The need for this ROV (Remotely Operated Vehicle) water sampler was thought up by my mother. She wanted something to make her water quality monitoring field work easier. The initial, and continuing, use for the sampler is measuring settleable solids and other qualities of river water. To execute environmental regulation, state law requires this measurement when there is construction on waterways in California. The measurement is sometimes specified for the middle of the river, at mid-depth. Taking water samples from the middle of the river without automation was a hassle, but with this ROV samples can be taken easily. Design constraints included the ability to self-propel to the middle of a river, perhaps 100 feet out; gather water from as much as 20 feet of depth; and return with a water sample of at least one liter.
Design
The catamaran structure is constructed of aluminum extruded angle. All mechanisms and components are mounted between two raised rails about 6 inches above the water, and two pool noodles are secured to the base of the catamaran for floatation. The overall dimensions of the catamaran are 4x2x1 feet.
Propulsion
The sampler uses a standard 18-pound (stationary thrust) trolling motor for thrust, which is vectored using a high-torque standard servo motor. The trolling motor is held by a quick-release shaft collar that allows the trolling motor to be held at different heights, down for use and up so the sampler can be laid flat on the ground when not in use.
Spool and Pump
The heart of the sampler is a spooled length of Tygon tubing. The spool is turned to lower the length of Tygon tubing to the sample depth and to bring the tube up again when it is time to return to the shore of the river. A dry-priming pump pulls water through the deployed tube, through a rotary joint and pushes it into a two-liter bottle that can be retrieved from the sampler.
Electronics
Power is provided by one 5AH, 12V sealed lead-acid battery that easily gives hour long runtimes at full throttle. Remote control is achieved through a standard hobby aircraft controller that includes a controller and a receiver. The receiver has six servo PWM signal outputs, four of which are used on the sampler. Three of the outputs send signal to electronic speed controllers I built myself, one of which is programmed to handle the feedback for Tygon tubing deployment, so there is no need for any central processing.
The sampler was first successfully used in the fall of 2015, and again in this summer of 2016. The sampler is light weight and has a hand grip, so it may be carried down a slope to a river by a single person without much difficulty. The sampler’s single-person usability is key, because it allows sampling to be safely performed by one person (so an individual need not venture out onto the water alone). While not designed for use with a tether, one can be attatched as insurance against any failure of the sampler. Fortunately, the tether has yet to come into play.
