CHIMAERA: Motivation, Design and Construction

Transcription

1 CHIMAERA: Motivation, Design and Construction Rudnei Moran, Giuliano Grahl, Julian Sellan, Daniel Pena, Sabri Tosunoglu Department of Mechanical and Materials Engineering Florida International University West Flagler Street Miami, Florida ABSTRACT In this project, an underwater ROV named Chimaera is designed and built to compete in the M.A.T.E. International Competition 2016 located at the NASA s Johnson Space Center Neutral Buoyancy Lab (NBL). The Explorer Class is the category in which Chimaera will compete as this is the 4-Year University Class and very specific design guidelines are set to receive maximum points for the competition. Such as, a weight restriction to under 17 kilograms and a total diameter of less than 58 centimeters. Chimaera will be a one of a kind, dual-purpose ROV poised to deploy on a mission to space, particularly, to Jupiter s moon, Europa. Many tasks need to be accomplished within the given time limit that will test engineering prowess in terms of design, feasibility and accessibility. Several obstacles must be overcome in the design of this ROV as a very intricate circuit must be designed to handle the immense power supply that is given, a lightweight yet strong structure must be created to handle the rigors at sea and a Graphical User Interface (GUI) will be created using LabVIEW without any prior knowledge of said program. Therefore, this project will be a growing pain that will allow four young engineers to gain intangible experience in the very difficulties that industry engineers face on a day-today basis. Also, participating in an International Competition could provide major exposure for a rising university such as FIU to not only participate but compete at a National level. Finally, not only will this project allow for rapid growth in terms of real-world experience of engineering with boundaries set in place but allow for the growth of South Florida s #1 University in the realm of robotics, ultimately providing more outreach to stimulate more students to pursue a career in STEM. Keywords Remotely Operated Vehicle (ROV), Robotics, LabVIEW, M.A.T.E. 1. INTRODUCTION 1.1 Motivation In 1978, the National Aeronautics and Space Administration (NASA) launched the first civilian oceanographic satellite in an effort to study and explore the vast ocean. To this day, there is still so much mystery in the deep blue sea that scientists and engineers are trying to unveil. With the use of remotely operated vehicles (ROVs), man can descend into unimaginable depths to discover what lies beneath while never putting a human life in danger. This is the challenge in which our team will dive into. With several challenges tailored to challenge college students to design, manufacture and perform an ROV in different ways, the Marine Advanced Technology Education (MATE) Competition fits our ambitions to test our team s knowledge and creativity in a real-life application towards discovery. The 2016 M.A.T.E. Competition will include a new horizon never before seen in previous challenges. It will include specifications for this ROV to have survivability in extreme conditions on Jupiter s moon, Europa; all while being capable of returning qualitative data on the ice crust, as well as, the ocean beneath it. For all the above reasons, our team has decided to pursue a project that enables the desire towards life-long learning, challenges our capabilities in engineering and will make a longterm impact on future discovery. 2. PROJECT FORMULATION 2.1 Project Objectives The major goal of this project is to be invited to compete in the next level after the Regionals in Tampa, FL. At the Regionals and at NASA s NBL, the tasks that need to be accomplished will be the same. Nevertheless, the stakes are much higher when the final stage is reached. The tasks that need to be successfully accomplished in both design and performance are listed as follows: Mission to Europa o Measure the temperature of venting fluid o Determine the thickness of the ice crust o Determine the depth of the ocean under the ice Mission-critical equipment recovery o Survey the seafloor to find and identify missioncritical NASA equipment o Place the equipment in a collection basket for retrieval by a crane Proceedings of the 29th Florida Conference on Recent Advances in Robotics, FCRAR 2016, Miami, Florida, May 12-13,

2 Forensic fingerprinting o Collect and return two oil samples to the surface o Analyze a gas chromatograph of each sample to determine its origin Deepwater coral study o Photograph corals and compare to images to previous years to assess their condition o Collect coral samples and return them to the surface Rigs to reefs o Attach a flange to the top of a wellhead o Secure the flange with bolts supplied o Install a cap over the flange o Secure the cap with bolts supplied All above tasks will need to be accomplished in order to pass the Regional tests and be invited to the Neutral Buoyancy Lab in Houston. Instructional videos and particular details of the competition tasks will be released on November 15, 2015 in order for teams to design appropriately for the tasks Design Specifications i. Size and Weight ROVs are limited to a maximum diameter of 85cm. All ROVs must be capable of a hand launching into the pool in which they will be assessed during performance demonstration. Additional design points will be given to the team if the size of the ROV is less than 58cm in diameter and weighs less than 17 kg. ii. Materials All materials chosen for the ROV will be waterproofed and capable of withstanding the pressure at a depth of up to 12.2 meters. iii. Tether Length Tether length must be calculated to include being placed no more than 3 meters from the pool in which the demonstration is being held, must be capable of operating at a maximum depth of 12.2 meters and finally, the demonstration will take place no further than 10 m from the edge of the pool. iv. Vehicle Deployment and Recovery The ROV must be manually inserted and recovered from the pool by hand. Therefore, use of mechanical mechanisms to lift heavier load such as winces or portable cranes may be used. v. Propellers Propellers must be covered at all times, to include pre-inspection and up till the demonstration is complete. If the propeller blades are exposed without a shroud (extending at least 2cm in front and behind), the ROV will not meet safety inspection and be disqualified. vi. Electrical The MATE battery supplied will be a nominal 48 VDC. No power modifications will be conducted until the voltage reaches the ROV system bus. Any power conversions that are made on the top side of the tether will disqualify the team from continuing in the competition. To adhere to safety, no power conversions once aboard the ROV, will be jumped up passed the maximum allowable voltage of 48 volts. Therefore, any electronics or sensors that require high voltage will be discarded in Chimaera's design. Voltage spikes that are seen when solenoids or motors are switched off/on will not be penalized and the team will not be disqualified; the team will, however, be required to design around the spikes as they can be a safety hazard and cause a short circuit. vii. Current Based on the maximum current draw of the ROV, the system must have a fuse (or circuit breaker). Overcurrent must be calculated using the following formula: Overcurrent Protection = ROV Full Load Current * 150% Using the overcurrent protection equation, the fuse used will be rounded up to the next standard fuse for safety. The System Interconnection Diagram (SID) must show the position of the fuse or circuit breaker and the calculations of the overcurrent protection. The ROV will be protected by a 40-amp fuse provided to the team by M.A.T.E.. Nevertheless, the circuit onboard the ROV will also require its own fuse. viii. Control Systems All control systems are expected to be computer (or electronic) based methodologies, as well as, H-Bridge or BLDC controllers for the thrusters. If the control station wires are not neatly presented, the ROV will not pass safety inspection and the competition will be forfeited. ix. Command, Control & Communications (CCC) a. Power Provided An AC power source will be provided on the surface via an outlet for video monitors and control boxes. At no time can this power source be used to power any components onboard the ROV. b. Displays Teams are not limited to the amount of displays necessary for the ROV. In fact, any other forms of displays that include laptops, TVs or computer displays are encouraged and left to the discretion of the team. Once again, any additional displays must use the AC power source provided Constrains The MATE competition itself sets several constraints on the ROV. The idea is for the ROV to be able to maneuver through a hole in a sheet of ice on Jupiter s moon, Europa. The maximum size of the ROV must not exceed 85 centimeters; any vehicle exceeding these size dimensions will not be allowed to compete. Also, current design specifications will limit the diameter of the ROV to 58 centimeters. This lightweight and small ROV will gain extra design points during the competition. The second requirement is that the ROV must be able to operate at a depth of 12.2 meters, which implies that one, if not more, of the tasks must be completed at this depth and the ROV must be able to withstand the applied pressure in this position. Lastly, the power supply provided by the competition is a 48-volt, 40-amp DC power supply. The competition manual states that all voltage conversions must be done onboard the ROV and not topside. These requirements are set forth by the competition committee and must be followed in order to compete at the regional event. With all the required constraints in mind, it must also be considered that the ROV is going to be powered by electrical Proceedings of the 29th Florida Conference on Recent Advances in Robotics, FCRAR 2016, Miami, Florida, May 12-13,

3 components and must be sealed properly in order to avoid shorting the entire ROV while it is under water and losing control. NASA pays approximately $20,000 per kilogram that is launched into space and for this reason, it is of critical importance to limit any weight on the ROV that is not deemed mission essential. Also, this specific weight restriction is unique to the 2016 M.A.T.E. Competition and will be given extra points if the ROV designed is under than 17 kilograms. 3. DESIGN ALTERNATIVES 3.1 Design Alternative 1 The first design taken into consideration was intended to be as simple and cost effective as possible. This would be accomplished by using the least amount of material and components as possible. Figure 1, shows a model of the first design. As can be seen, the design was heavily influenced by submarines. While simple and cost effective, there are many disadvantages of incorporating this type of design. The Figure 1. Preliminary Design most obvious component missing from this design is a frame. Without a frame, the ROV is exposed to many potential hazards which could result in costly repairs in the long run. The design also does not allow for components to be added later on if need be. This was crucial for the ROV due to the fact that later developments of the ROV were desired in order for improvements to continuously be made. 3.2 Design Alternative 2 From the first design alternative it was learned that a frame was going to be necessary to incorporate into the final design. For this reason, a PVC structure was added around the central pressure canister. A model of the second design can be seen in Figure 2. While this design does a great job of protecting the central pressure canister where all the electrical components will be located, the thrusters are still placed externally and are still vulnerable to damage. The PVC structure, while lightweight may not be able to handle the vibrations for the thrusters during operation. This vibration would cause small cracks in the PVC causing them to fill up with water and sink the ROV thus losing maneuverabil ity. Further changes needed to be made in order for all the ROVs compon ents to Figure 2. Secondary Design be protected as well as ensure the chassis will be able to handle the loads of the ROV during operation underwater. 3.3 Design Alternative 3 The third design was extremely similar to the second in the regard that the same design geometry was used. Rather, for this iteration the base of the ROV was to be constructed of aluminum rather than PVC as can be seen in Figure 3. The aluminum base gives the ROV more strength at the base of the structure. While there were concerns with the PVC on the last design, the thrusters on this design are mounted on the Figure 3. Proposed Design aluminum which would be able to handle the vibrations much better than the PVC which would result in no chassis failure. The only problem that can be seen in this design is how the PVC structure will be mounted to the aluminum base as there are no brackets that can be used because it will damage the PVC. The ROV would also always need to be carried from the base because the PVC cage would not be able to sustain the weight of the ROV and would result in structure failure as well as potential damage to ROVs components. Fortunately, in order to avoid any potential obstacles, a sponsorship from Misumi USA, allowed for the final design of a frame composed of all lightweight aluminum. Giving the ROV the strength to sustain its own weight as well as staying lightweight in order to obtain more design points from the M.A.T.E. judges. 4. NAVIGATION CONTROLS Using LabVIEW for the navigation of the ROV is a visual representation of coding and is simply a matter of connecting the dots, so to speak. It is based on a transmission of data, leaving the path for the user to layout. On what is called a Block Diagram, different blocks are added and connections are made using wires. The thrusters that were purchased from BlueRobotics operate with an Electronic Speed Controller (ESC) and receive signal to move from Pulse Width Modulation (in s). For this reason, the thrusters use the exact same LabVIEW MakerHub Open, Write and Close commands (icons) as the manipulator arm. Figure 4. LINX Initiate/Open Servo As shown above, the Open Servo icon in LINX connects to the initiation of the LINX system and then the channel is specified. This channel that is specific for each thruster must be a PWM channel on the microcontroller that is being used. In this case being that the Arduino Mega 2560 is the microcontroller, channels 2-13 are capable of sending PWM signals and are therefore the channels set in the command Block Diagram in LabVIEW. Once Proceedings of the 29th Florida Conference on Recent Advances in Robotics, FCRAR 2016, Miami, Florida, May 12-13,

4 the signal for the PWM is open in the specific channel set, the signal must be written to the servomotor or ESC. This is completed by using the Servo Write command found in LINX. their respective functions, offering quick thruster response at the flick of a finger. Table 1. Analog Joystick Values Figure 5. LINX Write (PWM) Servo In Figure 5, the servo channel must remain as indicated in the Servo Open command and the control for the Pulse Width (in microseconds) can be set. Multiple servomotors or ESCs can be paired into one control based on the maneuverability needs of the ROV. Lastly, the servo motor must be closed along with LINX for the program to run smoothly. Below are figures of the Block Diagram operating Chimaera and allow for a visual representation of how all the channels were used for navigation. Figure 6. Block Diagram In Figure 6, there are control modules that are denoted as Left Turn, Right Turn, etc. These are visual controls for the ROV and are shown on the Front Panel and is the GUI that will be used when Chimaera is in operation. On this panel, all controls of the thrusters and manipulator are conveniently on one screen and allows for ease of use. This front panel will be coupled with the Serial Monitor from the Arduino software (I2C Sensor) and the camera so the driver of the ROV can have all available information on this screen. Navigation controls are determined by type of signal received from the USB Joystick. Both the servo motors and thrusters operate within certain PWM ranges, therefore if the joystick were to send default signals out of acceptable PWM range, nothing would occur. Firstly, the joystick is initialized and the program awaits inputs. Once inputs are received, they must be converted into data acceptable to the electronic speed controllers and servo motors. Figure 7. Logitech F310 Joystick Therefore, for the double analog joysticks highlighted in Figure 7, values vary both positively and negatively from a central neutral value, which in some cases is 0 and in others is A set of functions were created to return suitable values in the range of PWM, also reversing the values in the case where the ROV is to turn left and right. Joystick outputs on Table 1 were the input values for 5. POWER SYSTEMS In order to power the ROV and all its components, a 48 volt/40- amp power supply is going to be provided for teams on competition day. In order to replicate this competition like atmosphere while testing the ROV prior to the competition, a similar power supply is going to be purchased in order to ensure competition rules are being followed. A 60 foot neutrally buoyant tether was purchased in order to transmit the power from the topside power supply to the ROV. Power regulation is crucial during the design of the power system because it allows the components to function properly. In order to account for this, both Battery Eliminator Circuits (BECs) and buck converters will be used as voltage regulators in order to bring the initial 48 volts down to a more manageable voltage that will power the components without overheating. 5.1 Tether The tether is the most crucial component during the operation of the ROV, it is considered the lifeline of the ROV, without it the ROV would not receive power to any of its components rendering the ROV useless. For this reason, it was important to do extensive research on the type of tether that should be purchased for the competition. The competition manual states that the teams must be able to operate the ROV at a maximum depth of 12.2 meters and 13 meters from the side of the pool. Simple geometric calculations were made in order to see what minimum length would enable the ROV to be able to Figure 8. Neutrally Buoyant Tether maneuver every part of the competition area easily. The tether that was ultimately purchased was 18.3 meters in length and 11.2 mm in diameter. Ideally, the tether should be as thin and short as possible in order to minimize the drag force that the ROV will experience during operation. The tether includes 2 pairs of 20 gage wires to transmit power, a pair of 24 gage wires to transmit video signal, another pair for communications and the last pair for accessory use. These wires are surrounded by a special foam jacket in order to ensure that that tether is neutrally buoyant to avoid any additional applied drag forces on the tether during operation. 5.2 Power Regulation An unexpected challenge during our build phase was power regulation as it is necessary in order to power the ROV safely. Proceedings of the 29th Florida Conference on Recent Advances in Robotics, FCRAR 2016, Miami, Florida, May 12-13,

5 Since the competition class is for University level students, M.A.T.E. provides the teams with a rather large Direct Current (DC) power supply consisting of 48 volts/40-amps and expects each of the teams to drop the voltage down on the ROV in order to power its components. Since teams are being provided a DC power supply, a traditional transformer cannot be used as they are designed for Alternating Current (AC). Figure 9 shows a comparison between both DC and AC signals in order to visualize the difference. If a traditional transformer were to be used in this case, the signal would need to be inverted from a constant signal to a sinusoidal or square wave. This proved to be extremely difficult and unsafe because of how dangerous AC signals can be. It was determined that the safest route to take would be to keep DC signal throughout the ROV s power system. Since direct current is going to be used for the ROV, it is necessary to purchase some sort of DC to DC voltage converter because 48 volts is too high of a voltage for the thrusters to operate on. As was stated in the production selection section of this paper, the type of DC to DC converter being used on the ROV, is called a buck converter. A buck converter is essentially a device that takes a high voltage and brings it down to a more manageable voltage. Inside this device contains an integrated circuit that handles all of the voltage regulation. Since the buck converter would be converting such a large voltage it is assumed that the converter will give off some sort of heat. Heat sinks are typically installed inside these buck converters in order to dissipate the amount of heat released during the conversion. These types of converters would be ideal to use for the construction of the prototype. Typically, these converters would need to be installed inside of the pressure canister onboard the ROV in order to prevent them from getting wet and shorting out. This poses a problem because there is no ventilation inside the pressure canister. Even though there are heat sinks inside the converter, there is no sort of flow inside the pressure canister to cool them off so they will stay hot throughout the operation of the ROV which leads to overheating the components and thus destroying them. However, the buck converters that were purchased are waterproof which allows them to be mounted externally on the chassis and allows the heat to dissipate to the atmosphere. The majority of the components onboard will need to receive power during the entire operation of the ROV such as the Arduino and the sensors as they will constantly be running, however this is not the case for the thrusters. The thrusters will only be running when the commands are sent from the computer to the Figure 9. Signal Comparison Figure 10. Current v. PWM Arduino onboard. The developed LabVIEW interface being used as the command hub for the ROV, has integrated software power regulation. Pulse Width Modulation (PWM) is used in the LabVIEW interface in order to control the thrusters. PWM allows for the LabView software to send a signal down to the Arduino letting it know that the thrusters need to produce a certain amount of thrust based on the operators commands. The Arduino then sends a signal to the ESC, which allows for a certain amperage to be sent to the thruster. The amperage would vary based on the command from the operator, the higher the amperage the higher the thrust. In order to prevent any shorting, the maximum and minimum amounts of thrust were excluded off of the interface to avoid operating the thrusters at extreme conditions, thus keeping the entire ROV safer as lower amounts of current are allowed to travel through the ROV. 6. PROTOTYPE MANUFACTURING 6.1 Exoskeleton The first order of business when it came to the manufacture of the ROV was reviewing the technical drawings of the frame that were completed in the final proposed design of Chimaera. The drawings were used to take an inventory of the materials necessary to start the construction phase prior to any materials were ordered. A jigsaw was used to cut the Series 6 Aluminum and the ends were refined with a metal file. Once the sides were cut to specs (given a tolerance of a few centimeters), they had to be tapped for an 8 mm screw in order to be able to use the three-way corner brackets to join the cut extrusions to make the main frame, as shown in Figure 11. With the main frame of the Chimaera constructed, other primary components necessary to have a functioning ROV could be mounted. The brackets that held the horizontal thrusters in place were made of corner brackets that were donated to the team by Misumi USA, and the only modifications to the brackets were the four drilled holes that were used to bolt down the thrusters, as shown in Figure 12. The brackets that hold the vertical thrusters in place were manufactured from scrap metal and are additionally supported by L brackets to avoid and deflection of the main bracket. As discussed in previous sections, to diminish the effects of vibrations caused by the thrusters, crock pads were used as a damper between the mounting points of the brackets and thrusters, as well as, Figure 11. Tapping Aluminum Figure 12. Bare Frame lock-tight adhesive to make sure the screws and bolts would not come loose under operation. The main water tight canister that hold all the electrical components was mounted onto the frame using an acrylic mounting bracket that came along with the purchase of the canister. The acrylic bracket needed to be modified slightly to allow for aluminum L brackets to be used in order to secure the entire structure to the frame. Zip ties were also Proceedings of the 29th Florida Conference on Recent Advances in Robotics, FCRAR 2016, Miami, Florida, May 12-13,

6 Figure 13. Complete Exoskeleton the aluminum extrusion. used to secure the enclosure to the acrylic base that is placed on a support that is semicircular shaped within several slots provided in the acrylic base. Finally, the end effector was simply attached by inserting a nut and bolt into the slotted feature of 6.2 Internal Manufacturing The main challenge that came with wiring the ROV was the amount of cables that would need to go in and out of the water tight enclosure in order to make the 48 to 12 volt drop down. As mentioned above, six buck converters, which were placed at the bottom of the ROV were used to step down the voltage from 48 volts to 12 volts for each thruster. As well as a BEC that would drop down the voltage for the USB hub that supplied power to the camera and the two microcontrollers. The 48 Volt power supply would go into the water tight enclosure, the distribution board, and from there twelve cables would go out to to the buck converters. From the buck converters twelve more cables at 12 volts would go back into the water tight enclosure and connect to the six ESC (electronic speed controllers), controlling each thruster. This power conversion alone took most of the space available for wires going in and out of the water tight enclosure (Figure 14) since there were 14 openings maximum on the cap for the enclosure. The six cables from the thrusters also needed to enter the water tight enclosure and were connected to the other end of the ESC with the white wire connected to the yellow of the ESC, the green wire connected to the black wire of the ESC, and finally the blue wire of the thruster connected to the red wire of the ESC. The positive connection of the ESC to the thrusters, red and blue wires, were fused with a 15-amp fuse to avoid any of the equipment form getting damaged. The ESCs also had signal wires that were connected to the Arduino Mega in order to control each of the thrusters. Apart from the thrusters, the servos that were used to power the manipulator and all the sensors had to be wired inside the water tight enclosure. The Servo motors were powered by the Arduino Mega itself and the temperature sensor was also Figure 14. Wire Configuration (End Cap) Figure 15. Arduino Setup powered and connected to the Arduino Mega. The pressure sensor however, is connected to a separate Arduino Uno that is also powered by the USB hub and in turn powered by the BEC. The camera of the ROV is powered by the USB hub and transmits video back up top to the control center. One of the challenges in the wiring of the ROV was getting all the wires to fit inside the four-inch diameter enclosure. This took a lot of planning and careful positioning of all the components that needed to be inside the water tight enclosure. With all the cables that were coming in an Figure 16. Waterproofed End Cap out of the water tight enclosure it became very difficult to waterproof the cable penetrators, not to mention that a massive one-and-a-half-inch hole had to be made in the center of the end cap in order to fit all the cables that were needed. At first marine epoxy was used to seal the holes with the cables but water kept coming in through the small spaces between wires. To solve the problem, a hardening resin was used to fill the entire end cap to create a seal that would get into every crevice and hole possible. With the all the wiring done and the water tight enclosure sealed, the ROV was almost ready to throw in the water. The final step in the construction was to make the ROV neutrally buoyant using foam and air tight canisters., shows the completed and final version of the ROV that is ready to be tested in the water. 7. CONCLUSION The main task of the Chimaera build was to compete in the M.A.T.E. International Competition and the only way to do that, is to accomplish several tasks in the Florida Regionals event and video tape these tasks. The tasks include: 1) Maneuver under its own power 2) Complete the connecting the Environmental Sample Processor (ESP) to the power and communications hub product demonstration task. This task consists of: a. Retrieving the ESP s cable connector from the elevator or sea floor b. Laying the ESP s cable through at least one waypoint c. Opening the door to the port on the power and communications hub d. Inserting the cable connector into the port on the power and communications hub 3) Completes the task within 15 minutes 4) Follows all EXPLORER class power specifications With the final test of Chimaera conducted, all above tasks were completed and thus, Chimaera will be eligible to enter into the international competition. This task shows off the many features that Chimaera is capable of to include, maneuverability, proper waterproofing for safety, advanced circuitry for power conversion/regulation and a working manipulator arm. Even though new software needed to be learned for navigation of the ROV to be effective and several challenges were met in terms of signal interference, Logitech controller integration and developing a GUI, Chimaera was able to maneuver through waypoints and translate through an entire pool without trouble. Proceedings of the 29th Florida Conference on Recent Advances in Robotics, FCRAR 2016, Miami, Florida, May 12-13,

7 Figure 17. Final Prototype Likewise, with M.A.T.E. providing such a high voltage power supply, serious injury was in fact capable but many electric components were purchased to convert to lower voltage and safeguard other electronics via fuses. This project brings great credit upon the students involved and the professors that taught these students and instilled within them knowledge, as well as, values that will shape what type of engineers they will be in the future. All in all, with many moving parts to complete Chimaera, it is astonishing that the project timeline was met and several weeks of testing were completed prior to the competition so that any minor failures were fixed. 8. ACKNOWLEDGMENTS Our thanks are extended to the Robotics and Automation Laboratory located in the Department of Mechanical and Materials Engineering on FIU s Engineering Campus (EC) for allowing us to access the laboratory during the course of this work. The authors also acknowledge the partial funding provided by the Department of Mechanical and Materials Engineering towards the construction of the prototype. 9. REFERENCES [1] ROV, MATE. Explorer Class Competition Manual. Marine Advanced Technology Education, December 3, Proceedings of the 29th Florida Conference on Recent Advances in Robotics, FCRAR 2016, Miami, Florida, May 12-13,