AUV Design - Mechanical/Electrical Status Update (04/18/2012)
After multiple failed motor drivers, I finally convinced my teammates to allow me to use the proper wire schematic to connect the thruster-dedicated Arduino Uno to the motor drivers--a wiring scheme that I was taught and had used successfully on multiple occasions (including when testing one of the thursters several months earlier). I ordered three new L298 Dual H-Bridge motor drivers, cleanly/professionally soldered all of the components to them in the proper locations/orientations, developed three new colored, 6-wire, ribbon cables (i.e. cut-to-size, and soldered right-angle male pins to the ends so they could conveniently plug into the female sockets on the respective motor driver/Arduino Uno), and wired them properly (ensuring that the three paired timers on the PWM lines were in correspondence with the three thruster pairs). Ultimately, through all the presentations, reports, project, and other assignments, Hang and I were able to run successful air tests of both the thruster code and the mechanical subsystems code (with the newly-integrated marker dropper actuation). In addition to theorizing that one of the PWM pins (i.e. PWM5) on the original thruster-dedicated Arduino Uno was malfunctioning (verified by Hang using an oscilloscope), I also came up with the suggestion to have the mechanical subsystems code delay upon initialization such that upon conclusion of the thruster/general maneuverability code, it would actuate the solenoids and servo motor in sequence, thus actuating both of the torpedo launchers, the grasp/release mechanism, and the marker dropper. This method enabled us to avoid having to run one code, remove the AUV from the water, take off one of the end caps, switch the USB to the other Arduino Board, and then upload and run the second code--an inconvenient methodology.
Ultimately, the AUV successfully worked on Friday during our final hardware demo--the vehicle moved around at a sustained fully submerged depth, then launched the torpedoes about 6 feet (very slight modifications can be made if necessary to achieve even further distance and accuracy, including simply increasing the operation pressure to about 125 psi), actuated the grasp/release mechanism to both close (grasp), and then open (release), and the actuated the servo motor on the marker dropper mechanism to run through a sequence of rotations in order to successfully drop both of the markers upon command.
Photos/Video of the AUV at the ME Open House and at the FSU Morcom Aquatics Center final hardware demo (click on the link on the bottom left) can be seen in the photos/videos section of our website. Furthermore, the Final ME Presentation can be found in the documents section of the website as well:
http://www.eng.fsu.edu/me/senior_design/2012/team24/
A couple final mechanical features that were also made last week leading up to this demo were the manufacture and implementation of conductive plates (i.e. heat sinks) for the motor drivers, which screw directly into the back of the L298 chips and conduct directly to the top of the aluminum electronics platform (thus completing the conductive thermal network), stainless steel balancing plates, which are bolted to to the front of the bottom face of the AUV (on opposite sides of the camera enclosures) in order to neutralize the natural pitch angle to zero and increase the net density of the system slightly (to the desired design density), and the drilling of a pattern of relief holes in the cast acrylic torpedo cannons to enable rapid pressure equilibration, and thus drag reduction, during launch (this proved to be successful).
Currently, the vehicle is 100% mechanically complete, and the reproduced voltage regulator boards (my backup regulator was used during the hardware demo) should be re-integrated by the end of the week. Thus, the next phase of the AUV development will be the electrical/software integration of the IMU and pressure transducer, as well as installation of the right-angle USB cables and adapter in order to connect the Zotac to both Arduino Uno boards, as well as to the IMU and the two web cameras. This will enable codes to be uploaded directly to the Zotac--the central brain or heart of the AUV. Hang and Ryan will need to complete these tasks, and then successfully integrate/modify their mission control programs to enable the AUV to physically complete the replicated initial competition tasks. They will then need to derive programs for the "Kill Caesar" and "Gladiator Bins" tasks. I will attempt to develop PID control algorithms in order to maintain constant depths, velocities, rotate to desired relative angles, etc. over the summer--algorithms that would enable the experimental tuning of the PID gains (or at least PD gains).
If, and only if, these remaining tasks are completed I would be proponent of going to competition in San Diego, CA this July with a highly respectable product originating essentially from scratch, and from a first-year team. Only time will tell.
-Eric Sloan (ME Project Manager, Senior Design Team 4 - 15th Annual AUVSI Robosub Competition)
Wednesday, April 18, 2012
Wednesday, March 21, 2012
Progress Report - Mechanical and Electrical Design (03/22/2012)
Since my latest update, I have successfully completed both the voltage regulator board and the hydrophones interface PCB. The voltage regulator board contains three levels or stages. The board receives an input of about 32 V from the two lithium-ion batteries (in series), which gets stepped down to a regulated output of around 24.4 VDC. This voltage is supplied to each of the three L298 Dual H-Bridge motor drivers which operate the six thrusters. The output of this regulator (stage 1) also serves as the input to the stage 2 regulator, which reduces the 24.4 V down to about 19.1 V. The power cord for the Zotac board is soldered accordingly to pull this output voltage from the stage 2 regulator. This output voltage is similarly routed to the input of the stage 3 regulator which steps down the voltage to about 8.85 V in order to supply power to both of the Arduino boards. This voltage regulator board contains all the necessary input/output wires/cables as well so that it can directly connect to the kill switch Seacon connector, solenoid valve interface circuit, motor drivers, Arduino boards, Zotac PC, and also to the hydrophone interface PCB (the stage 3 voltage of about 8.85V can serve as the Vcc for the op-amps on the hydrophone interface PC-- 5V would be insufficient as the op-amps are not rail-to-rail input/output). The only negative of the board is that it features linear regulators instead of switching regulators for simplicity. However, I have derived a relatively simple, fast, effective way to conduct the dissipated heat from the voltage regulator chips to the aluminum platform, thus closing the circuit on a highly effective conductive network. This will effectively negate concerns of overheating and provide stable internal temperature during sustained operation.
I further designed and assembled the hydrophones interface PCB using DipTrace. The board came out nicely, and I spent several hours cleanly soldering all the op-amps, capacitors, resistors, wires, etc. to it. It too has all the necessary input/outputs connected to it, and is thus also directly ready for implementation/integration.
-Eric Sloan (Mechanical Engineering Project Manager - 15th Annual AUVSI Robosub Competition)
Since my latest update, I have successfully completed both the voltage regulator board and the hydrophones interface PCB. The voltage regulator board contains three levels or stages. The board receives an input of about 32 V from the two lithium-ion batteries (in series), which gets stepped down to a regulated output of around 24.4 VDC. This voltage is supplied to each of the three L298 Dual H-Bridge motor drivers which operate the six thrusters. The output of this regulator (stage 1) also serves as the input to the stage 2 regulator, which reduces the 24.4 V down to about 19.1 V. The power cord for the Zotac board is soldered accordingly to pull this output voltage from the stage 2 regulator. This output voltage is similarly routed to the input of the stage 3 regulator which steps down the voltage to about 8.85 V in order to supply power to both of the Arduino boards. This voltage regulator board contains all the necessary input/output wires/cables as well so that it can directly connect to the kill switch Seacon connector, solenoid valve interface circuit, motor drivers, Arduino boards, Zotac PC, and also to the hydrophone interface PCB (the stage 3 voltage of about 8.85V can serve as the Vcc for the op-amps on the hydrophone interface PC-- 5V would be insufficient as the op-amps are not rail-to-rail input/output). The only negative of the board is that it features linear regulators instead of switching regulators for simplicity. However, I have derived a relatively simple, fast, effective way to conduct the dissipated heat from the voltage regulator chips to the aluminum platform, thus closing the circuit on a highly effective conductive network. This will effectively negate concerns of overheating and provide stable internal temperature during sustained operation.
I further designed and assembled the hydrophones interface PCB using DipTrace. The board came out nicely, and I spent several hours cleanly soldering all the op-amps, capacitors, resistors, wires, etc. to it. It too has all the necessary input/outputs connected to it, and is thus also directly ready for implementation/integration.
-Eric Sloan (Mechanical Engineering Project Manager - 15th Annual AUVSI Robosub Competition)
Saturday, March 3, 2012
Progress Report - Mechanical/Electrical Design (03/03/2012)
The grasp/release mechanism, waterproofing of the marker dropper servo motor, implementation of a waterproof mission/kill switch, solenoid valve interface PCB, installation of several circuit boards in the electronics rack, and initiation of the replacement of our pressure transducer were successfully completed since my latest update.
The grasp/release mechanism was designed and mechanically simulated on Pro/Engineer - Mechansim. The design required the purchase of a shorter air cylinder with only 0.5" of actuated displacement (compared to the 2" displacement of the original single-acting air cylinder) in order to allow for the proper mechanical motion, grasping range, and size of the device. The device is essentially a mirrored 3-bar slider-crank mechanism, which uses press-fit bushings, as well as precision cut stainless steel dowel pins and e-clips in order to provide the necessary pin joints and motion constraints.
The servo motor for the marker dropper was waterproofed following extensive research and experiments on the two burned-out motors (one of which was inherited). Ultimately, a combination of Molykote silicone grease, high viscosity mineral oil, an o-ring, and DUCO cement were used, Silicone grease was liberally, yet cleanly added inside the gear shaft chamber where the output shaft exits the chamber, and where the input shafts enter the chamber. This chamber was then closed, and the back plate was removed to expose the electronics. I then poured the mineral oil into a container and rested the container at an angle in order to allow the oil ot accumulate toward the bottom, providing the necessary isolated depth of oil required for the next step. At this point, I completely submerged the servo motor (again, with the back plate removed and electronics exposed) in the mineral oil, and after allowing all the bubbles to escape, tightly closed up the back plate without ever allowing any part of the servo motor to surface. Once the servo motor had been successfully reassembled securely while submerged, I removed the motor from the mineral oil, carefully cleaned of the surfaces with soap and water, followed by some alcohol, and then applied DUCO cement to where the front plate connects to the body plate, and where the back plate connects to the body plate. This was to ensure no progressive leakage of water into the gear train chamber, or leakage of mineral oil out of the electronics chamber.Lastly, an o-ring was tightly pressed around the exposed tip of the output shaft, and the servo horn was torqued down tightly over this o-ring. The silicone grease around the o-ring was cleanly redistributed to form a clean, symmetrical barrier, and the electrical leads on the back of the servo motor were sealed at the base (i.e. where they exit the electronics chamber) using Plasti-Dip; this completed the process.
I completed the design of the solenoid valve PCB using DipTrace, making sure that no connection lines in the circuit intersected (thus required a multi-layer construction, of which the in-house milling facility was not capable) and submitted the Gerber files for in-house milling with specific requests to remove unnecessary copper on the top of the board, as well as around the holes on the bottom of the board. The result was a clean, compact, organized PCB to which I thereafter successfully soldered the components (i.e. resistors, NPN transistors, and wires that route to the leads from the SEACON connectors that route to the solenoid valves, ground, the output of the 9V regulator, and the corresponding I/O pins on the Arduino Uno board nearest this PCB on the electronics rack. Simple actuation of any of the four I/O (designated as output) pins opens the corresponding solenoid valve, and provided the air cylinder is set to output 100 psi, will launch one of the two torpedoes, close the grasp/release mechanism jaws, or open the grasp/release mechanism jaws (once closed).
I also assembled all the circuit boards (i.e. Zotac mini-itx, both Arduino boards, Phidget Spatial IMU, solenoid valve PCB, and the L298 Dual H-Bridge motor drivers) and organized them on the electronics rack so as to minimize unused space, provide sufficient room between boards to allow room for protruding wires, and ensure that the IMU would be located directly at the center/heart of the AUV. Furthermore, the goal was to designate as much space as possible for the final circuit board-- the amplification/filtering circuit for the hydrophones. Once this layout was established, I made final dimensions of the boards and hole locations, and recreated this layout on Pro/Engineer. Using the bottom left hole location as a local origin, and creating corresponding x- and y- axis through this point, I was able to chart the relative coordinates of all the other mounting hole locations. These coordinates were placed in Excel, and after securing the electronics rack on the mill and zeroing the drill to this local origin, I simply had to move the tooling plate to each of these coordinates and drill (the clearance holes were all the same). This provided an efficient, effective way to properly prepare the circuit boards for installation (using standoffs and screws).
I realized about a week ago the need for either an absolute or sealed-gauge pressure transducer since the reference vent cable was not anticipated and wouldn't have been able to be accomodated, so following a few phone calls and urgent emails, I was able to return ours and the company was willing to replace it with a sealed-gauge version. In addition, the company (Impress-Sensors Technology Ltd) was willing to send the version that directly output 0-5VDC, and which also had a marine bronze housing (even more corrosion resistant than the 316 stainless steel housing)--all for no additional cost. Sealed gauge was chosen over absolute because with absolute, the device outputs 0V in a vacuum. Thus, at atmospheric pressure, the device would have already output 2.5V, thereby significantly reducing the accuracy of the device for our application. The sealed gauge transducer, however, will output 0V at atmospheric pressure, and 5V at around 30 feet, making it almost ideal for our application. The sealed gauge uses 1atm as a reference, though, so if the atmospheric pressure at the testing site or competition site is slightly different, there would be very slight error introduced. This offset error, however, can be accommodated for by running a calibration test at each of these locations.
-Eric Sloan (ME Project Manager - 15th Annual AUVSI Robosub Competition)
The grasp/release mechanism, waterproofing of the marker dropper servo motor, implementation of a waterproof mission/kill switch, solenoid valve interface PCB, installation of several circuit boards in the electronics rack, and initiation of the replacement of our pressure transducer were successfully completed since my latest update.
The grasp/release mechanism was designed and mechanically simulated on Pro/Engineer - Mechansim. The design required the purchase of a shorter air cylinder with only 0.5" of actuated displacement (compared to the 2" displacement of the original single-acting air cylinder) in order to allow for the proper mechanical motion, grasping range, and size of the device. The device is essentially a mirrored 3-bar slider-crank mechanism, which uses press-fit bushings, as well as precision cut stainless steel dowel pins and e-clips in order to provide the necessary pin joints and motion constraints.
The servo motor for the marker dropper was waterproofed following extensive research and experiments on the two burned-out motors (one of which was inherited). Ultimately, a combination of Molykote silicone grease, high viscosity mineral oil, an o-ring, and DUCO cement were used, Silicone grease was liberally, yet cleanly added inside the gear shaft chamber where the output shaft exits the chamber, and where the input shafts enter the chamber. This chamber was then closed, and the back plate was removed to expose the electronics. I then poured the mineral oil into a container and rested the container at an angle in order to allow the oil ot accumulate toward the bottom, providing the necessary isolated depth of oil required for the next step. At this point, I completely submerged the servo motor (again, with the back plate removed and electronics exposed) in the mineral oil, and after allowing all the bubbles to escape, tightly closed up the back plate without ever allowing any part of the servo motor to surface. Once the servo motor had been successfully reassembled securely while submerged, I removed the motor from the mineral oil, carefully cleaned of the surfaces with soap and water, followed by some alcohol, and then applied DUCO cement to where the front plate connects to the body plate, and where the back plate connects to the body plate. This was to ensure no progressive leakage of water into the gear train chamber, or leakage of mineral oil out of the electronics chamber.Lastly, an o-ring was tightly pressed around the exposed tip of the output shaft, and the servo horn was torqued down tightly over this o-ring. The silicone grease around the o-ring was cleanly redistributed to form a clean, symmetrical barrier, and the electrical leads on the back of the servo motor were sealed at the base (i.e. where they exit the electronics chamber) using Plasti-Dip; this completed the process.
I completed the design of the solenoid valve PCB using DipTrace, making sure that no connection lines in the circuit intersected (thus required a multi-layer construction, of which the in-house milling facility was not capable) and submitted the Gerber files for in-house milling with specific requests to remove unnecessary copper on the top of the board, as well as around the holes on the bottom of the board. The result was a clean, compact, organized PCB to which I thereafter successfully soldered the components (i.e. resistors, NPN transistors, and wires that route to the leads from the SEACON connectors that route to the solenoid valves, ground, the output of the 9V regulator, and the corresponding I/O pins on the Arduino Uno board nearest this PCB on the electronics rack. Simple actuation of any of the four I/O (designated as output) pins opens the corresponding solenoid valve, and provided the air cylinder is set to output 100 psi, will launch one of the two torpedoes, close the grasp/release mechanism jaws, or open the grasp/release mechanism jaws (once closed).
I also assembled all the circuit boards (i.e. Zotac mini-itx, both Arduino boards, Phidget Spatial IMU, solenoid valve PCB, and the L298 Dual H-Bridge motor drivers) and organized them on the electronics rack so as to minimize unused space, provide sufficient room between boards to allow room for protruding wires, and ensure that the IMU would be located directly at the center/heart of the AUV. Furthermore, the goal was to designate as much space as possible for the final circuit board-- the amplification/filtering circuit for the hydrophones. Once this layout was established, I made final dimensions of the boards and hole locations, and recreated this layout on Pro/Engineer. Using the bottom left hole location as a local origin, and creating corresponding x- and y- axis through this point, I was able to chart the relative coordinates of all the other mounting hole locations. These coordinates were placed in Excel, and after securing the electronics rack on the mill and zeroing the drill to this local origin, I simply had to move the tooling plate to each of these coordinates and drill (the clearance holes were all the same). This provided an efficient, effective way to properly prepare the circuit boards for installation (using standoffs and screws).
I realized about a week ago the need for either an absolute or sealed-gauge pressure transducer since the reference vent cable was not anticipated and wouldn't have been able to be accomodated, so following a few phone calls and urgent emails, I was able to return ours and the company was willing to replace it with a sealed-gauge version. In addition, the company (Impress-Sensors Technology Ltd) was willing to send the version that directly output 0-5VDC, and which also had a marine bronze housing (even more corrosion resistant than the 316 stainless steel housing)--all for no additional cost. Sealed gauge was chosen over absolute because with absolute, the device outputs 0V in a vacuum. Thus, at atmospheric pressure, the device would have already output 2.5V, thereby significantly reducing the accuracy of the device for our application. The sealed gauge transducer, however, will output 0V at atmospheric pressure, and 5V at around 30 feet, making it almost ideal for our application. The sealed gauge uses 1atm as a reference, though, so if the atmospheric pressure at the testing site or competition site is slightly different, there would be very slight error introduced. This offset error, however, can be accommodated for by running a calibration test at each of these locations.
-Eric Sloan (ME Project Manager - 15th Annual AUVSI Robosub Competition)
Wednesday, February 22, 2012
Progress Report - Mechanical/Electrical Design (02/22/2012)
Since my most recent update, I have continued sedulous work on the AUV. I properly and securely installed all of the SEACON connectors to both the hull and camera enclosure end caps (adding silicone grease to each of the o-rings as well as the male plug connectors, and applying Loctite thread sealant to the middle threads of the female socket connectors), completed the construction of the camera enclosures (and successfully installed the forward facing camera in the top enclosure), designed and manufactured the grasp/release mechanism, waterproofed the "waterproof" (hobby servos like the one carried over from last year's team are not rated for sustained submersion of up to 16 ft--not even close) servo motor (Traxxas 2056), designed, manufactured, and installed the kill switch mount and kill switch (features a military grade rubber boot (IP86* rating--sustained submersion)), installed the newly arrived pressure transducer, developed a design for the amplification/filtering PCB for the hydrophones, and designed and manufactured the solenoid valve interface PCB using a program called Dip Trace which I downloaded and then learned via a tutorial and introductory documentation in a day.
The grasp release mechanism design consists essentially of mirrored 3-bar (or 4-bar in a liberally general sense) slider crank mechanism. I briefly consulted Dr. Hollis (Mechanical Systems II and Modeling and Simulation Professor) in regards to a couple of the design details (e.g. the use of bushings over bearings, lubrication suggestions, etc.) as well as an approach to deriving the motion profile of the proposed linkage system. I ended up reviewing my Mechanical Systems I text book (I keep all my engineering and advanced mathematics books) and found a set of equations that could be directly applied to this model. It was during these calculations when I realized that the current design wouldn't output the intended range of motion of the jaws, and in fact would have induced significant stress build-up due to not physically being able to move in such a way in order to allow the single-acting air cylinder to translate the full 2" during actuation. I then set up a sketch on Pro/E, allowing me to make immediate design modifications by providing an efficient means of adjusting various design parameters (link lengths (i.e. distance between pivots) and claw shapes). Ultimately, I concluded that it was best to get a new ($18) single-acting air cylinder that has 0.5" of travel (it looks the same as the other single-acting air cylinder, but is about 2" shorter as well). This modification, along with the redesigned jaws provided the desired motion of the grasp/release mechanism, and without hindering the ability of the single-acting air cylinder to extend to its full capacity. The design features 8.5" of grasping range (closing to a very slight out-of-plane overlap), a custom piston adapter, and a fixed pivot (achieved via minor additions to the frame, as well as another custom adapter piece). Furthermore, it uses bushings, 1/4" - stainless steel dowel pins, e-clips, and shaft shims.
I successfully tested the newly acquired Traxxas 2056 servo motor a few days ago as well, serving as final confirming evidence that the other two servo motors were, in fact, burned out as suspected. After extensive research on servo motor waterproofing methods, materials were ordered, and test were performed on these dead servos. The conclusion was to apply silicone grease to the output shaft of the gear train, submerge and assemble the servo in a high-viscosity mineral oil bath, ensure the screws were tightly fastened (the screws already had o-rings on them), clean the shell using alcohol, apply Duco Cement along the two interfaces of the servo shell (as insurance), add an lubricated (silicone grease) o-ring around the output shaft (externally), and then tightly screw the servo horn onto the output shaft. Finally, Plasti-Dip was used where the wires protrude from the back of the servo motor in order to ensure a definitive water tight seal.
The kill switch issue was the other waterproof task that was on my mind. The original source provided an astronomical quote that even earned complaints from their most recent customers--the Bellagio and the Navy. It was decided that it was far more economical (and necessary) to attempt to custom waterproof the toggle switch that was inherited from last year's team. Rough ideas were thrown around, including the implementation of a balloon around the toggle switch to prevent water while not restricting actuation. The general concept was decent, but I wasn't too fond of the sophomoric technique that was being implied. Thus, I conducted more extensive research and discovered an established company that manufactures silicone boots that are directly compatible with a vast array of toggle, push button, etc. switches. An appropriate boot for the toggle switch was obtained and this, combined with the addition of Plasti-Dip to the leads of the switch, should provide a reliable water tight seal. Furthermore, it has been decided to use this comfortable-actuation switch not only as our kill switch, but also as our mission start switch--preventing the need for an additional switch, and thus additional threaded hole in the rear end cap for the complementary set of SEACON connectors. The switch is conveniently mounted on the top of the back face of the AUV--directly behind the compressed air tank, and out of the way of thrusters or any mechanical subsystem.
I also discovered, installed, and briefly learned a PCB design program called Dip Trace. I was able to derive the solenoid valve interface PCB (containing four identical circuits in a compact arrangement) which has dimensions of 3.35" x 1.45", and also has built-in mounting holes. The transistors, resistors, solenoid valve wires, and protection/snubber/flyback diodes will simply need to be soldered to this board. Lastly, I sat down with Antony on Friday and confirmed my initial determination that we in fact need 25 dB of amplification in the pre-amplifier for the hydrophones. I have derived circuit design with the aid of National Semiconductor's Webench, which will consist of of four identical circuits containing a third-order active band-pass filter connected to two gain stages (i.e. two-stage amplifier using op-amps). The active filter should sufficiently filter out noise from the delicate hydrophones, and the amplifier should provide the necessary gain in signal so that as the AUV enters into its pinger detection state (following completion of the Kill Caesar mission), the signal amplitude should be about 0.4 V, and as the AUV approaches about 1.5 m, the signal strength should be about 4.5 V. Since these signals will be sent to A/D converters for eventual digital signal processing, it was critical to design the circuit so that the signal would not saturate the A/D converters within the desired range from the target pinger. I will construct this complex and robust circuit using Dip Trace as well. However, due to the severe magnitude of this particular PCB, I will likely end up sending the file off to a company (possibly National Semiconductor) to construct the custom PCB using more advanced milling equipment than is currently available at the FAMU - FSU College of Engineering.
*We are also currently pursuing further funding from the college, and also are in the process of submitting/have submitted the competition entry fee, and requested the lending of a transponder (pinger) from the competition staff (they have items that teams can borrow for up to four weeks, including IMUs, PCs, pingers, hydrophones, etc.).
I will update my blog again at the start of spring break. Until then, I will be continuing the progress of the AUV until the task is done, we go to competition, and we win the competition.
-Eric Sloan (Mechanical Engineering Project Manager - 15th Annual AUVSI Robosub Competition)
Since my most recent update, I have continued sedulous work on the AUV. I properly and securely installed all of the SEACON connectors to both the hull and camera enclosure end caps (adding silicone grease to each of the o-rings as well as the male plug connectors, and applying Loctite thread sealant to the middle threads of the female socket connectors), completed the construction of the camera enclosures (and successfully installed the forward facing camera in the top enclosure), designed and manufactured the grasp/release mechanism, waterproofed the "waterproof" (hobby servos like the one carried over from last year's team are not rated for sustained submersion of up to 16 ft--not even close) servo motor (Traxxas 2056), designed, manufactured, and installed the kill switch mount and kill switch (features a military grade rubber boot (IP86* rating--sustained submersion)), installed the newly arrived pressure transducer, developed a design for the amplification/filtering PCB for the hydrophones, and designed and manufactured the solenoid valve interface PCB using a program called Dip Trace which I downloaded and then learned via a tutorial and introductory documentation in a day.
The grasp release mechanism design consists essentially of mirrored 3-bar (or 4-bar in a liberally general sense) slider crank mechanism. I briefly consulted Dr. Hollis (Mechanical Systems II and Modeling and Simulation Professor) in regards to a couple of the design details (e.g. the use of bushings over bearings, lubrication suggestions, etc.) as well as an approach to deriving the motion profile of the proposed linkage system. I ended up reviewing my Mechanical Systems I text book (I keep all my engineering and advanced mathematics books) and found a set of equations that could be directly applied to this model. It was during these calculations when I realized that the current design wouldn't output the intended range of motion of the jaws, and in fact would have induced significant stress build-up due to not physically being able to move in such a way in order to allow the single-acting air cylinder to translate the full 2" during actuation. I then set up a sketch on Pro/E, allowing me to make immediate design modifications by providing an efficient means of adjusting various design parameters (link lengths (i.e. distance between pivots) and claw shapes). Ultimately, I concluded that it was best to get a new ($18) single-acting air cylinder that has 0.5" of travel (it looks the same as the other single-acting air cylinder, but is about 2" shorter as well). This modification, along with the redesigned jaws provided the desired motion of the grasp/release mechanism, and without hindering the ability of the single-acting air cylinder to extend to its full capacity. The design features 8.5" of grasping range (closing to a very slight out-of-plane overlap), a custom piston adapter, and a fixed pivot (achieved via minor additions to the frame, as well as another custom adapter piece). Furthermore, it uses bushings, 1/4" - stainless steel dowel pins, e-clips, and shaft shims.
I successfully tested the newly acquired Traxxas 2056 servo motor a few days ago as well, serving as final confirming evidence that the other two servo motors were, in fact, burned out as suspected. After extensive research on servo motor waterproofing methods, materials were ordered, and test were performed on these dead servos. The conclusion was to apply silicone grease to the output shaft of the gear train, submerge and assemble the servo in a high-viscosity mineral oil bath, ensure the screws were tightly fastened (the screws already had o-rings on them), clean the shell using alcohol, apply Duco Cement along the two interfaces of the servo shell (as insurance), add an lubricated (silicone grease) o-ring around the output shaft (externally), and then tightly screw the servo horn onto the output shaft. Finally, Plasti-Dip was used where the wires protrude from the back of the servo motor in order to ensure a definitive water tight seal.
The kill switch issue was the other waterproof task that was on my mind. The original source provided an astronomical quote that even earned complaints from their most recent customers--the Bellagio and the Navy. It was decided that it was far more economical (and necessary) to attempt to custom waterproof the toggle switch that was inherited from last year's team. Rough ideas were thrown around, including the implementation of a balloon around the toggle switch to prevent water while not restricting actuation. The general concept was decent, but I wasn't too fond of the sophomoric technique that was being implied. Thus, I conducted more extensive research and discovered an established company that manufactures silicone boots that are directly compatible with a vast array of toggle, push button, etc. switches. An appropriate boot for the toggle switch was obtained and this, combined with the addition of Plasti-Dip to the leads of the switch, should provide a reliable water tight seal. Furthermore, it has been decided to use this comfortable-actuation switch not only as our kill switch, but also as our mission start switch--preventing the need for an additional switch, and thus additional threaded hole in the rear end cap for the complementary set of SEACON connectors. The switch is conveniently mounted on the top of the back face of the AUV--directly behind the compressed air tank, and out of the way of thrusters or any mechanical subsystem.
I also discovered, installed, and briefly learned a PCB design program called Dip Trace. I was able to derive the solenoid valve interface PCB (containing four identical circuits in a compact arrangement) which has dimensions of 3.35" x 1.45", and also has built-in mounting holes. The transistors, resistors, solenoid valve wires, and protection/snubber/flyback diodes will simply need to be soldered to this board. Lastly, I sat down with Antony on Friday and confirmed my initial determination that we in fact need 25 dB of amplification in the pre-amplifier for the hydrophones. I have derived circuit design with the aid of National Semiconductor's Webench, which will consist of of four identical circuits containing a third-order active band-pass filter connected to two gain stages (i.e. two-stage amplifier using op-amps). The active filter should sufficiently filter out noise from the delicate hydrophones, and the amplifier should provide the necessary gain in signal so that as the AUV enters into its pinger detection state (following completion of the Kill Caesar mission), the signal amplitude should be about 0.4 V, and as the AUV approaches about 1.5 m, the signal strength should be about 4.5 V. Since these signals will be sent to A/D converters for eventual digital signal processing, it was critical to design the circuit so that the signal would not saturate the A/D converters within the desired range from the target pinger. I will construct this complex and robust circuit using Dip Trace as well. However, due to the severe magnitude of this particular PCB, I will likely end up sending the file off to a company (possibly National Semiconductor) to construct the custom PCB using more advanced milling equipment than is currently available at the FAMU - FSU College of Engineering.
*We are also currently pursuing further funding from the college, and also are in the process of submitting/have submitted the competition entry fee, and requested the lending of a transponder (pinger) from the competition staff (they have items that teams can borrow for up to four weeks, including IMUs, PCs, pingers, hydrophones, etc.).
I will update my blog again at the start of spring break. Until then, I will be continuing the progress of the AUV until the task is done, we go to competition, and we win the competition.
-Eric Sloan (Mechanical Engineering Project Manager - 15th Annual AUVSI Robosub Competition)
Saturday, February 11, 2012
Progress Report - Mechanical Design (02/12/2012)
Since my latest blog post, the AUV has continued to progress significantly. The compressed air tank, tank/high-pressure regulator, and secondary/low-pressure regulator were successfully installed their simple, elegant Delrin mount. The tank was filled to capacity (i.e. 3,000 psi) at a local scuba diving shop named Coral Reef, and successfully integrated with the network of nylon gas distribution tubes. Furthermore, the single-acting air cylinder for the grasp/release mechanism was successfully installed on its recently designed and manufactured mount. The simple, efficient angle-bracket mount was intelligently designed for its efficient use of material, relative ease of manufacture, and with dimensions that enable the jaws of the grasp/release mechanism to successfully pick up the rescue object (i.e. laurel wreath) without the bottom camera enclosure interfering. The single-acting air cylinder, as well as the torpedo launchers (with the redesigned (embedded neodymium magnets in place of the appended low-pull bar magnets), low friction, proper density, properly balanced torpedoes) were successfully tested in air.
An aluminum heat dissipation platform and the electronics rack were also successfully redesigned and manufactured. This redesign was prompted by the recent decision to use the Zotac mini-itx board in place of the Beagleboard-xM as the main control unit due to the need for greater processing power (particularly for the computer vision algorithms). The new heat dissipation platform was designed and manufactured to slide snugly into the hull end cap slots, and also to provide a wider region in the center (between the two lithium-ion batteries) on which to mount the new 6.7" x 6.7" Zotac PC. The revised electronics rack features one level which spans the majority of the interior hull, and essentially forms a bridge over the batteries and Zotac PC. This electronics rack not only features an efficient use of material and an aesthetic appeal, but also provides much easier access to the circuit boards than in the previous multi-level design. Furthermore, the redesigned electronics rack uses the same amount of material as the original design, and also is very cleanly welded at the joints (in place of cumbersome, interfering nuts, bolts, and angle brackets) to provide a strong, durable, elegant result.
The SEACON connectors also arrived, so I carefully drilled and tapped (using a mill tool plate attachment that operates in polar coordinates) each of the aluminum end caps to enable the installation of the female bulk head connectors. In addition, I cut the wires of each of the peripheral subsystems to about 3", and then measured and cut each of the corresponding male SEACON cables to length in order to ensure the reduction of excess cable (and thus weight). Each of the cables was then stripped to prepare them for soldering, heat shrink, and Plasti-Dip on Monday. The male cables for the SBT150 thrusters were also soldered to the leads of the thrusters inside the back end caps, and the cable was then potted using a waterproof epoxy. Plast-Dip will also be brushed over the external epoxy in order to provide a slightly cleaner look, as well as another layer of protection against water leakage.
The new acrylic camera enclosure boxes also arrived and were carefully mounted to their redesigned supporting platforms. I conducted exact measurements of these enclosures in order to ensure that their respective fixed end caps will fit firmly and securely, reducing the potential for leakage following the addition of the 100% silicone caulking around the four outer edges. The redesigned mounts for the cameras were also successfully installed (in the center of each of the enclosures (and the vehicle)) recently. I discovered a product called Duco Cement which was proved to be a fantastic find. It is a completely clear, very strong adhesive that dries within about 15 minutes. It has been used to adhere the camera enclosures to their respective aluminum base plates, as well as to adhere both of the camera enclosure mounts to the inside surface of the acrylic enclosures, and to adhere the polycarbonate pressure transducer supports to the center line of the top of the acrylic hull.
By the end of this upcoming week, I expect to have the redesigned fixed end caps for the camera enclosures manufactured and installed, all the male cables successfully connected to their respective peripheral subsystems (including the pressure transducer, which should arrive by Friday, but excluding the kill switch and the servo motor of the marker dropper (both will be ordered Monday)), the electronics rack successfully installed inside the hull with holes drilled in line with the circuit board mounting holes, the thrusters re-installed on the vehicle, the files required to make the solenoid valve PCBs obtained and submitted, the grasp/release mechanism jaws water cut, and the pre-amplifier circuit for the hydrophones tested on a breadboard. The kill switch (which will now be mounted to the frame on the back of the vehicle behind the compressed air tank), new servo motor, and new SEACON connectors (for the kill switch and to enable code to be uploaded to the main control unit without having to repeatedly open the end caps) will also be ordered on Monday, and should arrive the following week.
The vehicle is still on pace for mechanical and electrical completion by spring break (i.e. March 5th), but there is considerable work to do until that point in order to reach this goal. Currently my main concern is interference in the signal from the hydrophones, and the successful design and integration of the custom pre-amplifiers for the hydrophones. I will be drawing on my Mechatronics II knowledge, experience, and resources in order to make this a success as well. Also, once the vehicle is successfully completed and refined in preparation for underwater mission testing in March and April, I will direct my attention to helping Hang Zhang develop control algorithms for the thrusters using information from the IMU and pressure transducer as input sensory information.
Lastly, the vehicle was recently weighed, and is on pace for a projected 87 lb. Due to the 84 lb threshold, we might lose a few points (110 lb is the max weight in order to qualify to compete). This is not of major concern as this was both anticipated, and has a relatively small impact in reference to the entire mission. Furthermore, there is a potential that either (a) the weight limit will be increased slightly, or (b) this projected weight ends up being a slight overestimate.
I will provide another update on the status of the AUV in the coming weeks.
-Eric Sloan (ME Project Manager, 15th Annual AUVSI Robosub Competition)
Since my latest blog post, the AUV has continued to progress significantly. The compressed air tank, tank/high-pressure regulator, and secondary/low-pressure regulator were successfully installed their simple, elegant Delrin mount. The tank was filled to capacity (i.e. 3,000 psi) at a local scuba diving shop named Coral Reef, and successfully integrated with the network of nylon gas distribution tubes. Furthermore, the single-acting air cylinder for the grasp/release mechanism was successfully installed on its recently designed and manufactured mount. The simple, efficient angle-bracket mount was intelligently designed for its efficient use of material, relative ease of manufacture, and with dimensions that enable the jaws of the grasp/release mechanism to successfully pick up the rescue object (i.e. laurel wreath) without the bottom camera enclosure interfering. The single-acting air cylinder, as well as the torpedo launchers (with the redesigned (embedded neodymium magnets in place of the appended low-pull bar magnets), low friction, proper density, properly balanced torpedoes) were successfully tested in air.
An aluminum heat dissipation platform and the electronics rack were also successfully redesigned and manufactured. This redesign was prompted by the recent decision to use the Zotac mini-itx board in place of the Beagleboard-xM as the main control unit due to the need for greater processing power (particularly for the computer vision algorithms). The new heat dissipation platform was designed and manufactured to slide snugly into the hull end cap slots, and also to provide a wider region in the center (between the two lithium-ion batteries) on which to mount the new 6.7" x 6.7" Zotac PC. The revised electronics rack features one level which spans the majority of the interior hull, and essentially forms a bridge over the batteries and Zotac PC. This electronics rack not only features an efficient use of material and an aesthetic appeal, but also provides much easier access to the circuit boards than in the previous multi-level design. Furthermore, the redesigned electronics rack uses the same amount of material as the original design, and also is very cleanly welded at the joints (in place of cumbersome, interfering nuts, bolts, and angle brackets) to provide a strong, durable, elegant result.
The SEACON connectors also arrived, so I carefully drilled and tapped (using a mill tool plate attachment that operates in polar coordinates) each of the aluminum end caps to enable the installation of the female bulk head connectors. In addition, I cut the wires of each of the peripheral subsystems to about 3", and then measured and cut each of the corresponding male SEACON cables to length in order to ensure the reduction of excess cable (and thus weight). Each of the cables was then stripped to prepare them for soldering, heat shrink, and Plasti-Dip on Monday. The male cables for the SBT150 thrusters were also soldered to the leads of the thrusters inside the back end caps, and the cable was then potted using a waterproof epoxy. Plast-Dip will also be brushed over the external epoxy in order to provide a slightly cleaner look, as well as another layer of protection against water leakage.
The new acrylic camera enclosure boxes also arrived and were carefully mounted to their redesigned supporting platforms. I conducted exact measurements of these enclosures in order to ensure that their respective fixed end caps will fit firmly and securely, reducing the potential for leakage following the addition of the 100% silicone caulking around the four outer edges. The redesigned mounts for the cameras were also successfully installed (in the center of each of the enclosures (and the vehicle)) recently. I discovered a product called Duco Cement which was proved to be a fantastic find. It is a completely clear, very strong adhesive that dries within about 15 minutes. It has been used to adhere the camera enclosures to their respective aluminum base plates, as well as to adhere both of the camera enclosure mounts to the inside surface of the acrylic enclosures, and to adhere the polycarbonate pressure transducer supports to the center line of the top of the acrylic hull.
By the end of this upcoming week, I expect to have the redesigned fixed end caps for the camera enclosures manufactured and installed, all the male cables successfully connected to their respective peripheral subsystems (including the pressure transducer, which should arrive by Friday, but excluding the kill switch and the servo motor of the marker dropper (both will be ordered Monday)), the electronics rack successfully installed inside the hull with holes drilled in line with the circuit board mounting holes, the thrusters re-installed on the vehicle, the files required to make the solenoid valve PCBs obtained and submitted, the grasp/release mechanism jaws water cut, and the pre-amplifier circuit for the hydrophones tested on a breadboard. The kill switch (which will now be mounted to the frame on the back of the vehicle behind the compressed air tank), new servo motor, and new SEACON connectors (for the kill switch and to enable code to be uploaded to the main control unit without having to repeatedly open the end caps) will also be ordered on Monday, and should arrive the following week.
The vehicle is still on pace for mechanical and electrical completion by spring break (i.e. March 5th), but there is considerable work to do until that point in order to reach this goal. Currently my main concern is interference in the signal from the hydrophones, and the successful design and integration of the custom pre-amplifiers for the hydrophones. I will be drawing on my Mechatronics II knowledge, experience, and resources in order to make this a success as well. Also, once the vehicle is successfully completed and refined in preparation for underwater mission testing in March and April, I will direct my attention to helping Hang Zhang develop control algorithms for the thrusters using information from the IMU and pressure transducer as input sensory information.
Lastly, the vehicle was recently weighed, and is on pace for a projected 87 lb. Due to the 84 lb threshold, we might lose a few points (110 lb is the max weight in order to qualify to compete). This is not of major concern as this was both anticipated, and has a relatively small impact in reference to the entire mission. Furthermore, there is a potential that either (a) the weight limit will be increased slightly, or (b) this projected weight ends up being a slight overestimate.
I will provide another update on the status of the AUV in the coming weeks.
-Eric Sloan (ME Project Manager, 15th Annual AUVSI Robosub Competition)
Tuesday, January 24, 2012
Progress Report - Mechanical Design (01/24/2012)
The development of the vehicle has continued to progress. After several hours of research and speaking with salespeople from a couple suppliers of paintball tanks, regulators, etc., it was determined that compressed air should be used instead of CO2 for several reasons:
(1) The outlet pressure of CO2 is a strong function of the operating temperature, and is thus difficult to predict/regulate. In fact, paintball CO2 tanks don't come with a regulator, while all paintball compressed air tanks come with a regulator already installed as a standard. Apparently the ability to regulate compressed air much better than CO2 is the reason why higher-quality paintball guns and more experienced paintball players use compressed air instead of CO2.
(2) Originally it was thought that CO2 tanks would be far more compact than compressed air tanks, however, this is not necessarily the case. There are compressed air tanks that are just as compact as compressed CO2 tanks (as I have found by shopping online). This discovery eliminates the issue of dimensional constraints.
(3) After a few phone calls, I was able speak to a supplier in northern California who had a very versatile selection of regulators, adapters, etc. In fact, they had a low-pressure regulator that can be directly attached to the tank regulator, and that also has the exact desired threaded outlet (i.e. 1/8" FNPT), thus culminating in a compact, efficient, reliable completion to the gas distribution circuit.
*Note: The compressed air tank (with the tank regulator) and the low pressure regulator (both the tank regulator and the low-pressure regulator (required to drop the pressure down from about 850 psi to 100 psi) have analog gauges installed on them) have been ordered and will arrive shortly.
Furthermore, I developed an efficient design for the compressed air tank mount, which will be machined using the lathe and drill press tomorrow morning (relatively easy to manufacture, and the stock has already been selected).
In addition, a mounting plate for the pressure transducer has been water cut, and I picked up the one-way check valves from Grainger and successfully installed/tested them on the exhaust outlets of the two torpedo launcher air cylinders, as well as on the outlet of the exit solenoid valve for the grasp/release mechanism.
Tomorrow afternoon (when the McMaster-Carr order arrives), I will carry out my improvised modification to the camera enclosures and perform another water tight test (hopefully my strategy will work--I am optimistic as it seems like a good approach). This strategy involves adhering 3/8" thick EPDM rubber (i.e. the same material used for the gaskets) to the bottom surface of the top camera enclosure, and the top surface of the bottom camera enclosure, allowing the neoprene sealing washers, bolts, and threaded rod to pass through clearance holes. The EPDM rubber will be adhered to the aforementioned surfaces using the gasket adhesive (very strong). Thereafter, I will cleanly apply caulking around the four edges of the exposed surface of each of the two rubber pads. Then, I will pour epoxy into each of the six total exposed holes. This should prevent any leakage through the bolt threads, sealing washers, etc., as was the issue earlier. Furthermore, an appropriate tape (specifically for smooth surfaces such as acrylic) was purchased in a recent order. This tape will be placed along the outer edges of the enclosures in a clean fashion such that all the caulked edges will have this extra layer of protection. The final outcome should hopefully be more reliable (i.e. water tight), aesthetically-appealing camera enclosures.
I also made another (hopefully final) McMaster-Carr order this evening, which includes an assortment of items such as another NPT adapter, a liquid rubber wire-protecting agent, heat shrink tubing (with an internal adhesive to assist in preventing water from coming into contact with the soldered wires), a 5/16" thick sheet of acrylic (to be used for the hydrophones mount, as well as to complete the pressure transducer mount), and a few small neodymium magnets which I hope to use on the revised versions of the torpedoes which were 3D printed late this afternoon, and will be retrieved tomorrow morning for surgery (i.e. I need to drill into and install a stainless steel rod at a specific depth--similar to the initial version). The small neodymium magnets were chosen for their compactness due to their high magnetic field/volume ratio, and should provide an even cleaner design than with the bar magnets. Also, this slight revision is being done because I forgot to factor in the addition of the magnet when performing my calculations, and thus the center of buoyancy deviated from the original center of mass, thus yielding torpedoes that tilted back slightly when submerged underwater. This negatively affected their hydrodynamics, and after removing the magnet from one of the torpedoes, the density was perfect, the center of mass and buoyancy were great, and the torpedo moved nicely through the water. The necessary adjustments are being made to the second generation of torpedoes.
I also discovered on Monday that the SEACON connectors will arrive in the first week of February as the order was unfortunately not completely processed until January 6th (despite being submitted prior to winter break). This is okay, though, as there are still other productive tasks that can be completed until then. In addition, the pressure transducer will be ordered on Friday (W-9 forms were not supplied by the company, so the order had to be cancelled, and it will need to instead be ordered out of pocket), and two more SQ26 hydrophones will be purchased by the end of the week (the two from last year were determined to work fine for the frequency range required, and I spoke to branch of the company in Seattle, where I was provided a quote and also made aware of the availability of these hydrophones.
Furthermore, the solenoid valves were successfully tested today, and my proposed circuit will work. I will have Hang help me make a PCB containing four of these identical circuits shortly.
-Eric Sloan (ME Project Manager - AUVSI Robosub Competition)
The development of the vehicle has continued to progress. After several hours of research and speaking with salespeople from a couple suppliers of paintball tanks, regulators, etc., it was determined that compressed air should be used instead of CO2 for several reasons:
(1) The outlet pressure of CO2 is a strong function of the operating temperature, and is thus difficult to predict/regulate. In fact, paintball CO2 tanks don't come with a regulator, while all paintball compressed air tanks come with a regulator already installed as a standard. Apparently the ability to regulate compressed air much better than CO2 is the reason why higher-quality paintball guns and more experienced paintball players use compressed air instead of CO2.
(2) Originally it was thought that CO2 tanks would be far more compact than compressed air tanks, however, this is not necessarily the case. There are compressed air tanks that are just as compact as compressed CO2 tanks (as I have found by shopping online). This discovery eliminates the issue of dimensional constraints.
(3) After a few phone calls, I was able speak to a supplier in northern California who had a very versatile selection of regulators, adapters, etc. In fact, they had a low-pressure regulator that can be directly attached to the tank regulator, and that also has the exact desired threaded outlet (i.e. 1/8" FNPT), thus culminating in a compact, efficient, reliable completion to the gas distribution circuit.
*Note: The compressed air tank (with the tank regulator) and the low pressure regulator (both the tank regulator and the low-pressure regulator (required to drop the pressure down from about 850 psi to 100 psi) have analog gauges installed on them) have been ordered and will arrive shortly.
Furthermore, I developed an efficient design for the compressed air tank mount, which will be machined using the lathe and drill press tomorrow morning (relatively easy to manufacture, and the stock has already been selected).
In addition, a mounting plate for the pressure transducer has been water cut, and I picked up the one-way check valves from Grainger and successfully installed/tested them on the exhaust outlets of the two torpedo launcher air cylinders, as well as on the outlet of the exit solenoid valve for the grasp/release mechanism.
Tomorrow afternoon (when the McMaster-Carr order arrives), I will carry out my improvised modification to the camera enclosures and perform another water tight test (hopefully my strategy will work--I am optimistic as it seems like a good approach). This strategy involves adhering 3/8" thick EPDM rubber (i.e. the same material used for the gaskets) to the bottom surface of the top camera enclosure, and the top surface of the bottom camera enclosure, allowing the neoprene sealing washers, bolts, and threaded rod to pass through clearance holes. The EPDM rubber will be adhered to the aforementioned surfaces using the gasket adhesive (very strong). Thereafter, I will cleanly apply caulking around the four edges of the exposed surface of each of the two rubber pads. Then, I will pour epoxy into each of the six total exposed holes. This should prevent any leakage through the bolt threads, sealing washers, etc., as was the issue earlier. Furthermore, an appropriate tape (specifically for smooth surfaces such as acrylic) was purchased in a recent order. This tape will be placed along the outer edges of the enclosures in a clean fashion such that all the caulked edges will have this extra layer of protection. The final outcome should hopefully be more reliable (i.e. water tight), aesthetically-appealing camera enclosures.
I also made another (hopefully final) McMaster-Carr order this evening, which includes an assortment of items such as another NPT adapter, a liquid rubber wire-protecting agent, heat shrink tubing (with an internal adhesive to assist in preventing water from coming into contact with the soldered wires), a 5/16" thick sheet of acrylic (to be used for the hydrophones mount, as well as to complete the pressure transducer mount), and a few small neodymium magnets which I hope to use on the revised versions of the torpedoes which were 3D printed late this afternoon, and will be retrieved tomorrow morning for surgery (i.e. I need to drill into and install a stainless steel rod at a specific depth--similar to the initial version). The small neodymium magnets were chosen for their compactness due to their high magnetic field/volume ratio, and should provide an even cleaner design than with the bar magnets. Also, this slight revision is being done because I forgot to factor in the addition of the magnet when performing my calculations, and thus the center of buoyancy deviated from the original center of mass, thus yielding torpedoes that tilted back slightly when submerged underwater. This negatively affected their hydrodynamics, and after removing the magnet from one of the torpedoes, the density was perfect, the center of mass and buoyancy were great, and the torpedo moved nicely through the water. The necessary adjustments are being made to the second generation of torpedoes.
I also discovered on Monday that the SEACON connectors will arrive in the first week of February as the order was unfortunately not completely processed until January 6th (despite being submitted prior to winter break). This is okay, though, as there are still other productive tasks that can be completed until then. In addition, the pressure transducer will be ordered on Friday (W-9 forms were not supplied by the company, so the order had to be cancelled, and it will need to instead be ordered out of pocket), and two more SQ26 hydrophones will be purchased by the end of the week (the two from last year were determined to work fine for the frequency range required, and I spoke to branch of the company in Seattle, where I was provided a quote and also made aware of the availability of these hydrophones.
Furthermore, the solenoid valves were successfully tested today, and my proposed circuit will work. I will have Hang help me make a PCB containing four of these identical circuits shortly.
-Eric Sloan (ME Project Manager - AUVSI Robosub Competition)
Wednesday, January 18, 2012
Progress Report - Mechanical Design (01/18/2012)
The vehicle will undergo a watertight test this afternoon. If there is any leakage in the hull or any of the two camera enclosures, more silicone caulking will be added. Hopefully this will not be necessary, however, so that we can hand the enclosures over to Ryan for testing with the web cameras inside. Also, new mounting plates were made for the bottom thruster and the marker dropper mechanism. The heads of the screws for the bottom acrylic supports were intersecting into the locations of the clearance holes in the original thruster mounting plate. The mounting holes were simply migrated inward toward the center in the new mounting plate--a simple adjustment. For the marker dropper mounting bracket, I simply cut an aluminum angle bracket to 1" x 1" x 3.75" dimensions, drilled a few holes, and attached it to the marker dropper and frame. Furthermore, I designed individual identical mounting plates for each of the four solenoid valves. I decided on revised locations to mount the solenoid valves, as well as the four-way split adapter for the gas lines. The new scheme will be very efficient (i.e. more direct), aesthetically appealing, and also distributes the mass of these valves symmetrically throughout the vehicle, thus maintaining proper balance. I also ordered a CO2 tank, a lightweight pressure regulator, and a check valve (if it works properly, I will purchase two more). So, the CO2 distribution system should be ready for testing toward the end of this week. Once the screws and T-slot nuts arrive (this evening), the solenoid valves will be mounted to their corresponding plates, the plates will be attached to the 80/20 frame, and I will start connecting the nylon gas lines (tubing) to the push-to-connect adapters. During this stage, I will also cut the tubing to size so that there won't be excess tubing hanging off the vehicle. When the CO2 tank and pressure regulator arrive, the network can be completed and preliminary tests can ensue. Thereafter, I will make interface circuits (low side drive BJT) to enable easy actuation of the solenoid valves with a micro controller. These tests will likely be done with a Dragon Board due to familiarity. The SEACON connectors should arrive shortly as well. Once they arrive, they will be installed in the inner end caps of both the hull and camera enclosures. The four SBT150 thrusters can then be potted using epoxy, and the leads of all the thrusters can be carefully soldered to the corresponding leads of the male cables. The interface will be protected using shrink wrap at a minimum.
-Eric Sloan (ME Project Manager - AUVSI Robosub Competition)
The vehicle will undergo a watertight test this afternoon. If there is any leakage in the hull or any of the two camera enclosures, more silicone caulking will be added. Hopefully this will not be necessary, however, so that we can hand the enclosures over to Ryan for testing with the web cameras inside. Also, new mounting plates were made for the bottom thruster and the marker dropper mechanism. The heads of the screws for the bottom acrylic supports were intersecting into the locations of the clearance holes in the original thruster mounting plate. The mounting holes were simply migrated inward toward the center in the new mounting plate--a simple adjustment. For the marker dropper mounting bracket, I simply cut an aluminum angle bracket to 1" x 1" x 3.75" dimensions, drilled a few holes, and attached it to the marker dropper and frame. Furthermore, I designed individual identical mounting plates for each of the four solenoid valves. I decided on revised locations to mount the solenoid valves, as well as the four-way split adapter for the gas lines. The new scheme will be very efficient (i.e. more direct), aesthetically appealing, and also distributes the mass of these valves symmetrically throughout the vehicle, thus maintaining proper balance. I also ordered a CO2 tank, a lightweight pressure regulator, and a check valve (if it works properly, I will purchase two more). So, the CO2 distribution system should be ready for testing toward the end of this week. Once the screws and T-slot nuts arrive (this evening), the solenoid valves will be mounted to their corresponding plates, the plates will be attached to the 80/20 frame, and I will start connecting the nylon gas lines (tubing) to the push-to-connect adapters. During this stage, I will also cut the tubing to size so that there won't be excess tubing hanging off the vehicle. When the CO2 tank and pressure regulator arrive, the network can be completed and preliminary tests can ensue. Thereafter, I will make interface circuits (low side drive BJT) to enable easy actuation of the solenoid valves with a micro controller. These tests will likely be done with a Dragon Board due to familiarity. The SEACON connectors should arrive shortly as well. Once they arrive, they will be installed in the inner end caps of both the hull and camera enclosures. The four SBT150 thrusters can then be potted using epoxy, and the leads of all the thrusters can be carefully soldered to the corresponding leads of the male cables. The interface will be protected using shrink wrap at a minimum.
-Eric Sloan (ME Project Manager - AUVSI Robosub Competition)
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