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GECKO-LIKE “STICKYBOT III”
BME500 Biomechanics and Biorobotics
Rano Sidhu & Raul Soto
http://roboticsnedir.com/2010/08/27/gecko-robot-gives-spiderman-some-tough-competition/
Purpose Mobile robots able to
climb and maneuver on vertical surfaces are useful for inspection, surveillance, and disaster relief applications
Kim (2008)
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
Stickybot III
http://bdml.stanford.edu/twiki/pub/Rise/StickyBot/FullMovie_V4_4small.mov
Stickybot III 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.
Sickybot III 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
Sickybot III 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.
Leg Mechanics 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
Servos The wing moves
the foot towards or away from the wall.
The wing servo rotates a carriage that holds the stroke and elbow servos.
Tail 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.
Tail 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.
Elements of hierarchical compliance
Toe Fabrication 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
Bent Toes 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
Cable Profiles Uniform stress
distribution when the toes are deployed on a flat surface
DIRECTIONAL FRICTION AND ADHESION
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◦.
DISTRIBUTED FORCE CONTROL
Weight Transfer During Trot
1 2
3 4
Not in contact with the wallIn 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.
Gecko Feet 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 Der Waals forces!
Autumn (2006)
http://www.youtube.com/watch?v=OoYeIsSkafI
http://www.psmicrographs.co.uk/gecko-foot/science-image/80016951http://robotics.eecs.berkeley.edu/~ronf/Gecko/interface08.html
http://www.psmicrographs.co.uk/_assets/uploads/moorish-gecko-foot-hairs--tarentola-mauritanica--80016981-l.jpg
How Gecko Feet Attach to Surfaces 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)
Cantilever Effect Cantilever-shaped hairs enable robust grip on
irregular surfaces
Berenguer (2007)
Lever Effect 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)
Footprint Effect 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)
Peeling Effect 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)
Stiffness Asymmetry Effect 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)
Moment Distribution Effect 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
Robot Adhesion Mechanisms
References 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. Smooth Vertical Surface Climbing With Directional Adhesion. IEEE Transactions on Robotics. 24(1):65-74.
http://bdml.stanford.edu/pmwiki