Situation

The wheel assembly was a critical part of the rover’s chassis and suspension system. In the previous design, the rover’s weight caused the mechanical connection between the motors and wheels to bend, reducing the reliability of the drivetrain.

To solve this structural issue, the team selected commercial scooter hub motors, which integrate the motor directly into the wheel and eliminate the need for a separate motor-to-wheel connection. However, the stock scooter tires were narrow and designed for smooth pavement. Their limited contact area and geometry did not provide sufficient traction or compliance for an all-terrain rover.

Before modification

After modification

Task

My task was to develop a wider all-terrain tire system that could be installed over the existing scooter tires. The new design needed to:

Prevent rotational slippage between the custom tire and the existing hub-motor tire.
Improve traction between the rover and uneven ground.
Support the rover’s weight while remaining sufficiently compliant.
Be easy to manufacture, assemble, remove, and iterate.
Preserve the commercial hub motor without requiring permanent modifications.

Action

I selected 3D-printed TPU as the material and manufacturing method because it allowed me to customize the tire geometry, tune its flexibility, and produce new prototypes quickly. Compared with a conventional rubber tire, a printed TPU tire gave me direct control over the contact width, structural stiffness, wall thickness, and internal density.

I completed eight rapid prototype iterations. As soon as each printed part became available, I tested its fit, assembly process, deformation, and traction, then immediately incorporated the results into the next CAD revision.

The first prototype focused on establishing the correct tolerance around the existing scooter tire. I then developed a two-piece proof-of-concept design that enclosed the original tire between two TPU sections. This configuration allowed the over-tire to be installed without disassembling the hub motor.

Later prototypes refined the interface and maintenance features. I introduced an interference fit to prevent relative rotation between the TPU over-tire and the original rubber tire. I also added chamfers to guide the parts into position during assembly, along with handling features and fastener holes that made installation and removal easier.

To balance load support with terrain compliance, I adjusted the printing parameters rather than treating the tire as a uniformly solid component. I tested wall counts between five and ten layers and used a graded internal structure: lower infill near the sides allowed the tire to deform around uneven surfaces, while higher density through the center provided greater support under the rover’s weight. This created a practical balance between stiffness, softness, and traction.

I also explored an alternative concept that removed the stock tire entirely and mounted the printed TPU structure directly to the hub-motor rim. This approach provided significantly more freedom for the tire’s geometry and internal structure. However, the hub motor was difficult to disassemble safely because of its strong internal magnets, so the over-tire configuration remained the more serviceable solution for the current rover.

Version 1

Version 2

Version 3

Result

The final TPU over-tire achieved a secure mechanical connection with the existing scooter tire. The interference-fit interface eliminated rotational slippage between the two tire layers, while the wider and more compliant geometry produced reliable traction between the rover and the ground.

The project also established a fast, repeatable development process for future wheel designs. By combining rapid TPU printing, immediate physical testing, and iterative CAD refinement, I transformed a narrow commercial scooter wheel into a serviceable all-terrain wheel system without modifying the hub motor itself.

All-Terrain TPU Over-Tire for a Rover