During high school, I had been fascinated by the Light Speed documentary about the World Solar Challenge — a 3000km race powered exclusively by the sun across the Australian Outback. As such, when I started at UBC in 2023, I was instantly interested when I heard that we had a solar vehicle team of our own, UBC Solar. I was fortunate to join the vehicle dynamics subteam right in the middle of a design cycle, and got to spend my first year on the team designing and building this steering wheel!
At the time I undertook this project, progress on our third generation car, Brightside, had been going well, and the mechanical and electrical sides of the team had already begun to outline some of the new things that would be needed on the steering wheel for the Gen2/Gen3 transition. These goals, in tandem with the 2024 competition rules, led to the following constraints and objectives in my design:
The wheel must fit within the tight rollcage, and accordingly shall be significantly smaller than a consumer vehicle counterpart. Consideration to driver ergonomics must be given throughout the design process.
This design will accommodate a PCB with the following interfaces — labelled, accessible to the driver and ideally in positions not requiring the driver to look down:
Horn
Push to talk
Next screen DID button
Cruise toggle button
Cruise increment button
Cruise decrement button
L/R turn signal switch
Regen enable switch (do not populate)
The wheel must have a continuous outside perimeter as detailed by Reg. 10.7.4, be sufficiently strong to be able to withstand loads the driver may impose on it, and feature a quick-release mechanism for driver egress. "A circular shape is preferred, however the upper part above 2/3 and/or the lower part below 2/3 of the circumference of the steering wheel may be flat as depicted in the diagram."
Some additional things to try to improve upon from the previous Daybreak wheel (pictured below) was its poor PCB enclosure, awkwardly-placed spokes, and heavy weight.
This list of requirements shrunk the solution space to a good size — I had some freedom in the final design, without needing to explore every possible geometry. At the time, I came up with three distinct designs.
Concept A Concept B Concept C
After some structured decision making and stakeholder consultation, I ultimately decided that Concept B appeared to be the most promising, and I proceeded to the next stage of design using this concept as my starting point.
As I fleshed out this concept, I identified a couple key aspects of the design that could be nailed down before moving onto detailed design and prototyping.
The first decision made about the design of the steering wheel was the shape. In response to driver feedback, it was decided to move the structural spokes to the 12 & 6-o'clock positions. This provided a more comfortable grip for the driver, and allowed the design to conform to the desired positioning of additional switches on the reverse of the wheel.
The decision was also made to adopt a rounder wheel profile, rather than the sideways-D shape used on the Daybreak wheel. This change provided a more consistent feel when repositioning hands during steering.
With the new wheel requiring twice as many buttons and switches as Daybreak, I had to carefully consider where to place them so the driver could operate controls by feel. As the front face of the wheel would be too crowded if I were to place all the buttons there, I had to get creative. The solution I came up with was to move some of these controls to the back of the steering wheel — under where a driver's index fingers would rest. To maintain the "operate by feel" principle, these controls would need to be larger than a standard button yet still tactile, and I deemed that using momentary (ON)–OFF–(ON) rocker switch, acting as two buttons, was perfect for this application. The switch that was later specced was the CW Industries GRB258I01BB.
I think it to be a fool's errand to design something in CAD without having a plan for a component's material and manufacturing plan. As such, before opening SolidWorks, I determined that a combination of FDM 3D-printed PLA grips together with a 1/8" 6061 aluminum baseplate would be strong enough to pass regulation while still using an additive manufacturing process that didn't heavily restrict the ergonomic shape of the wheel. While carbon fiber and SLS 3D printing would be expected to produce a lighter, higher-quality component, the availability of FDM 3D printers and a waterjet cutter on campus were ultimately responsible for the direction I took.
Early on in this project it had been decided to use a spare quick-release from Daybreak. This decision was made in regards to limiting project scope and saving money. However, in retrospect, purchasing a quick release with an integrated electrical connection would have been preferred to avoid the need for a seperate electrical connector.
One of the major upgrades for the new car was the incorporation of regenerative braking (a first for the team). Initially, the plan had been to control this system from a "paddle-like" interface on the steering wheel. I explored potential ways to implement this — from load cells to spring-loaded potentiometers, but found that the small bounding box of the steering wheel severely limited paddle travel, which would make modulation of brake force difficult for drivers. Ultimately, the decision was made to rely on one-pedal-driving for regenerative braking — with the driver instead controlling brake force with their feet.
My primary focus for this project was on the mechanical side, and I was fortunate to work with a talented member on the electrical team who created the PCB schematic. We worked together to select components and layout the board. More information about that project can be found in this excellent article.
I started prototyping the exact size of the steering wheel using cardboard-aided-design. While rudimentary, I was able to get a feel for the rough dimensions that would be comfortable while providing enough leverage for the driver.
Later, a curve was swept along the outside of this profile, and was 3D printed in rough quality to give a 3-dimensional feel to this mock-up. This helped determine the best diameter and thickness for the final wheel. Finally, all the critical pieces were printed in rough quality to test tolerances before printing the final wheel at a higher quality.
Integration with other components was first tested within CAD, and then later in the physical car with the driver. Tight timelines limited my ability to conduct an iterative finite element analysis (FEA) optimization of the baseplate weight, so a conservative FoS was used instead. The steering wheel was tested for final functionality/integration along with the rest of the Brightside car before heading to the 2024 Formula Sun Grand Prix.
The final high-quality grips were produced on a team members' personal Bambu Lab X1C printer + AMS, with PLA filament. Heat set inserts were pressed in with a soldering iron.
I exported a DXF file from SolidWorks, undersized holes in AutoCAD LT, and then prepared machine code in OMAX MAKE. The baseplate was then cut on a waterjet on campus and holes reamed to size on a drill press.
A key requirement for the assembly was to not require any soldering of the PCB. This was complicated by the panel mount rocker switches, which are traditionally pushed into a panel. As such, a specific assembly/disassembly order had to be followed to support the "collar" of the switch without desoldering it from the PCB. Regulations also necessitated locking wire be installed, so space had to be left between quick release bolts.
Images in this assembly diagram feature an unpopulated PCB as a populated PCB was not available at the time.
While I was very satisfied with the product I was able to create, and it was certainly an improvement upon the previous steering wheel, there remain places where the next steering wheel could improve upon.
Weight: One major area for improvement is weight. The current steering wheel (+quick release) weighs 746 g, mostly due to the complete overkill 1/8" 6061 aluminum baseplate. In future being more conservative with material and running FEA to verify functionality would be preferred. Perhaps moving to composite materials would suit this application.
Quick Release: As discussed earlier, another component which could be improved on is the quick release. As previously mentioned, moving to a quick release with electrical connections would be a massive benefit, removing the loose connector wire from the cockpit. In addition, a "ring style" quick release would be a better interface for the driver and would speed up egress.
More Buttons As the electrical side of the car grows more complex, having more controls readily available on the steering wheel may be an asset (just look at an F1 steering wheel). Thus optimizing the button layout for an increased number of buttons may become important in future.
