During the NASA International Space Apps Challenge, one of our goals was to build a water sampling device that could be attached to the payload bay on OpenROV. Water sampling is a very important capability for OpenROV to have in many situations because it allows researchers to bring water from the area they explored back to the surface where chemical, biological, and particulate analyses that may not have been possible in-situ can be done.
The way a water sampler works is quite simple- it allows water to flow into a chamber freely, then when a sample is to be taken, that chamber is closed so the water can't escape. This way, if a sample is taken it won't be contaminated from water at other depths as the sampler returns.
The concept we came up with was to have a tube which would be open at both ends mounted onto the payload bay with an extension spring running through the center of the tube which would pull to plugs together upon the release of a trigger.
Here are some of our initial sketches.
We went to the hardware store and picked up a few bouncy balls that would work as plugs and built a proof-of-concept model which seemed to work. When we cut the piece of fishing line holding the balls out of the tube, they pulled together to seal the tube.
We then developed a way to do the same thing with rubber stoppers (which would presumably make a better seal) and we built a mount that could be attached to the 50mm space of the payload bay rods. We also began considering some of the issues involving the triggering mechanism, namely that if a string were to be cut, the loose ends could get entangled in the props of the ROV. Our solution was to make a tensioner which would also function as a mechanism for giving compounding mechanical advantage at holding the plugs apart.
We were happy to find that the second version of the sampler also worked quite well and didn't seem to leak at all! After mounting the sampler to the payload adapter (we designed it to mount with zip ties so it could be easily removed and replaced with a fresh sampler during a mission), we patted ourselves on the back and moved on to the next challenge- designing the trigger mechanism. Any ideas?
*Special thanks to all the people at the Space Apps Challenge who helped us with the development of this awesome device!