Gecko climbing robots
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Mechanical engineering description of the gecko-like climbing mechanism; biomechanics explanation of the actual gecko feet biological mechanisms
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Gecko climbing robots
- 1. BME500 Biomechanics and Biorobotics Rano Sidhu & Raul Soto http://roboticsnedir.com/2010/08/27/gecko-robot-gives- spiderman-some-tough-competition/
- 2. Mobile robots able to climb and maneuver on vertical surfaces are useful for inspection, surveillance, and disaster relief applications Kim (2008)
- 3. http://media.treehugger.com/assets/images/2011/10/gecko-foot.jpg http://www.sciencephoto.com/media/344470/enlarge Stickybot III Gecko • High sticking power • Easy to peel off
- 5. Four legs, Each with four degrees of freedom Actuation at the wrist to expand beyond vertical- only climbing of the first platform. At the body level, Stickybot has 12 servomotors 32 degrees of freedom (DOFs), making it highly underactuated.
- 6. Each motor has a local microprocessor-based servo controller. The feet are detachable. Stickybot III can currently climb at 5 cm/sec. The robot has a snout-vent length of 36 cm, and the tail adds an additional 40 cm. The smoother the surface is, the easier Stickybot III can climb it
- 7. The robot has rotatable ankles. When a gecko goes down a wall upside-down, it will reverse its back feet such that they point upward. All computation is done on the robot using a 40 MHz PIC microcontroller. A computer can send commands such as 'start' and 'stop' over a Bluetooth connection, but the robot does not require an external computer or sensors.
- 8. Bar mechanism to keep the stroke and elbow servos close to the body. The red joints are active; green joints are passive. The ankle motor is intended to keep the feet aligned so that tangential forces are in the correct direction for the directional adhesives. Rotates in and out of the plane of the screen using another "wing angle" servo motor http://bdml.stanford.edu/pmwiki
- 9. The wing moves the foot towards or away from the wall. The wing servo rotates a carriage that holds the stroke and elbow servos.
- 10. Helps reduce the pitch-back torque on the robot. The lowest point on the robot presses into the window since the center-of- mass is a significant distance from the wall. Using a tail means the back feet can act as adhesives. Without a tail, only the front feet would be adhering to the window in tension and the back feet would be in compression.
- 11. The tail and body are held together using strong magnets. This allows the tail to break- away during a fall, but also detach for storage as well as for demonstrations on the utility of the tail. The tail's hinge has a thumb-screw to adjust the angle and interchangeable springs to adjust the stiffness.
- 13. Four segmented toes molded with two grades of polyurethane that sandwich a thin polyester fabric The fabric flexes easily, but is relatively inextensible Transmits shear stresses across the surface of the foot Avoids the buildup of stress concentrations Peeling, at the proximal regions of the toes.Kim, S. et al. 2007
- 14. Conform to gently curved surfaces. Peel backward in a motion like hyperextension of geckos toes detachment. Servomotor connected via push–pull cables in sleeves, Attached to a rocker– bogie linkage located at the foot
- 15. Uniform stress distribution when the toes are deployed on a flat surface
- 16. Anisotropic hairs comprised of Shore-A polyurethane. Hairs measure 380 μm in diameter at the base. The base angle is 20◦ and the tip angle is 45◦.
- 18. 1 2 3 4 Not in contact with the wall In contact with the wall • Legs 1 and 4 make contact with the wall. •Weight is transferred from one pair to the other. • Legs 2 and 3 release from the wall.
- 19. 5 highly flexible digits Each has toe pads with hundreds of thousands of setae Each seta has a stalk of hundreds of 200 nm – wide spatular tips Adhesion via Van DerWaals forces! Autumn (2006)
- 21. 6 mechanical properties Useful for attaching / detaching in energy-efficient manner Cantilever Effect Lever Effect Footprint Effect Peeling Effect Stiffness Asymmetry Momentum Distribution Autumn (2006)
- 22. Cantilever-shaped hairs enable robust grip on irregular surfaces Berenguer(2007)
- 23. Lever principle : the longer the hair, the lesser the force needed Detachment occurs in path of least effort First rotation of hair, then peeling MR > Madh : moment due to external force applied to hair > moment over rotation axis due to adhesion force Berenguer (2007)
- 24. ML : maximum load a hair can support MR and ML depend on shape of footprint Different footprint shapes = different MR / ML ratios High MR / ML ratio : support higher load, lower release force needed Triangle-shaped footprint has higher MR / ML ratio, for a constant area, length, adhesion pressure Berenguer (2007)
- 25. When load acts on lower extreme of setae, hairs detach one by one in a coordinated way The more contact points => more efficient adhesion system Peak detachment force and maximum load capacity are proportional to the number of contact points Berenguer (2007)
- 26. Due to curvature of the hairs Stiffer hairs are easier to detach from non-flat surface (+/-) Δx: decrease/increase distance d between load cell and stage (+/-) y: hair in tension / compression When hair changes from tension to compression, its stiffness increases by almost 3x kT = 1.5 g/m => kC = 4 g/m Berenguer (2007)
- 27. Ability to distribute a big load into smaller loads to each hair Curved shape of gecko hairs distribute loads and tensions homogeneously If forces and tensions are not distributed homogeneously, some hairs will detach => peeling crack will propagate => loss of adhesion in whole foot
- 29. Autumn, K. et al. 2006. Effective Elastic Modulus of Isolated Gecko Setal Arrays. Journal of Experimental Biology. 209:3558-3568. Autumn, K. et al. 2006. Frictional Adhesion: A New Angle on Gecko Attachment. Journal of Experimental Biology. 209:3569-3579. Berengueres, J. et al. 2007. Structural Properties of a Scales Gecko Foot-Hair. Bioinsp. Biomim. 2:1-8. Kim, S. et al. 2007. Whole Body Adhesion: Hierarchival, directional and distributed control of adhesive forces for a climbing robot. 2007 IEEE International Conference on Robotics and Automation. 10-14 April 2007. Kim, S. et al. 2008. SmoothVertical Surface Climbing With Directional Adhesion. IEEE Transactions on Robotics. 24(1):65-74. http://bdml.stanford.edu/pmwiki