued and was expected to save about 6 pounds overall. The hardest part of this design was the flex disc CV joints as they have never been done by our team and the resources available from other teams that have run them are scarce. I ran initial FEAs in order to determine the stresses that would be seen in the parts, but the setup was rather complex and due to the small, complex geometry of the flex discs, the time spent running FEAs made them slightly less useful. Thus, over the course of a weekend, I developed a MATLAB function that simulated the bending, torque, and elongation stresses seen in the discs based on the input torque, suspension deflection, and stress risers. This function was used to iterate through various designs and materials and eventually the geometry and material was finalized.
FEA of a flex disc
As this type of analysis had never been done before, we wanted to validate our simulations. We used a strain gauge to pull out the actual bending and elongation stresses and they matched within 15% of what our simulation predicted (the prediction was conservative, as designed). After the static tests were complete, we ran a dynamic fatigue test on a lathe that demonstrated the discs would survive a minimum of 10 hours of testing under very non ideal conditions (rusted discs, increased stress risers, non-concentric holes). Also, the dynamic test showed that the failure mode was not instantaneous and thus we can monitor the condition of the discs and replace them before failure. We are now waiting on new discs to be laser cut and will continue testing under ideal conditions to produce more data that backs up our current results before putting them on the car.
Flex disc testing on the lathe
Flex discs after fatigue testing and failure
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