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Snake
robots are not toys. Many dedicated researchers are developing snake robots
for a variety of applications from saving lives to working in space. You may fear live snakes, but you would love a snake robot that found you buried under rubble after a terrorist bombing. Fiber optics in its nose can bring light and voice communication. Tubes can supply essential liquids for life support. What a beacon of hope it would be after the blackness of despair.
In
other applications, a snake robot may serve as a fire hose in a burning building,
or an astronaut can control a snake working in the vacuum of space. These are
just a few examples; there are many possibilities. See box. An Internet search highlights the importance and need of snake robots. Laboratories scattered around the world have developed, or are working on, a variety of snake robot designs for many diverse applications. There are as many different designs as there are researchers. Some snake robots even swim in water like live snakes. Electrical and mechanical designs dominate the technology. The designs are amazing, but very complex. LIVE
SNAKES vs. BROWN SNAKE It
would be easy to conclude that snake robot technology is well in hand and one
more snake robot will not contribute to the technology. Adding Brown Snake to
the list is reasonable because it moves like a live snake better than many of
the mechanical snakes currently under development. Its method of movement copies
a live snake, which is lifting and setting down, so traction on irregular or
rough surfaces is not a problem. An outstanding feature of Brown Snake is its
simple construction, which will make it cheap to manufacture. An inexpensive
snake would greatly broaden its appeal for many applications, especially in
cases in which it is only needed occasionally. Training to use it is not
required, for even a child can operate it. It
helps to consider how live snakes manage so well without legs. Snakes move in
several different ways, but rectilinear (a straight line) locomotion is the
method Brown Snake employs. A popular name for this is the inchworm mode. Compared to an inchworm, the lifting loop a snake
makes is so small it is usually quite difficult to see. Locomotion for both a
live snake and Brown Snake is accomplished by lifting and setting down. If
lifting and setting down is a smooth motion, it will appear as a traveling wave
or rolling motion. Design parameters fix the radius of the wheel. See Fig. 1.
Fig.
1. How Brown Snake moves. HOW
BROWN SNAKE Brown
Snake is driven hydraulically (or pneumatically), which eliminates the need for
complicated electrical or mechanical devices, and even more complicated
electronic control services. The entire Brown Snake is flexible. Directing the
nose (by means not shown) permits it to turn right or left, or up and down. It
is squeezable for adjusting to all surfaces and tight passages. An external pump
supplies constant fluid pressure and a control valve routes the fluid flow to
manage speed and direction (forward or backward). The entire system is simple
and cheap enough to be a toy. Describing
Brown Snake is confusing because each segment is continuously alternating its
function from load bearing to non-load bearing. It is even hard to label parts
because in the next instant a segment will be functioning in a different mode.
All the while, the entire system is moving forward (or backward), which, of
course, is why we want a snake in the first place. It seems to wiggle away from
our ability to track what is going on. Four control tubes pass through all segments, but only one tube is open to any given segment. Each control tube is assigned to control every fourth segment. All control tubes sequence through high pressure, no pressure, and low pressure (or suction). The external pump (not shown) circulates the same fluid continuously in a closed system and no new supply of fluid is needed (as with an automobile engine). At a given instance, a control valve sucks fluid from low pressure segment 1b to supply high pressure segment 1a. In a later instance, the flows will be reversed. When tubes 1a and 1b are active, tubes 2a and 2b are inactive and vice versa. See Fig. 2.
Fig. 2. Brown Snake
is composed of segments. The numbers above each segment indicate the control
tube that drives that segment. Each control tube will control every fourth
segment. The lower view shows a single segment when expanded and when
contracted. Clockwise
or counterclockwise rotation of the control valve impeller controls whether the
traveling wave is going forward or backward. The external pump (not shown)
maintains constant inlet and outlet pressure. In Fig. 3, it can be seen that all
control tubes are sequenced through high pressure, no pressure, and low pressure
(or suction). The pressures of outlet and inlet tubes remain constant throughout
the sequences.
Fig.
3 Cross section of the Control valve and isometric of impeller. FABRICATING
BROWN SNAKE There
is never just one way to fabricate such devices, but one possible way is as
follows. 1. Select for Brown Snake’s skin a thin flexible material. See Fig. 4. 2.
Mold or fabricate segment
partitions out of the same, or similar, flexible material. The top edge of the
skin and the perimeter of the partitions may have a heavier rib to facilitate
bonding. 3.
Draw the control tubes through one
partition to mark the starting point. 4.
Draw the tubes through all the
other partitions and confirm that control tube vent holes are in their proper
position and sequence. 5.
Bond tubes to the partitions. 6.
Wrap the outer skin around the
starting partition and bond the skin to itself. 7.
Bond the skin to the second
partition to complete the first segment. 8.
Do all other segments the same, one
at a time. A minimum of eight segments are suggested, but twelve might yield a
better test of concept.
Fig.
4. Fabricating Brown Snake. APPENDIX To
simplify the above descriptions, conduits housing fiber optics, wires, tubes,
and other useful items were omitted. Many other sophisticated additions, such as
a radio controlled guidance system are possible. Self-contained robots with
built-in pump and control valve are possible depending on the application. If
the control tubes are bundled near the center of the partitions, the traveling
wave will appear as a uniformly distributed bulge surrounding the snake.
Envision an ostrich swallowing tennis balls. This may be desirable for some
applications, for example, inspecting and climbing in pipes, fire hoses, and
medical applications. A large tube through the center of Brown Snake would not
interfere with the snake’s operation, and the presence of the snake would not
interfere with the normal flow of fluids. An example would be inspecting a water
or sewer line. Brown
Snake’s requirements are modest. Assume each segment is 2 inches in diameter
and 3 inches long. It has a bearing surface of ~3 square inches. Therefore, a
pressure of 2 psi will support 6 pounds; more than enough for many Brown Snakes.
The control valve only directs flow and does not do any work. The control valve
impeller should be a close fit in its housing, but a small leakage around the
impeller may be ignored. One revolution of the control valve’s impeller will
complete a pressure sequence of the segments. Therefore, since there are four
segments, the Brown Snake will move 1 foot for every revolution of the control
valve. A hand crank may be preferred for some applications. A
few items from Home Depot indicate that the cost of constructing Brown Snake
need not be large. Fig. 5. Machining the impeller for the control valve is
likely to be the most expensive part. A 2-inch Schedule 40, IPS pipe nipple,
bored smooth for a custom fit with impeller, could serve as housing for the
control valve impeller. All tube fittings should be installed before boring. A
thrust bearing should be on the outlet end of the impeller to resist the high
pressure on the opposite end.
Fig.
5. Home Depot items (control valve impeller and segment partitions not shown). Return:
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