Jacking Bar

overview

This jacking bar was redesigned from scratch for the University of Alberta's Formula SAE team after the previous year's bar didn't meet FSAE regulations. It's the lifting point the pit crew uses to raise the car during pit stops, and since it mounts to the drivetrain, it had to support the car's weight while clearing all of the surrounding components. I designed the bar and its mounting tabs in SolidWorks around the FSAE rulebook's requirements, validated the design with FEA, and fabricated it from steel tube by milling, angle grinding, and MIG welding. The final bar came out 30% lighter than the previous year's while maintaining a minimum factor of safety of 2.0.

Design decisions and challenges

• Designed the bar around the FSAE rulebook's requirements for load capacity, attachment geometry, and clearance, since the previous design hadn't met them.
• Explored several geometries to find one that mounts cleanly to the drivetrain without interfering with the components around it.
• Used FEA to identify low-stress regions of the tube and removed material there with scooped cutouts, filleting the edges of each cutout to reduce stress concentrations.
• Applied DFMA principles so that every feature could be manufactured with the tools available in the shop.
• Produced fully dimensioned drawings for the bar, the mounting tabs, and the full assembly, so the part could be fabricated directly from them.
• Cut the cutout profiles by hand using a stencil to guide the angle grinder, then sanded the edges to match the model as closely as possible. Hand cutting can't be perfectly accurate, but combining the stencil with careful finishing produced a clean result.

What I learned

Stress concentrations are critical on a part like this, and they need to be accounted for at every stage of the design, from the CAD model to the fillets to how the part is actually cut. I also learned how important it is to design for manufacturing and assembly when a part sits inside a much larger assembly, since every feature has to be buildable and clear everything around it.