Design and Analysis of a Mechanical Hopping Mechanism Suited for Exploring Low-gravity Environments

Exploration of extreme environments, including caves, canyons and cliffs on low-gravity surfaces such as the Moon, Mars and asteroid surfaces can provide insight into the geological history of the solar system, origins of life, and prospects for future habitation and resource exploitation. Although current methods of exploration utilizing wheeled ground rovers have excellent performance on relatively flat, benign, even terrains, they are unsuitable for exploring these extreme environments due to their inability to travers rugged environments as their obstacle traversing capabilities are typically limited to wheel diameter, and reduced traction on low-gravity environments. So, developing small, cost-effective robots that can utilize unconventional mode of mobility through ballistic hopping can overcome these limitations. Our past work has proposed using a spherical robot (SphereX) that achieves ballistic hopping mobility through the use of a miniaturized propulsion system and 3-axis reaction wheel system. In this paper, we present the design and control analysis of a mechanical hopping mechanism that can be used for SphereX. The mechanism is comprised of two mechanical systems to produce its ability to maneuver terrain and achieve mobility through ballistic hopping. On the robot's interior, it consists of an electric gearmotor attached to a set of gears, a spring, and a rubber foot. These components make up the hopping mechanism used to hop the robot by applying a force along the longitudinal axis of the spring between the rubber foot and the ground. However, the robot needs to be oriented in a desired orientation in order to achieve ballistic hopping and intercept a desired target. This is achieved through a secondary mechanical system that consists of three linear actuators each connected to levers which are mounted to the exterior of the robot's shell. The lever and the linear actuator system are used to orient the robot in a desired orientation so that when the hopping mechanism is deployed it will be launched in a ballistic trajectory to intercept a desired target. Although the spring based hopping mechanism provides a constant force, but the lever and linear actuator-based system is used to orient the robot at different angles to produce range in mobility. The robot also consists of electronics and sensors equivalent to current smartphones, an array of guidance, navigation and control sensors, lithium-ion battery-based power system and a volume for science payload.