Directional adhesion
Video & pictures
About  Sangbae....






Stickybot is....

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.- Video of Stickybot

Stickybot on
 Wired Science (Jan 3rd 8PM PBS)
TIME MAGAZINE : BEST inventions 2006.
 KBS 9PM News 11/20/2006
 SBS 8PM News    1/4/2007                                      
 KBS New year's special program '費諺聖 戚醤奄 杯獣陥'
             1/1 10:00am~12:00pm

   Principles of adhesion
Adhesion system modeling
ierarchical compliance
         Directional adhesion

    Design of Robot
       Underactuated system
       Foot design 
         Body design
         Push-pull cable system

Adhesion system model (What is stickiness?)

Many people asked me about what kind of material the sticky pads made out of and there is a large spectrum of surface energy. As I learned more about molecular mechanics, however, it is getting more convincing to me that 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, I was wondering about the mechanism why sticky stuff stick on surfaces. What feature makes things sticky? My 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 I 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

 - Spring damper system

Foot design

What makes Stickybot unique is its extraordinary design of foot. Its foot has four segmented toes controlled by single push-pull cable via two stage differential system. Three different polymers are used and stiffened by fine fabric to minimize shear stress concentration along adhesive pads. It took me about three month to finalize design iterating more than three times. Utilizing high surface energy of poly-urethane, we can test various adhesive pads on Stickybot feet.




Its interesting curvature of cable path is designed carefully in order to achieve well distributed normal force on the contact area. Since each toes has seven segments, it can conform non flat surfaces. Despite its flexible structure, reliable adhesion requires elaborated  force transmission system from cable tension to normal pressure on contact surface. Its desired profile is calculated in such a way shown on the diagram on right.

Basic idea is to create uniform normal pressure that caused by cable angle differentiation. Each segment should have same amount of force assuming constant cable compression force.





Differential cable system is employed in order of minimizing
number of actuators and force balance among four toes. One equivalent mechanical system is double rocker bogie system.Upper stage differential actuation is rocker and one cable connecting two toes enables lower stage differential system.



 Leg design with force sensor