These locomotion modes achieve forward movement by using a repeating pattern
of motion. One cycle of this pattern is called a gait.
Simple Gaits
|
| Slinky(RDB) |
 |
The robot moves like the slinky
toy, head-over-heels. This is achieved in two steps:
| • | when two ends are in contact with the ground, shift weight from
the rear foot to the front foot.
| | • | bring the rear foot over top and to the front, while maintaining
static stability. |
For the second step, static stability is maintained by ensuring the
vertical projection of the center of gravity of the robot remains in the
footprint of the foot in contact with the ground by the use of force
sensors in that foot.
A similar gait using the same principles is the cart wheeling gait.
It uses four legs instead of two and is shown in this small MPEG
simulation of cart wheeling ~230k
|
| 3Segment Slinky (RDB) |
 |
Similar to the Slinky, above,
however it is not completely statically stable, it uses its falling
inertia as part of the gait. The main significance of this gait is that
it uses the smallest number of segments that I could find for a simple
gait. Quicktime video of 3 segment
slinky ~1.8M . (this quicktime movie uses
Sorenson compression, which may not work with older plug-ins)
|
| Earthworm Gait (SCB) |
 |
Its motion resembles that of an
earthworm. Segments expand and contract in sequence. Sets of four
segments have identical motions. This gait can have an arbitrary number
of segments and nodes in a chain. This gait is the best for crossing
obstacle, ditches, walls etc.
|
| Earthworm Video |
 |
At the time this video was taken, only
4 segments were built, so the rear end of the robot drags on the ground.
However, this gait can be made arbitrarily long without running into
actuator limits. Quicktime video of
earthworm locomotion ~1.2M . (this quicktime
movie uses Sorenson compression, which may not work with older plug-ins)
|
| Caterpillar Gait (SDB) |
 |
This configuration is
characterized by many small feet. Like the earthworm, it can be extended
to an arbitrary length given enough modules. This gait can carry a
larger payload than any of the previous gaits. MPEG
simulation of caterpillar ~380k
|
| Caterpillar Video |
 |
This video shows the 11 modules built
at Stanford. Quicktime video of
caterpillar locomotion ~1.1M . (this quicktime
movie uses Sorenson compression, which may not work with older plug-ins)
|
| Rolling Track(RCB) |
 |
Polypod achieves motion by
rolling like in a loop. Only four segments need to change their
configuration at any one time independent of the size of the loop.. This
gait is the most efficient one that has been implemented for Polypod.
|
| Spider |
 |
This is the only gait among those
presented here which has not been explicitly simulated or implemented on
the real robot. Locomotion would be achieved by finding appropriate
foothold locations and placing a foot using a inverse kinematics method
(ideal for highly redundant serial chains) presented in my thesis, and
then shifting weight forward and repeating the sequence.
|
Turning Gaits |
| Turning Loop |
 |
This gait like the previous one, has
segments mounted perpendicularly. This allows the gait to turn. Other
gaits like the earthworm and caterpillar gaits can achieve turning in
the same manner. MPEG simulation of turning
loop ~730k
|
| Turn in place |
 |
The Caterpillar gait can also
turn in place, though in this video, Polypod has been instructed to take
two steps forward then turn in place. This video is displayed double
time to reduce the file size. Quicktime
video of turning caterpillar locomotion ~4.0M . (this
quicktime movie uses Sorenson compression, which may not work with older
plug-ins)
|
Compound Gaits |
| Catercater |
 |
This is a combination of caterpillar
gaits arranged in a 2D array. This is an example of an articulated
combination. It is particularly well suited to carry payloads as it has
a large surface area on which to place objects. The more modules used in
this gait, the larger and heavier the objects may be. MPEG
simulation of catercater ~500k |
| Exotic Gait |
 |
This is an example of a hierarchical
combination of a rolling track and a caterpillar gait. In this case
there is only a two level hierarchy. The rolling track gait never
touches the ground, it instead essentially moves the body of the
caterpillar gait.
This type of combination is additive and can lead to interesting
effects. For example, if the caterpillar gait moves in one direction and
the rolling track moves in a different one, the robot can be made to
rotate in place or move backwards. This is shown in MPEG
simulation called the moonwalk ~380k .
The pictured configuration also shows the duality between locomotion
and manipulation, in that a locomotion gait can be used to manipulate an
object. The caterpillar gait is used to perpetually suspend the object
above the rolling track. Imagine a gymnast cart wheeling while juggling
a box...
|
| SlinkySlinky |
 |
A single chain of segments and nodes
are joined together so that every other segment moves perpendicularly to
the one it is adjacent to. The effect is as two slinky gaits
perpendicular to each other are merged together. This allows the robot
to move in two dimensions and is an example of a morphological
combination.
Morphological combinations are those which are not hierarchical or
articulated. They are characterized by one gait moving in one direction
and the second gait achieving motion in another direction.
|
