A Review of Active Mechanical Driving Principles of Spherical Robots <s> Notable Enhancements <s> This paper proposes a novel mechanical design of a three-legged reconfigurable robot. In its dormant form, the robot is packed into a spherical shape for minimum storage volume. At deployment, the robot can be transformed into a mobile form of two interconnected hemispheres with three legs, each equipped with an omni-directional wheel. Feasibility of the transformation process was analyzed using a dynamic simulation in MSC.ADAMS. The construction of the robot has been completed up to the deployment of three legs, the lifting of the robot body, and the movement of omni-directional wheels. The deployment of robot legs is controlled using feedback control on five dsPIC30F2010 boards. The torque measurements of the transformation process are in good agreement with the results of corresponding dynamic simulation. <s> BIB001 </s> A Review of Active Mechanical Driving Principles of Spherical Robots <s> Notable Enhancements <s> This paper presents a reconfigurable spherical robot. The reconfigurable spherical robot can be reconfigured into a form of two interconnected hemispheres with three legs equipped with three omni-directional wheels. A stable reconfiguration control algorithm is constructed to change the robot from spherical shape to two halves of interconnected hemispheres and three legged-wheeled expansions. This work also constructs a transformation controller for the robot which uses an accelerometer to sense its orientation. The performance analysis shows that our reconfigurable robot prototype can transform from spherical shape (dormant mode) into two interconnected hemispheres where the three leg-wheels are projected out of the shells (transformed mode) and vice versa. After the transformation into the three leg-wheel configuration, the robot can autonomously move in L-shaped and U-shaped areas as well as narrowing pathways. <s> BIB002
Novel add-ons to spherical robots are as diverse as the methods used to drive them. Designs incorporate sensors, telescopic cameras, reconfigurable legs, and even jumping mechanisms. Some designs even have the ability to transform completely. N. Chadill presents a reconfigurable robot that can transform from a sphere into a dual hemisphere platform with three legs and omnidirentional wheels BIB002 (Figure 11 ). The ideology behind the vehicle is that it can compact itself into a sphere for transportation and deployment but will function as a leg-wheeled robot after reconfiguration. The once spherical robot can then navigate pathways autonomously as any other wheeled vehicle can. Currently, the design does not actively roll when in its spherical configuration, but this idea can be applied to current spherical robot designs. Figure 11 . Image of spherical robot after reconfiguration BIB001 . Another reconfigurable spherical robot with deployable legs is Kisbot I, the predecessor to Kisbot II, which is mentioned in Section 2.2.5. Kisbot I has two types of drive modes: a pendulum-driven mode and wheel-driven mode  . While the legs are retracted to the interior of the robot, the robot can maneuver as a pendulum model. In its wheeled mode, the legs extend, stabilizing the robot, and it can be driven like a wheeled vehicle. The legs can also be deployed for stopping and climbing, seen in Figure 12 . Each leg resides in an independent hemisphere that can rotate independently of the other semi-sphere. Because the hemispheres are independent, the legs may not necessarily need to be deployed on the same Cartesian plane. This allows for the possibility of the robot to stabilize itself in unusual terrains. Another way to allow a spherical robot to climb large obstacles would be to give it the ability to jump. In a paper presented by L. Bing, a spherical robot driven by dual pendulums is retrofitted with a mechanism that gives it the ability to jump  . The jumping mechanism on the robot allows it to jump at a desired angle and direction once it has reconfigured itself to do so as shown in Figure 13 . This is an extremely useful characteristic for robots of this nature because of their inability to climb steep slopes. In order to jump, the robot stores energy in a spring by extending it with a large mass attached to it. When the spring is released, the mass is accelerated upwards and collides with the top of the robot. Due to the laws of conservation of momentum, the entire robot continues upwards with the mass. 