Planetary Rover Wheel and Lower Leg Structural Design to Reduce Rock Entanglements

Abstract: This thesis looks at the SherpaTT planetary rover. The rover is a hybrid walking and driving rover that has been developed and built by DFKI and has already been deployed on several Mars analogue field studies. The SherpaTT rover wheels were found to become entangled in rocks during the last field deployment in Morocco. As human intervention would be impossible on Mars the aim is to reduce the possibility of rock entanglements by performing a mechanical redesign of the wheels. During this redesign care is taken to ensure the current traction, slip-resistance, weight and strength are not adversely affected. In addition, the durability of the wheels is investigated in terms of materials to review whether the current wheels are suitable for a mars deployment. An investigation into the grousers design results in a changed design that aims to both reduce rock entanglements and increase wheel performance by optimising the grouser height and number over several different wheel and terrain cases. Wheels are produced for four scenarios, a rigid wheel on hard ground, a rigid wheel on soft ground, a flexible wheel on hard ground and a flexible wheel on soft ground. A conceptual investigation into the wheel fork design is carried out to examine the effects of changing three properties of the wheel fork. The magnitude and location of the stress is compared for each. Materials are investigated resulting in the recommendation of several potential material choices which provide an increase in the overall strength and hardness. While SherpaTT is still in development the 6000 class of aluminium is recommended due to the relative ease with which it can be worked with. Once SherpaTT moves onto the final stages it is recommended that at least the grousers are made from the 7000 class of aluminium, which have higher levels of strength and hardness.