Rear Subframe Redesigned and Ready for Fabrication

We have officially completed the redesigned rear subframe, which now meets the EcoCAR 2 requirements for stress and strength factors of safety.

“The redesigned rear subframe is important for a couple of reasons,” said mechanical subteam member Chris Eaton. “First, it contributes to the overall safety of our vehicle by providing structural strength and stability. Second, the redesigned rear subframe allows us to completely package our rear powertrain which is required for all modes of operation.”

While the redesigned rear subframe is just as stiff as the previous model, it is twice as strong. To achieve this, our mechanical subteam had to first determine which locations on the subframe needed the most support and where they needed to add reinforcements. Next, we had to identify which shape or geography would best fit the design criteria. Finally, we performed the required finite element analysis (FEA) to accurately represent the stress and displacement generated within the subframe while under different types of loading. 

Three stages of the redesigning process.

The finished product includes two major modifications from the original. First, we changed the angles at which the front cross member approaches the rest of the subframe from 90° to roughly 140°. This reduces stress. Second, we added a new arching cross-member, which will assist with load distribution across the rear portion of the subframe.

In addition to successfully developing a redesigned rear subframe that meets both competition and team (HEVT) requirements, this project also provided a great chance to learn.

“I have learned an immeasurable amount about the modeling, drafting, and simulation aspects of computer-aided design (CAD),” Eaton said.

We also learned about how a product moves through the design, fabrication installation phases. While working on the subframe, we reached out to professional engineers at companies like GM and Siemens, which was a great opportunity to learn and network.

With the redesigned rear subframe complete, we can now focus on testing the exhaust system to ensure that it does not leak. We will also be working on the refinement and installation of components associated with our fuel system.

“I look forward to seeing how the rest of the semester unfolds and how we favor during competition this summer. I believe that we can place well in competition if we finish out the rest of the semester on a strong note,” Eaton said.

Do you think our new design will work well at final competition? Let us know in the comments below!

#TransformationTuesay with Mary's Rear Wiring Harness

Mary the Malibu has been busy getting herself dolled up for competition lately. 

The team has been working hard on a new trunk wiring harness. Although the wiring has been functional, it was extremely disorganized and made it difficult to diagnose faults. Since we are in the refinement phase of EcoCAR 2, some of our team members suggested that something be done to clean up the wiring for serviceability, consumer acceptability also weight reduction. 

The majority of the old wiring was 20 AWG (american wire gauge) wire with thin-walled insulation. Most of the wiring in the trunk is used for signal transmission - not power - so a smaller gauge wire can be used for these connections. We purchased seven rolls of 22 AWG thin-insulation wire to replace the signal wires to reduce weight and take up less space in our trunk.

Before and after of Mary's rear wiring harness.

"I created an entirely new harness so that wire lengths could be measured away from the car," said controls subteam member Brandon Nash. "This was so I didn't interrupt the work others were doing with other parts of the car. I then created new pin-outs for every connector in the trunk as well as connectors required to make the harness fully removable." 

Once the pin-outs were up-to-date, we started to lay wire for the new harness. The final result is a smaller, lighter and entirely removable rear wiring harness. As we continue preparing Mary for final competiton, we will be able to add new wires and run them through the loom to keep them organized and as short as possible!