We also decided to develop a new wheel for our rover. Our first model was based on a future Mars rover wheel, new wheels were being developed due to the wheels on the curiosity rover being damaged. Designing the CAD model showed the complexity of the design when minimised. The chain-link of the tire proved the most challenging due to not having the shape memory alloy, however, NASA developing 3D printable chain mail was an idea to replace the tire. 

Due to the shape memory alloy tyre being too complex, we decided to research other tyres. Further research showed 3D printable airless tires, these seemed to be more time-efficient to design and manufacture. Therefore, multiple models were designed to determine the correct set of arches. 

We 3D printed the wheels using Thermoplastic Polyurethane (TPU), to determine the best model to use for our rover. TPU was used due to it being able to create 3D flexible models. The test determined that 13 arches would be perfect for our rover, the first model deformed too much and the third model didn't deform.

To simplify the design of JPL's open-source mars rover a different suspension system was designed. The legs would be designed using a metal pipe, and they would be connected using a joint that would be manufactured using sheet metal. Design 2 was a proof of concept, this design allowed us to see errors that would be in manufacturing our rover. Such as forming legs from welding metal pipes and buying ball joints that meet our requirements.

Our next design changed the legs of the rover to be manufactured by using 3D printing, The rectangular area of the leg added to the ease of manufacturing. We also designed custom ball joints, this solved our issue of having to design our rocker-bogie system around pre-made ball joints. The problems with this design were not being able to add a ball bearing to smooth the motion on the rover, excess weight and difficulty to manufacture ball joints.

We first printed the ball joints, which led to us noticing there were issues with: 

• Elephant foot

• Tolerances

• Layer Lines

To fix our issue with elephant foot, we added chamfers on the bottom of the ball joint which allows the part to not be fused together.  Our next issue was the tolerances on the ball joint, early models had very loose ball joints which led to them falling off. To stop this the tolerances were changed and the top was extruded. to stop the ball from falling off. Our final issue was creating rods to join the ball joint, due to how they were printed, they are weak along the layer lines which led to them snapping very easily. A new model was designed that accounted for all of these issues, which allowed us to continue to print our larger parts.

Once assembled, we tested the suspension system by creating our own obstacle course matching the specification of the design brief. We first used a laptop with dimensions of Dimensions (H x W x D) 321.5mm x 217.5mm x 17.9-20.8m, the depth matched the specification needed for our rover.