MECHANICAL SPIDER- GQ64
1. INTRODUCTIONGQ64 is not a robotics based machine. It is the
simplest form of mechanism which runs with the help of mechanisms
like Gear drive Belt drive Muter drive Chain and sprocket drive
Walking mechanism has been for long a dynamic and fast developing
field of mechatronics. This huge interest not only derives from the
obvious fact that the usage of legs resembles the way of movement
of living animals, but also to its great advantage while moving on
a rough, unstructured surface. Due to the possibility to stand on
single, well defined points a flexible operation area is
achieved.As a drawback, efficiency and speed are not the strongest
qualities of walking mechanism. When it comes to flat, even
terrain, moving with wheels turns out to be the faster, more
reliable way of locomotion.The invention provides a walking device
which stimulates a gait of a legged animal. The device includes a
frame with spaced axial mounts, a leg, axially connected upper and
lower rocker arms which limit reciprocating leg motion. The leg is
driven by a connecting arm powered by a rotating crank. The
position and configuration of the axialconnecting sites establish a
prescribed orbital path that the foot undertakes with each
revolution of the crank. Both rocker arms and the crank are axially
mounted to the frame. The leg has a hip joint axially connected to
the upper rocker arm for limiting hip motion, a foot and a knee
joint axially connected to the connecting arm. The connecting arm
has three axial connecting sites, one for connecting to the knee,
another to the crank, and a third connecting site defined as a
centrally disposed elbow joint connecting site which connects onto
the lower rocker arm and limits knee joint motion. Under power,
crank rotation is transferred to the connecting arm causing the leg
to move in an accurate reciprocating movement of a restricted
actual pathway which stimulates the gait of the legged animal. The
walking device may be manually powered or motorized by applying
motorized power to the crank axles.
1.1WHAT IS GQ64? G - General Q - Quadric System6 - Six Links 4 -
Four Legs
Fig. 1 Mechanical Spider 1.2 MECHANISMS USED 1.2.1 Klenn
mechanistic mechanismKlenn mechanism is a planar mechanism designed
to simulate the giant legged animal and function as a wheel
replacement. Here we are using a single leg consists of a six bar
linkage made up entirely of pivot joint that converts rotating
motion into linear motion. The linkage consists of the frame, a
crank, two grounded rockers, and two couplers all connected by
pivot joints. The proportions of each of the links in the mechanism
are defined to optimize the linearity of the foot for one-half of
the rotation of the crank.The remaining rotation of the crank
allows the foot to be raised to a predetermined height before
returning to the starting position and repeating the cycle. Two of
these linkages coupled together at the crank and one-half cycle out
of phase with each other will allow the frame of a vehicle to
travel parallel to the ground. The Klenn linkage provides many of
the benefits of more advanced walking vehicles without some of
their limitations. It can step over curbs, climb stairs, or travel
into an area that are currently not accessible with wheels but does
not require microprocessor control or multitudes.
Fig. 2 Klenn mechanistic mechanism chain
1.2.2 Anatomy of SpiderMost insects have three body parts.
Spiders and other arachnids have only two major body parts. The
anterior part is called the cephalothoraxesOr prosoma and the
posterior part are called abdomen, or opisthosoma.Spiders have
eight legs attached to the cephalothoraxes and each pair of legs is
numbered I, II, III and IV from anterior to posterior. Each leg is
composed out of seven segments: coxa or basal segment, the
trochanter, femur, patella, tibia, metatarsus and tarsus.In some
spider families the tarsus ends in two claws, in others it ends in
three claws, depending on the adaptation to the environment and
hunting technique.The front appendages are called pedipalps and
have only six segments: coxa, trochanter, femur, patella, tibia and
tarsus. Different types of hairs (setae) and spines (macro setae)
are present on the legs. Also, long hairs are present called
trichobothria and these hairs are used as sensory units and they
originate in sockets with multiple nerve endings. These hairs are
extremely sensitive to air currents and to vibrations, compensating
for the extremely poor eye sight of some spiders thus helping them
hunt. Different types of hairs and bristles are found on the legs,
depending on the different taxa, as adaptation to the environment
and climbing or hunting techniques. For example, the spiders in the
family Theridiidae are called comb-footed spiders because of the
appearance of the bristles that they have on the ventral side of
the tarsus.
Spider LegsIn order to be able to climb various surfaces the
spiders use two types of different attaching mechanisms: the claws
and the hairs.As regards as the claws such a mechanisms are used
for two major operations: Locomotion, used during climbing rough
hard surfaces (stone) or soft surfaces (tree bark, leaves) Web
building, used to spin the silk threads or walk on the already
built web.Web building spiders have three claws and use the claw in
the middle to grasp the silk threads.Jumping spiders and generally
spiders that do not use webs to capture the prey do not need
specialized claws to spin the silk threads.
1.3 TRANSMITTING SYSTEMWhich type of system you need to provide
the power into legs for translation motion , in this system crank
are the most common part because the main power are transmitted in
crank , crank rotates with his own center the leg are joint with
the help of pivot .
1.3.1 Main type of transmitting 1. Mechanical spider with gear
mechanism2. Mechanical spider without gear
1.3.2 MotivationTo overcome the previously mentioned problematic
a practical solution would be to enable different ways of
travelling for one robot, rolling and walking, to adapt it to a
changing environment in an easy way. In this bachelor thesis this
task is realized by implementing feet equipped with passive skates
on a walking robot, deriving a skating trajectory and does first
steps into optimization of this movement. One of the main reasons
for this choice was that the robot stays in the environment it is
geared to. Therefore not the whole robot, but only the feet had to
be altered.
1. BASIC STUDY ABOUT MECHANISM2.1 Planar and Spatial
MechanismsMechanisms can be divided into planar mechanisms and
spatial mechanisms, according to the relative motion of the rigid
bodies. In planar mechanisms, all of the relative motions of the
rigid bodies are in one plane or in parallel planes. If there is
any relative motion that is not in the same plane or in parallel
planes, the mechanism is called the spatial mechanism. In other
words, planar mechanismsare essentially two dimensional while
spatial mechanisms are three dimensional. When one of the links of
a kinematic chain is fixed, the chain is known as mechanism. It may
be used for transmitting or transforming motion e.g. engine
indicators, typewriter etc,A mechanism with four links is known as
simple mechanism, and the mechanism with more than four links is
known as compound mechanism. When a mechanism is required to
transmit power or to do some particular type of work, it then
becomes a machine. In such cases, the various links or elements
have to be designed to withstand the forces (both static and
kinetic) safely.A little consideration will show that a mechanism
may be regarded as a machine in which each part is reduced to the
simplest form to transmit the required motion.1.1.1 NUMBER OF
DEGREES OF FREEDOM FOR PLANAR MECHANISMIn the design or analysis of
a mechanism, one of the most important concerns is the number of
degrees of freedom (also called movability) of the mechanism. It is
defined as the number of input parameters (usually pair variables)
which must be independently controlled in order to bring the
mechanism into a useful engineering purpose. It is possible to
determine the number of degrees of freedom of a mechanism directly
from the number of links and the number and types of joints which
includes.
Fig. 3 Mechanisms Schismatic Diagram of Mechanical Spider
Now let us consider a plane mechanism with l number of links.
Since in a mechanism, one of the links is to be fixed, therefore
the numberOf movable links will be (l 1) and thus the total number
of degrees ofFreedom will be 3 (l 1) before they are connected to
any other link. InGeneral, a mechanism with l number of links
connected by j number of Binary joints or lower pairs (i.e. single
degree of freedom pairs) and h Number of higher pairs (i.e. two
degree of freedom pairs), then theNumber of degrees of freedom of a
mechanism is given by- n = 3 (l 1) 2 j hKutzbach Criterion to Plane
Mechanisms n = 3 (l 1) 2 j hGrublers Criterion for Plane
MechanismsThe Grublers criterion applies to mechanisms with only
single degree of freedom joints.Where the overall movability of the
mechanism is unity. Substituting n = 1 and h = 0 in Kutzbach
equation, we have;1 = 3 (l 1) 2 j, Or 3l 2j 4 = 0This equation is
known as the Grubler's criterion for plane mechanisms with
constrained motion. A little consideration will show that a plane
mechanism with a movability of 1 and only single degree of freedom
joints cannot have odd number of links. The simplest possible
machanisms.of this type are a four bar mechanism and a slider-crank
mechanism in which l = 4 and j = 3.2Kinematics and Dynamics of
Mechanisms.
2.2 KINEMATICS, KINETICS, DYNAMICS
Kinematicsof mechanisms is concerned with the motion of the
parts without considering how the influencing factors (force and
mass) affect the motion. Therefore, kinematics deals with the
fundamental concepts of space and time and the quantities velocity
and acceleration derived there from.Kineticsdeals with action of
forces on bodies. This is where the effects of gravity come into
play.Dynamicsis the combination ofkinematicsandkinetics. Dynamicsof
mechanisms concerns the forces that act on the parts -- both
balanced and unbalanced forces, taking into account the masses and
accelerations of the parts as well as the external forces.
2.3 LINKS, FRAMES AND KINEMATICS CHAIN
Alinkis defined as a rigid body having two or more pairing
elements which connect it to other bodies for the purpose of
transmitting force or motion in every machine, at least one link
either occupies a fixed position relative to the earth or carries
the machine as a whole along with it during motion. This link is
theframeof the machine and is called thefixed link.Each part of a
machine, which moves relative to some other part, is known as a
kinematic link (or simply link) or element. A link may consist of
several parts, which are rigidly fastened together, so that they do
not move relative to one another. For example, in a reciprocating
steam engine, piston, piston rod and crosshead constitute one link
; connecting rod with big and small end bearings constitute a
second link ; crank, crank shaft and flywheel a third link and the
cylinder, engine frame and main bearings a fourth link.A link or
element needs not to be a rigid body, but it must be a resistant
body. A body is said to be a resistant body if it is capable of
transmitting The required forces with negligible deformation. Thus
a link should have the following two characteristics:1. It should
have relative motion, and2. It must be a resistant body
2.3.1 Types of LinksPiston and piston rod of an IC engine. In
order to transmit motion, the driver and the follower may be
connected by the following three types of links:1. Rigid link. A
rigid link is one which does not undergo any deformation while
transmitting motion. Strictly speaking, rigid links do not exist.
However, as the deformation of a connecting rod, crank etc. of a
reciprocating steam engine is not appreciable; they can be
considered as rigid links.2. Flexible link. A flexible link is one
which is partly deformed in a manner not to affect the transmission
of motion. For example, belts, ropes, chains and wires are flexible
links and transmit tensile forces only.3. Fluid link.A fluid link
is one which is formed by having a fluid in a receptacle and the
motion is transmitted through the fluid by pressure or compression
only, as in the case of hydraulic presses, jacks and brakes.
2.4 KINEMATIC PAIRThe two links or elements of a machine, when
in contact with each other, are said to form a pair. If the
relative motion between them is completely or successfully
constrained (i.e. in a definite direction), the pair is known as
kinematic pair. First of all, let us discuss the various types of
constrained motions.
2.4.1 Types of Constrained MotionsFollowing are the three types
of constrained motions:1. Completely constrained motion. When the
motion between a pair is limited to a definite direction
irrespective of the direction of force applied, then the motion is
said to be a completely constrained motion. For example, the piston
and cylinder (in a steam engine) form a pair and the motion of the
piston is limited to a definite direction (i.e. it will only
reciprocate) relative to the cylinder irrespective of the direction
of motion of the crank.
2. Incompletely constrained motionWhen the motion between a pair
can take place in more than one direction, then the motion is
called an incompletely constrained motion. The change in the
direction of impressed force may alter the direction of relative
motion between the pair. A circular bar or shaft in a circular
hole, as shown in Fig. 5.4, is an example of an incompletely
constrained motion as it may either rotate or slide in a hole.
These both motions have no relationship with the other.
3. Successfully constrained motion When the motion between the
elements, forming a pair, is such that the constrained motion is
not completed by itself, but by some other means, then the motion
is said to be successfully constrained motion. Consider a shaft I
.The shaft may rotate in a bearing or it may move upwards. This is
a case of incompletely con-strained motion. But if the load is
placed on the shaft to prevent axial upward movement of the shaft,
then the motion of the pair is said to be successfully constrained
motion.
2.4.2 Classification of Kinematic PairsThe kinematic pairs may
be classified according to the following considerations:1.
According to the type of relative motion between the elements. The
kinematic pairs according to type of relative motion between the
elements may be classified as discussed below:(a) Sliding pair.
When the two elements of a pair are connected in such a way that
one can only slide relative to the other, the pair is known as a
sliding pair. The piston and cylinder, cross-head and guides of a
reciprocating steam engine, ram and its guides in shaper, tail
stock on the lathe bed etc. are the examples of a sliding pair. A
little consideration will show that a sliding pair has a completely
constrained motion.(b) Turning pair. When the two elements of a
pair are connected in such a way that one can only turn or revolve
about a fixed axis of another link, the pair is known as turning
pair. A shaft with collars at both ends fitted into a circular
hole, the crankshaft in a journal bearing in an engine, lathe
spindle supported in head stock, cycle wheels turning over their
axles etc. are the examples of a turning pair. A turning pair also
has a completely constrained motion.(c) Rolling pair. When the two
elements of a pair are connected in such a way that one roll over
another fixed link, the pair is known as rolling pair. Ball and
roller bearings are examples of rolling pair.(d) Screw pair. When
the two elements of a pair are connected in such a way that one
element can turn about the other by screw threads, the pair is
known as screw pair. The lead screw of a lathe with nut, and bolt
with a nut are examples of a screw pair.(e) Spherical pair. When
the two elements of a pair are connected in such a way that one
element (with spherical shape) turns or swivels about the other
fixed element, the pair formed is called a spherical pair. The ball
and socket joint, attachment of a car mirror, pen stand etc., are
the examples of a spherical pair.
2. According to the type of contact between the elements. The
kinematic pairs according to the type of contact between the
Elements may be classified as discussed below:(a) Lower pair. When
the two elements of a pair have a surface contact when relative
motion takes place and the surface of one element slides over the
surface of the other, the pair formed is known as lower pair. It
will be seen that sliding pairs, turning pairs and screw pairs form
lower pairs.(b) Higher pair. When the two elements of a pair have a
line or point contact when relative motion takes place and the
motion between the two elements is partly turning and partly
sliding, then the pair is known as higher pair. Pair of friction
discs, toothed gearing, belt and rope drives, ball and roller
bearings and cam and follower is the examples of higher pairs.3.
According to the type of closure. The kinematic pairs according to
the type of closure between the Elements may be classified as
discussed below:(a) Self closed pair. When the two elements of a
pair are connected together mechanically in such a way that only
required kind of relative motion occurs, it is then known as self
closed pair. The lower pairs are self closed pair.(b) Force -
closed pair. When the two elements of a pair are not connected
mechanically but are kept in contact by the action of external
forces, the pair is said to be a force-closed pair. The cam and
follower is an example of force closed pair, as it is kept in
contact by the forces exerted by spring and gravity.
3. INVERSION OF MECHANISMSWe have already discussed that when
one of links is fixed in a kinematic chain, it is called a
mechanism. So we can obtain as many mechanisms as the number of
links in a kinematic chain by fixing, in turn, different links in a
kinematic chain. This method of obtaining different mechanisms
byFixing different links in a kinematic chain is known as inversion
of the mechanism.
1. Four bar chain or quadric cyclic chain, 2. Single slider
crank chain, and3. Double slider crank chain.
3.1 Concept DeterminationSeveral concepts for feet giving the
robot the opportunity to reach new environ-ments or studying new
locomotion concepts were in mind. After reconsidering the potential
of different approaches their number could be reduced to the
following promising options
Fig. 4 Motion of Leg
A single leg consists of a six-bar linkage made up entirely of
pivot joints that converts rotating motion into linear motion. One
hundred and eighty degrees of the input crank results in the
straight-line portion of the path traced by the foot. The result of
two of these linkages coupled together at the crank and one-half
cycle out of phase with each other is a device that can replace a
wheel and allow the frame of the vehicle to travel relatively
parallel to the ground. The remaining rotation of the input crank
allows the foot to be raised to a predetermined height before
returning to the starting position and repeating the cycle.
Fig. 5 Final Motion
These figures show a single linkage in the fully extended,
mid-stride, retracted, and lifted positions of the walking cycle.
These four figures show the crank (rightmost link in the first
figure on the left with the extended pin) in the 0, 90, 180, and
270 degree positions.3.2 SKATINGIn this concept the robot travels a
flat, unstructured surface by skating. Each leg should be equipped
with passive wheels on the feet. By moving the feet in specific way
thrust is induced. Designing the specialized feet and deriving a
possible trajectory are the emphases of this approach. The goal
would be to move faster on the floor than with legged
locomotion
3.2.1 Selected Method of Skating, why??? It was decided to
further pursuit this way of movement for a couple of reasons: First
of all with eight legs on the floor a very stable system is
attained. Furthermore, lifting the legs would lead to a dislocation
of the robots center of mass. That means dynamic calculations have
to be applied leading to a more complex problem. Aside from that,
feet equipped with skating rolls turned out to be quite heavy. When
lifted up, high torques in the joints would be generated. That way
the motors could be overloaded.
4. KLENN MECHANISTIC MECHANISMThis mechanism is based on simple
kinematic chain, and kinematic chain based on links joint and
pivots.The study of Biological systems and methods has long
intrigued Scientists and Engineers in their quest for a greater
understanding of the world. Biological systems have managed over
thousands of years to evolve many methods for completing tasks that
are naturally impossible for humans such as re-growing missing
limbs, breathing underwater and even flying. Although humans have
managed to mimic some of these abilities through the inventions of
submarines and airplanes, there are still many areas of engineering
that these biological marvels can be applied to. Biometics, the
study of Biological methods and systems and their implications
toward robotic systems and engineering problems, is the term
applied to this ancient art, and has gained prominence in recent
years for its novel solutions.
Fig. 6 Graphical Motion of Legs
4.1 MOTION- (pictorial representation)FIG. 7 Diagram of
MotionFig. 7 (a)
Fig. 7 (b)
Fig. 7 (c)
Fig. 7 (d)
Fig. 7 (e)
Fig. 7 (f)
Fig. 7 (g)
Fig. 7 (h)
The Klenn linkage provides many of the benefits of more advanced
walking vehicles without some of their limitations. It can step
over curbs, climb stairs, or travel into areas that are currently
not accessible with wheels but does not require microprocessor
control or multitudes of inefficient actuator mechanisms. It fits
into the technological void between these walking devices and
axel-driven wheels.
5. FINIAL MECHANISM
Fig. 8
Fig. 95.1 SYSTEM OVERVIEW
The basic function of the GQ64 o move in a coordinated manner.
Much like real spiders, the gq64uld be designed to facilitate
vertical motion. The most common solution to this requirement is
making the design both lightweight and by using an
adhesiveSubstance on the feet.
The important functional requirements are listed below: Fur
legs( KLENN MECHANISM ) Three degrees of freedom on each leg
Lightweight Coordinated Movement in forward direction Ability to
stick to surfaces
5.2 RANGE OF MOTION
The range of motion (ROM) describes all positions the foot can
be moved to. It is derived from length of the leg elements and
obtainable angles between the segments. Furthermore, it had to be
guaranteed that the wheels stay in contact to the ground at all
times. With the geometry of the skating device and a security
factor to avoid the wheel suspension touching the ground a minimal
radius of 110 mm and a maximal radius of 410 mm was determined. For
these values are independent from the chosen angle, the range of
motion emerges as an annular area with the shoulder as a center The
minimum and maximum angle are defined by the bulges of the body
panel and therefore diver from leg to leg. For the leg L2 and R2
which were chosen to carry out the skating movement, the angle
ranges from the minimum of 94 to the maximum of 46 degrees.
5.3 RESTRICTIVE FACTORSUntil now, attention was only paid to an
ideal case, which strongly simplifies the reality. Since the thesis
is based on a real robot, the restrictive factors of the system
itself and of its interaction with a test environment had to be
taken into account.
5.4 THE EQUILIBRIUM LINEThe equilibrium line describes the set
of all positions in which the orientation of the skate is parallel
to the driving direction. This is the case if the current angle has
the same value as the angle of the leg. These positions generate
one defined line going through the center of the Shoulder and the
standard position of the foot. The great importance of this line
can be explained by observing the behavior of a skate positioned
once exactly on the line and once on the left respective the right
of it with a constant velocity of the shoulder. Starting with the
first case: By placing the wheel on the equilibrium line, a stable
state is obtained. To maintain the velocity of the shoulder, the
skate can stay passively on this position. To avoid this deadlock
position, the skate has to be pushed artificially over the line.
This is only possible in x-direction, since the skate constraint
blocks the y-direction. If the skate is now placed on the left of
the equilibrium line, a given velocity in the shoulder requires a
relative movement in positive y-direction such the skate has to
move along the rolling direction. Respective, placed on the right
side, the skate has to carry out a motion in negative y-direction .
The movement in positive respective negative y-direction is
depending on the total angular deflection measured from the
equilibrium line, the so called deflection angle. The bigger the
absolute value of this parameter becomes, the stronger is the
tendency to move in y-direction. Based on the previous
considerations to accomplish a closed movement, the trajectory has
to be positioned around the equilibrium line. A possible solution
is a Circular shaped trajectory that has to be travelled clockwise
on the left side And anticlockwise on the right side of the
machine.
6 MECHANICAL DESIGN OF SKATES6.1 RequirementsFor the feet with
integrated skating wheels, the following characteristics are
required: First of all, the feet have to be compatible with the
plug connection of the robot. Second, a skating roll with high
friction has to be integrated. Furthermore, the rolling direction
has to be adjusted for each leg to have all rolls directed forward
in the standard position6.2 Results of the Sector ApproachFor
particular selection of the actuating variables blurred
trajectories could be determined.As it can be seen in the movement
of the skate stabilizes on the same area for different starting
positions of the skate. The main difference between the behaviors
of the skate for different starting positions is the duration till
the movement is leveled off at the stable area. This conclusion is
only valid as long as the starting point is close to the
equilibrium line, since for remote staring points the motion turns
out to be unstable.
7. APPLICATIONSPotential applications would include anything
that currently uses wheels. The possibilities are limited only by
the imagination. Proposed concepts such as the ones reported on
regarding remote media reporters or various military land drones
could be improved with this linkage.Further development could
result in a production version of a wheelchair that could handle
curbs, sand, gravel, and stairs. Making the world of someone
confined to a wheel chair a much bigger place.The military, law
enforcement, Explosive Ordinance Disposal units, and private
security firms could also benefit from applications of the
spiderlike. It would perform very well as a platform with the
ability to handle stairs and other obstacles to wheeled or tracked
vehicles. Unmanned operations could be used for reconnaissance,
patrolling, hazardous material handling, clearing minefields, or
secure an area without putting anyone at risk. There would be
further benefits if a portion of these tasks could be automated or
made more accurate through Global Positioning Systems, infrared
viewing, and audio and video recording. It could be programmed to
patrol a predefined perimeter at random intervals.
8. FURTHER POSSIBLE UPGRADATIONSThe spiderlike linkage is a
basic concept similar to a wheel made out of stone. Wheels today
are still round but improvements in materials,Construction, drive
train, braking, and suspension have increased their usefulness and
efficiency. They are used on a wide spectrum of things from small
toys to huge pieces of mining equipment. This linkage will evolve
in much the same way. Different uses will have different
requirements that will drive modifications and advancements. Some
of the obvious ones are listed here.
FootDesign
There will be a general-purpose foot designed for a variety of
terrain types that could handle sand, rocks, or pavement.
Specialized feet will be developed to target specific conditions
such as sidewalks, curbs, or stairs and for amphibious vehicles
that are expected to travel in wet marshy areas or extreme rock
climbing vehicles requiring more traction.
Suspension
There are several areas that could be utilized for adding
suspension. The foot, leg, shock absorbing links, or attachment
points to the frame are severalpossibilities.
Collapsible
The frame and legs for small and mid-sized applications would
benefit from a collapsible configuration to increase options for
storage and delivery to target. A parallel linkage between the
frame and each pair of legs similar to ATV suspensions could be
exaggerated to allow the legs to fold up against the body when
fully lifted.
Amphibious
The legs can function as oars enabling the vehicle to paddle in
the water. This could be a passive design such as fixed canards,
hinged flaps, or openings designed into the legs that would
minimize the drag during the forward stroke on the portions of the
leg that are not lifted above the waterline and take advantage of
the motion of the leg on the return stroke to propel the vehicle
forward. A midpoint on the foldable suspension mentioned above
would position the legs to optimize the movement of the legs when
rowing. A walking machine with the ability to climb over obstacles
and swim across rivers would eliminate many of the restrictions
ofconventionalvehicles.
LeadingEdge Spurs
Teeth on the front edge of the legs allow the spider to step
onto obstacles taller than its step height, the highest point of
the foot during a cycle. The downward motion of the leading leg
will lift the body of the device if the spurs remain engaged until
the paired leg contacts the obstacle and continues to increase the
overall center of gravity.
TrailingUndercarriageSpurs
A single large protrusion on the trailing edge of each leg, if
appropriately designed, would enable the vehicle to crawl over
obstacles that would otherwise limit it based on ground clearance.
The translation and rotation of the leg during the propelling
portion of the cycle can be transferred with thismodification.
SpringAssist The use of springs to counter balance the momentum
of the legs as they move throughout the cycle would have benefits.
The ideal configuration would use springs with the appropriate
stiffness to create a system at
resonanceforaspecifictargetspeed.BucklingLeg
Toys would benefit from a leg that would unsnap or provide
spring-loaded relief when stepped on or dropped. Larger vehicles
could be designed with shear pins or breaking points that would
minimize structural damage during collisions, jumps and falls.
HybridLegs
Additional degrees of freedom could be added to the device by
controlling the length of various links with actuators. The added
complexity could have benefits. It would allow for precision
placement of the foot, increased step height, and still allow high
speed traveling when the standard length is locked in.
Speed-LevelingDriveTrain
The variation in the speed of the foot for a constant rotational
speed of the crank is not desirable. A variable crank rotation that
could compensate for these differences as well as the mechanical
advantage needed when stepping onto obstacles would minimize the
stresses on the drive trains of larger vehicles.
9. CONCLUSIONSkating motion with passive wheels under sustaining
ground contact is discussed. The basic idea was to predefine a
velocity of the robot and to analyze the resulting motion the skate
is forced in. Since the wheels areModeled as perfect skates, the
possible movement is strongly restricted by the constraint for
perfect skates, which forbids movement in axial direction.
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