Sticybot

Stickybot is a quadruped robot capable of climbing smooth surfaces, such as glass, acrylic and whiteboard using directional adhesive. The design is mostly inspired by morphologic study of the best climber, Gecko lizard. The robot is operated by 12 servo motors controlled by PIC controller with force sensors. Stickybot is the incarnation of biomimetic design constituents that I invented, including underactuated hierarchical system, cable driven actuation and passive compliance-based force control scheme. I initiated and designed this robot for testing of synthetic gecko dry adhesion April 2005. After an year's furious effort on foot design, push-pull cable actuation mechanism, Stickybot succeeded to climb glass surface reliably.

Adhesion system model (What is stickiness?) -- Many people ask about what kind of material the sticky pads made out of and there is a large spectrum of surface energy. Adhesion is depends more on geometry of structures than the type of material. In the beginning of RiSE (Robots in Scansorial Environment) project, winter of 2003, Professor Kim was wondering about the mechanism why sticky stuff stick on surfaces. What feature makes things sticky? His hypothesis was that the more compliant the structure of a system, the stickier it is. One approach drawn from this concept is very simple Adhesion system model that was made in Jan 2004.

Hierarchical compliance system -- As mentioned in adhesion model, surface conformation is essential in adhesion since Van der Waals force is very weak unless there is intimate contact between two surfaces. Van der Waals force is known to be very weak, although its usage is ubiquitous in our life. Most common example is conventional tape that uses very soft material for compliance. Vertical climbing on various surfaces requires more sophisticated system than single thin layer of soft polymer used in tape. In natural and artificial environment, roughness in many length scale is presented. Thus, in order to maximize the number of molecules in intimate contact between feet and wall surfaces, corresponding length scale compliance is needed. Gekco species also present hierarchical compliance in their body. Flexible body and leg can conform at the centimeter scale. Toes and soft skin are responsible for 1~2 millimeter scale. Within a millimeter scale, specialized hair structures are composed of lamellae, setae and nano scale spatulae covering up to nanometer scale. Stickybot inherits similar characteristic comprising 12 active actuator, 8 DOF serial and 4 passive compliant DOFs in leg and 16 segmented toes controlled via two stage differential cable driven system.

Directional adhesion -- The most extraordinary feature of Stickybot is Directional adhesive. Climbing robot are not It has Anisotropic structure featured controllable adhesion with directionality in adhesion force. The movie clip demonstrates directional adhesion compared to conventional double sided tape. Unlike conventional tape, it sticks on smooth surface with very small preload and is also able to detach with by reducing load. If it is loaded in desired direction, it creates maximum contact minimizing stress concentration along the contact area. if it is loaded in wrong direction, the adhesion force is very low.

Underactuated system -- An underactuated system is a system that has more number of degree of freedom than number of actuators. Additional degree of freedom usually controlled by either spring damper system or differential system. Although underactuated system is introduced in order to reduce number of actuators, in many cases, taking advantage of passive mechanical dynamics. A good practical example is car suspension system. Considering a car suspension system as a robot arm, you will find 2 DOF.