High-Performance Wheel System
Owned every generation of Hydron’s wheel system, including sub 1-gram PEEK wheels for our world finals campaign.
The system
The wheel system covers the car-side axle and hub, the wheel itself, and the bearing interface between them. I designed all of it, optimising a lightweight, low-inertia, yet highly rigid PEEK wheel running on a press-fit bearing.
Hydron Proton M10 wheel system (purple) and wheels
The core trade-off
A fast wheel is constrained in three directions. Low rotational inertia wants material removed as far from the axle as possible, so the wheel can spin up quickly off the launch. Stiffness wants material kept; the car is violently knocked and pitched at launch; wheels can lift off the track and slam back down, and a wheel that deflects bleeds energy and speed. Low rolling resistance depends on that same stiffness. Designing the wheel was about balancing those demands with the right selection of materials, processes, and geometry.
The case for stiff wheels on an F1 in Schools car can be best seen in one of my track testing campaigns in earlier years, in which I ran a range of prototype wheels on a dedicated prototype car with visual tracking markers. A plot of the rear tracking sticker position showed noticeable peaks in the vertical axis, most visible in the lightest and most elastic wheel set, which is best attributed to a bouncing instability.
The case for stiff wheels: Hydron track test car (left) and point tracking (right)
My final design for the world finals was a 5-spoke PEEK machined wheel running on a thru axle mounted on SLS printed Nylon 12 support systems on the car body side. This gave the best balance between the design requirements and was of a manufacturable design in which I coordinated with a local shop to machine. The selection-optimised bearing was held in with a press-fit to maintain concentricity and avoid the use of glue (which is a very bad idea around bearings this small).
Final wheel simulation (left) and as-manufactured (right)
Five generations, including a calculated risk
I developed every iteration of our wheel system, five in total that were used in competitions. At the 2020 State Finals I took a calculated gamble to use that competition as a testing ground and introduced a new wheel system. Lockdowns that year meant we had limited time and resources to run a detailed testing campaign, while the state finals had become a generally safe competition for us (we were confident in our other project areas being able to lift our scores up sufficiently to guarantee a spot at the national finals, should the wheel system fail). As such, I fitted a double-bearing wheel concept to the rear wheels (while the front had an old proven design to contain risk). The premise was simple: rotate the inside races of the bearings instead of the outside to cut ball bearing rolling distance (and a linear model of friction) by a third; two bearings were required to maintain alignment of the axle. This process earned me an ADF Future Innovators Awards.
2020 Victorian State Final car exploded view showing different front and rear wheel systems
Ultimately, bearing alignment issues meant the wheel system underperformed. I still believe the experiment was valid as it was an issue that could only be discovered through physical manufacture and testing; further, one of the fastest teams at the world finals managed to make a double bearing system work which validates some of my initial assumptions.