Formula SAE Steering System

Each school year, MIT Motorsports designs, builds, and competes against other universities with a formula-style car in the Formula SAE competition series. My second year on the team (2015-2016) focused on managing the steering system production, where we aimed to increase driver confidence in the car while also improving serviceability. 2016 was a significant year for the team because it was our first year to complete a car that could pass technical inspection and drive at competition, which yielded a 6th place overall finish.

Design Focus

The steering system dictates the size of the car’s turning radius, the dynamics of how the steering wheel affects the angle of the tires, and the effort required by the driver to turn the car. Benchmarking off of the team’s 2015 car (not pictured), the system targets for MY16 (pictured) focused on improving significant backlash and serviceability issues that had plagued the previous year’s car.

The team’s previous two vehicles featured steering systems secured with bolts in shear, causing significant backlash- a phenomenon where you can turn the steering wheel significantly without the slightest tire movement. This in itself made our drivers uncertain when traversing any course, causing them to over-slow the car simply due to the uncertainty of how much they could turn the car. Without fixing this, it wouldn’t matter how well the rest of the car was designed because the driver wouldn’t be able to comfortably use the system to its greatest capacity.

Design Realization

We minimized backlash via splined joint connections to increase steering response and precision. With each shaft’s rotation being efficiently transferred to the full system, driver comfort improved because turning inputs resulted in consistent outputs. The results were particularly noticeable with novice drivers in the seat.

With two new team members helping, we completed a system that improved serviceability, decreased weight, and improved steering precision, meeting our goals for the year. A removable shaft mount (showed in the rightmost picture above) allowed for easy system installation and maintenance because the middle U-joint was not constrained by two rigid mounts until secured by the 2nd mount’s bolts. Despite adding complexity to the mounting structure and requiring larger U-joints for splines, we reduced the steering system’s mass by 7% over MY15 and reached design finals at the competition with the full-car design.

Fast facts

• - We used a Kaz Technologies splined steering rack designed for FSAE cars. You can find information on it on their website, here.

• - The steering rack is heavier than some options, but a key criteria for us was making sure the driver felt confident when in control of the vehicle inputs. While more qualitative than quantitative, it was still a key metric because the target user is a student driver who usually has minimal experience driving at a vehicle’s traction limit; ease of use is crucial to enabling the driver to maximize the car’s performance.

• - If you’re designing your own FSAE steering rack or considering different options, splined shafts are the gold standard. A lighter system will not be worth it unless the backlash in the system is controlled.

• - After the rack decision, the next most important piece to the design is the Ackerman angles, rack travel ratio, and steering linkage geometry; however, those were not the focus of the improvements for this design cycle, so will not be discussed on this page.