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Robotic Inchworm Proposal

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					             Robotic Inchworm
     For Inspection of High Power Transmission Lines




                      Melissa Else, CpE
                     Soren Engbert, ME
                       Ben Lewis, ME
                     Josh Stamper, ME



                      Faculty Advisors:
Dr. Sami Khorbotly   Dr. David Mikesell   Dr. John-David Yoder




                          Fall 2008

                                                                 1
Executive Summary
       In order to provide the energy needed around the globe, electrical wires must be in near
flawless condition. When a problem occurs with one of these wires it is important to locate and repair
the source of the problem as quickly as possible. The current methods used to locate these problems
are inefficient and require a great deal of time and resources. The purpose of this project is to design
and build a ‘robotic inchworm’ device capable of inspecting electrical wires with greater efficiency and
decreased costs.
       There are multiple design constraints that must be met. The device must be capable of
autonomous travel along electrical lines while taking still photographs of the wire. It should also be
capable of efficiently navigating obstacles while performing inspections. In order to avoid
complications from the magnetic fields caused by the electrical wire, the robot must be encased in
protective materials The size of the robot is important; it must be as lightweight as possible to reduce
strain on the wire during inspection. It must be easy and inexpensive to manufacture as this device will
be designed for widespread use across the globe. Power consumption must also be taken into
account. It should use as little power as possible to promote sustainability and be able to travel great
distances before needing to be recharged. Maintainability is also an important factor. The device must
be easy to repair, yet durable enough that it doesn’t need to be repaired on a regular basis.
Photographs taken must be saved for later viewing as well. This could be done through use of on-chip
memory or removable memory storage for easy viewing on a PC at a later time. The device should also
travel at a reasonable rate of speed to maximize the efficiency of the wire inspection process.
       This design brings with it several benefits when compared to current electrical line inspections.
Currently, inspections of large scale transmission and power lines are conducted by aerial surveillance
from a helicopter or from an unmanned aerial vehicle. In both cases, video recordings of the wire are
taken and later analyzed and observed to discover possible corrosion, cut strands, arc marks,
conductor damage, lightning damage, or various other wire defects that would hinder efficient service.
If damage is found along the line, an inspector is sent back to the transmission line to complete the
necessary repairs. Aerial inspection is costly and does not always provide the degree of precision
required. The proposed design would eliminate the negative aspects associated with aerial inspection.
Cost and time would be decreased, and there would be fewer inspection errors.

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       Although the benefits associated with the design are high, there are several risks involved with
this design. This would be the first wire inspection device of its kind, meaning that it is bound to have
some noticeable imperfections. It may take time extra time and money to eliminate these issues;
however, in time the money saved will outweigh the money lost. Another risk involves technology.
New technologies are introduced almost on a daily basis, meaning that in a few years this design may
be obsolete because of new and improved wire inspection devices.




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                                                           Table of Contents
Executive Summary .........................................................................................................................   2

Problem Identification ……………………………………………………………………………………………………………….. 5

Background ………………………………………………………………………………………………………………………………… 6

Realistic Constraints …………………………………………………………………………………………………………………… 8

              Major Constraints ………………………………………………………………………………………………………                                                                       8

              Other Constraints ……………………………………………………………………………………………………… 10

Specifications …………………………………………………………………………………………………………………………….. 11

              Electrical Component Specifications ………………………………………………………………………….. 12

              General Specifications ……………………………………………………………………………………………….. 12

Implementation …………………………………………………………………………………………………………………………. 13

              Camera ………………………………………………………………………………………………………………………. 13

              Robot …………………………………………………………………………………………………………………………. 13

Design Options …………………………………………………………………………………………………………………………… 14

Validation Plan …………………………………………………………………………………………………………………………… 15

Budget ……………………………………………………………………………………………………………………………………….. 17

Deliverables ……………………………………………………………………………………………………………………………….. 18

Conclusion ………………………………………………………………………………………………………………………………….. 18

Bibliography ……………………………………………………………………………………………………………………………….. 19

Appendices …………………………………………………………………………………………………………………………………. 20

              Gantt Chart ………………………………………………………………………………………………………………… 20

              Design Drawings ………………………………………………………………………………………………………… 22




                                                                                                                                                  4
Problem Identification


            The electrical industry expends a lot of valuable time and resources to inspect and
         maintain various types of electrical wires. When considering the inspection of transmission
         wires, this process can be very difficult when the lines are in secluded locations or areas
         where normal inspection routines are nearly impossible and extremely dangerous. Also, it is
         sometimes necessary to suspend the electric power supply to these lines during inspection,
         making the situation inconvenient for the customers involved. The goal of this team is to
         design a relatively small, unmanned robot that will “crawl” along a transmission wire
         carrying an onboard camera to record precise images of this wire. The focus of the team will
         remain on large scale transmission lines; however, consideration will be taken into the
         design for the ability to be scaled to a size that would be conducive to commercial or
         residential wire inspections.
            The robotic device created in this project will be autonomous, allowing the user to
         choose specific settings, attach the device to the wire and retrieve the data when the
         inspection is complete. This inchworm like device will attach and transport itself along the
         wire, taking still photographs of sections along the route. The frequency of photographs
         taken will be based off the speed of the robot, the amount covered in a single frame, and
         the length of the wire to be inspected. These photographs will be stored in a sequential
         order on the devices on-chip memory for later retrieval. It may be possible to incorporate
         removable Flash memory into the device for ease of transport of photographs to a PC. This
         will also provide a more flexible option in terms of memory size for various situations.
            The team will be challenged to create a robotic device that will have low power
         consumption and a low physical weight. Each of the components will need to draw as little
         energy from the battery so as to maximize the life of the battery for the actual inspection
         process. The robot will be constructed out of a light weight material that will shield the
         electronics from damage caused by the magnetic fields on the line. It will be powered by a
         rechargeable battery. The movement of the robot will be controlled by a combination of
         actuators and small motors that will aid in the maneuvering along the line and around

                                                                                                        5
     various obstacles. A computer system will be available to monitor the available storage,
     battery life, and overall status of the system. The device will be programmed to avoid
     situations of insufficient power or storage during the inspection.
         To combat environmental concerns, the body of the robot will be made out of a
     recyclable material and the power supply will be a rechargeable battery with specific
     recycling instructions. Details of all the realistic constraints will be discussed at a later point
     in this document. Another important trade off this team will consider is between size and
     functionality. A product cannot exist without considerable change in parts to inspect both
     residential and transmission wires. Also, a robot inspecting a transmission wire would need
     to be considerably larger than a robot for the inspection of residential wiring due to the
     nature of the obstacles the robot would need to overcome.
         Testing of this robot will include both non-current and current conducting wires. Once
     the device is proven capable of crawling along a non-current conducting wire, it will be
     tested in more realistic environments to ensure the safety of the electronic devices in the
     presence of magnetic fields.


I.   Background
         Electric energy is supplied across long distances in the electric power grid via
     transmission lines carrying high voltages and large amounts of power. Three types of
     transmission lines exist for this purpose including overhead, subtransmission and
     underground transmission wires. Overhead transmission lines carry extremely high voltages
     ranging from 69KV to 765KV and cover large distances. Subtransmission lines carry a
     reduced amount of these voltages, typically 34.5KV to 69KV, supplying some large
     commercial or industrial operations. Underground transmission wires are generally used in
     populated areas where overhead lines would be impossible to implement. The types of
     power lines that are most commonly visible are known as distribution lines. These lines




                                                                                                           6


                      Figure 1: Electric Line Tower Structures
supply the reduced voltages to the residential and smaller commercial areas. Figure 1 shows
the various towers associated with each of the previous transmission lines.
   Currently, inspections of large scale transmission and power lines are conducted by
aerial surveillance from a helicopter or from an unmanned aerial vehicle. In both cases the
process consists of two phases: video recordings of the wire followed by analysis of the
frames to discover possible corrosion, cut strands, arc marks, conductor damage, lightning
damage, or various other wire defects that would hinder efficient service. Some inspection
routines will record the entire specified length of the wire, under the assumption that a
missing frame would be the same as overlooking possible line damage. Other inspections
rely heavily on the discretion of the operator who flies the experienced electrician along the
wires and records images of only those areas that would need more in-depth analysis. Both
routines are highly dependent on the expertise of the electrician involved in the
maintenance when the analysis stage is performed.
   The data recorded from the initial inspection is transferred to a personal computer for
analysis. Some researchers are currently working to develop software for the automatic
analysis of this returned data. One specific program currently developed has the ability to
detect automatically damage to a wire caused by lightning, such as arc marks or cut strands,
by plotting brightness and the upper and lower contours of the wire. These plots are then
analyzed and detection results are then reported back to the operator.
   If damage is found along the line, an inspector is sent back to the transmission line to
complete the necessary repairs. This part of the maintenance process may require the
power supply of the transmission line to be temporarily suspended due to the dangerously
high voltages and currents the line carries.
   In conclusion, aerial inspection is costly and does not always provide the degree of
precision required. It is a method highly dependent on the expertise and opinion of the
electrician conducting the inspection, creating variable results. A few examples of robots for
the inspection of large scale transmission wires have been researched and prototyped;
however no evidence was found to suggest that these robots are currently being used in
industry today. However, similar designs were found currently in use for different


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      inspection applications. U.S Patent # 7303010 describes a wormlike device used for
      inspecting oil pipelines. This design utilizes the flow of oil for propulsion but uses a similar
      inspection method to that of the proposed inchworm. U.S. Patent # 7375801 describes a
      mobile camera base used for inspection tasks in small areas, specifically the hardware on
      space vehicles. This device uses a multi-component camera system to capture images while
      the base moves.


II.   Realistic Constraints
      Accreditation Board for Engineering and Technology Requirements
      The Accreditation Board for Engineering and Technology has set requirements that must be
      met by all engineering students. These requirements are that a student must demonstrate
      the ability to design a system or component to meet desired needs while complying with
      realistic constraints. In completing this project, the Robotic Inchworm team will show just
      that. The team will use the five step approach to problem solving throughout the project.
      The proposed inchworm will meet constraints that deal with economic, environmental,
      health and safety, and manufacturability issues.
      A. Major Constraints
         Economic
                 Since the size of this robot is a concern, it is important to consider the size of all
             the components that will be used. Typically as the size of microcontrollers, batteries,
             and other electronics decrease, the cost to purchase these components increases. It
             will be necessary to compare prices of similarly sized products to see if the overall
             impact on the final size of the robot will be enough to purchase the smaller, more
             expensive piece.
                 One of the major economic concerns for this project is the theoretical expense
             to fund the research and construction of this robot. Since this is a concept that has
             not yet been implemented in the electrical industry, much research must be
             completed to make sure all bases are covered. Specifically for this senior design




                                                                                                          8
   project, there will be a four member team completing the research necessary for the
   construction of the project over a course of twenty-five weeks.
       All of these previously discussed concerns play a role in the main economic
   consideration of this design project: the cost of the final product to the consumer.
   This robot is being design so that it can replace the process of manual inspection by
   trained electricians. In order for this new robot technology to be used in the
   industry, the cost of implementation must be significantly lower. While the initial
   cost to purchase the robot may be high, over time it will decrease, generating a
   lower final cost to the consumer.
Environmental
       The affect of this robot on the environment is another constraint that must be
   considered during this design process. The team members on this project are
   considering the environment in terms of power supply and in the material used to
   build the robot. The power supply will be a rechargeable battery with a specific
   disposal plan. Since rechargeable batteries are being used, there will not be as much
   waste as there would be when normal batteries run out. The team will also use
   recyclable materials to build the body of the robot. Currently, aluminum is the
   material of choice. Any scrap material that is not used in the robot’s construction
   will be recycled.
Sustainability and Maintainability
       Proper documentation will be provided so that the user knows how to properly
   care for the robot in order to extend its lifecycle. Since this is essentially a
   contracted project, the developers will not be around after the final product is
   delivered to perform maintenance. Because of this, the final deliverable needs to be
   reliable and easy to maintain. If the battery no longer maintains a charge, it must be
   easily accessible so that it could be properly disposed of and replaced.
       Since this robot may be subject to harsh weather conditions such as cold
   temperatures, high wind velocities, or moisture, measures need to be taken to
   prepare the robot for these situations. The ability for the robotic arms to detach and


                                                                                           9
      reattach to the wire in cases of high winds is an important constraint to consider.
      Also while the entire body of the robot may not be waterproof, it should be able to
      remain functional in humid or damp conditions.


B. Other Constraints
   Manufacturability
             If the robot were to be mass produced in the future, it will be important to
      consider the complexity with which the components of the robot are assembled.
      The design could be adapted to use components that are already on the market.
      Rather than having a circuit board made specifically for this robot, one that has all
      the necessary functionality could be adapted and used. Since a rechargeable battery
      will be used, it will be beneficial if it is adaptable to an already manufactured
      charger.
             When it comes to attaching this robotic inchworm to the actual transmission
      wire, this will only be possible in one direction. Otherwise, the constraint will be
      placed on the team to also design the robot so that no matter what orientation it is
      placed on the wire, it will be able to function.
   Ethical
             It is very important to consider all resources where information was gained. All
      authors of articles, patents, and websites will be given sufficient credit for their
      contributions to this project. All manufacturers of the parts being used will also be
      given credit for their contributions.
             Another ethical constraint that must be overcome is to make sure that the robot
      will not have the ability to be used for any function other than that which it was
      initially intended. Since this is an autonomous device with the ability to take
      photographs, the ethical concern may arise that this robot could be used as an
      intrusion of privacy. To avoid this concern, it may be possible to narrow the line of
      vision of the camera lens so that only pictures of wires or other thin objects will be
      possible.


                                                                                                10
          Health and Safety
                  This robot will be designed so that it will remove the electricians from certain
              dangerous situations, like climbing along a significant distance of the wires. It is very
              important that we also take into consideration the high amount of energy associated
              with these transmission wires. The robot will need to ground itself in some way once
              touching the wire so as not to send an electric shock to the electrician who puts it on
              the line.




III.   Specifications
          One goal of the project is to make the inchworm as small as possible; still, in order to
       perform the required tasks, the device must be physically larger. By design, in order to
       travel around an obstacle, the device will have to “reach around” the obstacle and grab the
       wire on the other side. This means that the device will have to have an arm that is at least
       as large as, or can extend to be as large as, the obstacles it will face. Due to the larger size
       of the device, larger motors and actuators will be required which, in turn, will require a
       larger power source. The base function for the device will be to attach to a transmission
       wire and travel along its length, while capturing and storing images in an on-board memory
       unit. The secondary function for the device will be able to traverse around obstacles, not
       exceeding the given size listed above. The device must also be able to account for
       interference from the electric and magnetic fields generated by the wire. This will be done
       by adding aluminum shielding to the electrical components on the device. The device will
       also have to take wind into account when traversing the wire. The clamps will have to be
       extra powerful to be able to hang on to the wire during a strong wind, but there may have
       to be a maximum operational wind speed restriction.




                                                                                                      11
A. Electrical Component Specifications
      Two camera chips used to capture both the top and bottom of the wire
      Images stored in on-chip memory
          o Option: Images stored in removable Flash memory
      Atmel microcontroller used to control the motors, actuators, and other mechanical
       parts of the robot
      Coding completed in high level language such as C
      Program code will be completed in limited memory – limited to the amount of on-
       chip memory of the microcontroller less the amount needed for picture storage
      Microcontroller will be programmed to monitor battery life and available memory
      Camera lens will have ability to be posed to gain a better view of wires
B. General Specifications
             Wire diameter: 0.8’’ - 1.4“
             Maximum size of obstacle: 8’’ wide x 4’’ tall
             Maximum speed: 6“/second
             Weight: about 7 lbs
             Power Consumption: 12V per motor, about 3V per linear actuator
             Overall Length (with arms extended): 30”
             Length of Extended Arm: 12”
             Overall Height (hanging from wire): 8”
             Range: TBD
             Time to Recharge Battery: TBD
             Time to Manufacture: TBD
             Camera Specifications: 3 Megapixel
                            15 frames/second
                            Max Resolution: 2038x1536
                            Power consumption: 75mA (active)
                                                20µA (Standby)
                            Output Format: YUV raw RGB data or RGB compressed data

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IV.    Implementation
       A. Camera
            The microcontroller will be programmed using a high level language to signal the
            camera chips to photograph the wire at a specified time interval. This interval will be
            determined by calculations based off the speed of the robotic inchworm and the length
            of wire covered in one image. These images will be stored in sequential order on the
            memory. This memory could be on-chip memory included in the microcontroller or it
            could be removable Flash memory in the form of a compact flash card. The transfer to
            PC is simplified if the memory is a compact flash card since most computers have built in
            card readers. If the images are stored in the on-chip memory of the microcontroller, a
            connection will need to be established between the robot and the PC, a USB connection,
            for example. Both memory options will have a storage limit and will be able to be erased
             after images are transferred to the PC so the memory can be cleared and used in later
            inspections.

      Camera
        1
                                                      Memory




                                Microcontroller



        Camera
          2



 Figure 2: Block Diagram for Camera Function


       B. Robot
            The main concern with the inchworm is the ability to stay attached to the wire. To
            accomplish this, either springs or clamps will be used to apply the necessary force to the
            wire. Since there is a range of wire diameters that have to be designed for, different size
            wheels and clamps will be used. The operator will be required to change the wheels or
            clamps to fit the desired wire. The operator will also need proper training and safety
            precautions must be followed to climb the wire towers and attach the inchworm to the

                                                                                                      13
        wire. In the case where the inchworm is unable to avoid an obstacle, the operator will
        be required to climb each tower to move the inchworm around obstacles. If there are
        obstacles between the towers, the inchworm will have to go to the obstacles, return,
        and come from the other side. The required maintenance for the inchworm will be
        oiling bearings and other moving parts and replacing springs and battery packs once
        they are worn.



V.   Design Options
        Three viable design alternatives have been chosen to solve the wire inspection problem.
     The first design uses three arms that pivot at the base. The arms are attached to the wire
     with spring loaded wheels above and below the wire and the motors are mounted above
     the wire. Two of the arms will house drive motors while the middle arm can roll freely. Each
     arm will have an electric linear actuator connected to it from the base. The linear actuator
     will provide the power needed to push the wheels off the wire and to lower the arm around
     obstacles. Once free of obstacles, the linear actuator will retract and pull the arm onto the
     wire. The camera will be mounted on one of the arms so it will be close to the wire. The
     microcontroller and battery will be mounted on the base, away from the wire. All electrical
     components will be shielded with aluminum to block interference created by the
     electromagnetic field around the wire. This design is approximately 20 inches long and 12
     inches tall. The design can accommodate obstacles that are less than seven inches long with
     no more than eight inches below the wire. The device will travel on wire diameters ranging
     from 0.75-1.5 inches using different wheel sets for various wire sizes.
        The second design uses one drive wheel to power the inchworm. There are two guide
     wheels on the opposite side of the wire that provide both support and the necessary force
     needed to keep the drive wheel from slipping. The guide wheels use springs to stay on the
     wire. The springs allow the guide wheels to move outward to avoid obstacles. The motor
     and drive wheel are mounted above the wire and the guide wheels are below with the
     battery, camera, and microcontroller. The majority of the inchworm is mounted below the
     wire to take advantage of gravity to stay on the wire and to help with traction. This design is

                                                                                                    14
      approximately 5 inches long and 5 inches tall. The inchworm will be able to overcome
      obstacles that are less than two inches in diameter that do not fully encompass the wire.
         The third design uses two sets of clamps to grip the wire for stability and for motion.
      The drive mechanism uses a long arm to reach in front of the inchworm. Once extended, a
      clamp will secure the wire and the arm will retract, pulling the inchworm forward. A set of
      wheels located in the center of the body will ride on the sides of the wire to stabilize the
      device while in motion. On the opposite end a second arm and set of clamps will secure the
      wire when the drive mechanism is moving freely. The drive arms will be powered by electric
      linear actuators and will pivot in the center. The arms will move below the wire to avoid
      overhead obstacles. The forward and rear arm will move simultaneously to maximize speed.
      The camera, battery, and microcontroller will be mounted on the main body of the device,
      directly below the guide wheel. The arm will extend 10 inches in front of the device and the
      overall length will be 30 inches.



VI.   Validation Plan
         Before completion of the inchworm, several forms of testing will take place. The first
      test will use finite element analysis software. This form of testing will be performed to
      insure the design can handle the required forces to keep the inchworm on the wire. The
      maximum wind speed for safe operation can also be calculated from these tests. The FEA
      software can be utilized to determine if certain components of the design will function as
      desired. These tests will be performed before the parts are purchased and assembled.
      Once the design is constructed, physical testing will begin. The first test will use wires
      suspended above the ground that have no power running through them to test all the
      functions of the inchworm for the range of wire size. Obstacles will be added to the wires to
      represent situations the inchworm will face once in service. The obstacles will range in size
      and geometry to guarantee the inchworm meets the design requirements. Once it has been
      shown that the inchworm can maneuver around obstacles, the next test is for the life and
      range of the inchworm. The range both with and without obstacles will be found. The
      results of this test will also show how much memory is needed for inspection over the life of

                                                                                                     15
the battery. These results can also be used to make adjustments in the picture rate or with
video storage. Once it has been confirmed that the inchworm works properly, a working
environment test is next. To accomplish this, the inchworm will be placed on a transmission
wire with full power running through it. The inchworm will first move along the wire
without any obstacles. Once this test has been satisfied, the inchworm will navigate around
obstacles. The final test will involve a wind speed test. The maximum wind speed where
safe operation is still apparent will be found. This will be compared to the calculated values
and changes will be made if necessary.




                                                                                            16
VII.   Budget

                   Estimated Budget for Robotic Inchwormers
                                                        Unit     Total
          Component                            Quantity Price    Price
          motors                                      1   $25.00    $25.00
          servos                                      2   $15.00    $30.00
          actuators                                   2   $60.00   $120.00
          wiring (per foot)                         15     $0.70    $10.50
          Aluminum (per pound)                        6    $4.00    $24.00
          wheels                                      2    $4.00     $8.00
          CMOS Camera Chip                            2   $30.00    $60.00
          camera lens                                 2   $15.00    $30.00
          Atmel Microcontroller                       1   $50.00    $50.00
          impact whisker sensors                      2    $6.00    $12.00
          rechargeable lithium battery                1   $35.00    $35.00
          2GB memory card                             1   $15.00    $15.00
          removable Flash memory (RW) device          1   $50.00    $50.00
          voltage regulator                           1   $20.00    $20.00
          transistors                                 2    $0.50     $1.00
          capacitors                                  2    $0.20     $0.40
          resistors                                   2    $0.20     $0.40
          extra/replaced parts                 -         $100.00   $100.00
          shipping                             -         $100.00   $100.00

                                                         TOTAL:     $691.30
          Theoretical Labor Costs:
                                                Hours    $$/Hour Qtr Total
          Fall                                     100     $35.00 $3,500.00
          Winter                                   250     $35.00 $8,750.00
          Spring                                   100     $35.00 $3,500.00

                                               TOTAL LABOR COST: 15,750.00




                                                                              17
VIII. Deliverables
      The following is a list of deliverable items broken down into the quarter in which they will
      be completed.
         Fall Quarter
                 Fall Project Proposal
                 Proposed budget
                 Gantt chart
                 Oral proposal report
                 Weekly progress reports (Emails)
         Winter Quarter
                 Weekly progress reports (Emails)
                 Preliminary Robotic Inchworm
                 Testing and Validation Results
         Spring Quarter
                 Final Robotic Inchworm
                 User’s manual / documentation
                 Final oral presentation
                 Final Poster


IX.   Conclusion
         This proposal outlined potential designs for an autonomous robotic inchworm which will
      be used for electrical wire inspection. The purpose of the design is to replace the current
      inefficient and expensive methods of electrical wire inspections. Different factors included
      in the design process were size, weight, power consumption, reliability, speed,
      maintainability, cost, ease to build, obstacle avoidance, and size of obstacles which can be
      avoided. After considering all these factors, the top designs were chosen through the use of
      a decision matrix and Pugh’s method. From these top designs the final design will be
      chosen and made into a working prototype.



                                                                                                     18
                                         Bibliography
1. US Patent #7375801
   2008 May 20
   Briscoe, Jeri M., Corder, Eric L., Howard, Richard T., Broderick, David J.
   Video Sensor with Range Measurement Capability
2. US Patent #7303010
   2007 December 04
   Guzman, Neil D., Lafferty, L., Lafferty, C., Steinman, Donald K.
   Apparatus and Method for an Autonomous Robotic System for Performing Activities in a Well
3. The Robot Marketplace
   Accessed October 15, 2008
   http://www.robotcombat.com/store.html
4. United States Department of Labor
   Accessed October 17, 2008
   http://www.osha.gov/SLTC/etools/electric_power/illustrated_glossary/transmission_lines.html
5. Ishino, R. and Tsutsumi, Dr. F. CRIEPI’s Aerial Inspection of Transmission Conductor.
   Transmission and Distribution World.
   www.tdworld.com/December_2004
6. Nayyerloo, Mostafa. Yeganehparast, Seyyed Mohammad Mehdi. Barati, Alireza. Foumani,
   Mahmud Saadat. Mechanical Implementation and Simulation of MoboLab, A Mobile Robot for
   Inspection of Power Transmission Lines. International Journal of Advanced Robotic Systems. Vol
   4, No.3 (2007) pp 381-386.

7. Sawada, J. Kusumoto, K. Maikawa, Y. Munakata, T. Ishikawa, Y. A Mobile Robot for
   Inspection of Power Transmission Lines. IEEE Transactions on Power Delivery. Vol 6, Issue 1. Jan
   1991. p 309-315.




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