Straight Outta the portfolio again: Unnamed PVC ROV

0811081121In retrospect, I probably should have named this one. It started as a Sea Perch Project that MIT’s SeaGrant Lab gave me to keep me busy and entertained the summer of 2008, and quickly escalated into my Extended Essay for my high school’s IB program the next year. It was my first experience using a lathe and a mill (yes, I did shoot the chuck key into the ground) and other than the shafts I made for it, is entirely COTs parts. After I brought it home with me, I added on a camera, water bottles for adjustable ballast (instead of the buoys) some fishing sensors, a claw arm, and a water-sampler. It also is the second use of my “control” system that was seen in Steve-V1-Der and seemed to dominate my high school aversion-to-programming career.

IMGA0301I think that control scheme is small sticks for big thrusters and elevator, red buttons for panning thrusters, and black DPDT rockers for the arm.  This whole project was really important to me because it taught me a very important lesson I ended up using heavily in my Undergraduate Thesis: Waterproofing Things is Hard.

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I based most of my design off of the methods and plans laid out in Build Your Own Underwater Robot and Other Wet Projects by Harry Bohm and Vickie Jensen. Initially, I made the construction out of cemented PVC pipes and fittings, plastic rods, and small buoy floats, changing only the chassis design. Instead of going with their standard rectangular prism with non-parallel motors, I chose an upside-down pyramid with parallel motors. This allowed the ROV to descend much quicker than a previous design. I also ended up swapping out the foam buoys for empty water bottles, a far more readily available substitute. The bottles, while not looking quite as nice, allowed for adjustable buoyancy as well as greater overall buoyant force. In addition, I also changed the book’s recommended wax-potted motor for several modified and pre-waterproofed bilge pump motors with custom drive shafts and larger propellers.

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Other, more off-the-book modifications I made included adding in a few cheap off the shelf sensors, a remote fishing camera off of eBay, and a custom-made grabber arm. The off the shelf sensor was an inexpensive fishing tool designed to get both luminosity and temperature. The fishing camera came with its own monitor and displayed a laminated black and white picture. The arm was made of a long single piece of PVC tube filled with expansion foam, and was hinged on a waterproofed window motor allowing for easy articulation in the up and down direction. A simple waterproofed servo in an off-the-shelf grabber hand sat at the end of the arm and there were custom brackets with a test tube that could be attached to obtain water samples.

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The added power of the motors made a huge difference in the mobility of the ROV right off the bat. Additionally, the new shape of the ROV made descending much quicker at the cost of greatly-slowed rising speed. The sensor set worked perfectly at telling luminosity and temperature in the murky waters of the test lake, but the camera was of poor build quality, leaked, and broke. The actuators for the arm performed aptly, but it was difficult to use without a camera. The write-up for it in my Extended Essay received a passing grade nonetheless.

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