Plastics

For the initial experiments, I used blown acrylic sheet and tubing to make the clam body. The shells were blown using a plastics blow oven, and the internal structures were blown using a heat gun. The seals were made of silicone, the bladder was made of latex, and the different structures were assembled with epoxy.

I used acrylic because it allows for a more direct process than prototyping with 3D printing. Ideas can be quickly tried out and modified with a bandsaw, sander, heat gun and hot knife, instead of working in a CAD file and printing new prototypes.

Electronics

The clam's circuit is composed of a bluetooth module, atmega, push-pull circuits, dc-dc converters, batteries and a wireless charger. A thermistor was used as a stand-in for other sensors, and data-logging was not implemented. This circuit was enough for the clam to control the solenoids and communicate data between the clam and a bluetooth device.

After breadboarding the circuit, I free-form soldered the electronics and gave it a conformal coating of epoxy. Like free-blowing plastic, free-form soldering is an intuitive and direct way to prototype. Different circuits can be easily explored, instead of going through the process of designing and fabricating new PCBs.

Bivalve

In my experimentation, I was able to work out the design of the shell, hinge, and adductor to form the bivalve. The hinge is formed by teeth, like an exaggerated version of the hinge teeth of natural clams. It has two fixed states (opened and closed) that are held in position by permanent magnets. The solenoid for the adductor is only used to change state.

In the closed state, the clam is sealed. In the open state, the clam has a gap to allow gas to release and water to flow in. Right now, that water inflow is what is used for sampling. It may be necessary to add a siphon to pump water into the clam for the sensors.

Bladder

I experimented with chemical reactions to fill the bladder. I did not want to use a pressure chamber to store the gas, because I did not want to build something to maintain those forces, or have a consumable component like a CO2 cartridge. I experimented with acetic acid and sodium bicarbonate (vinegar and baking soda), as well as hydrogen peroxide and catalase (from yeast), and both worked well. My only concerns are that the chemicals are nontoxic, do not affect the sensors, and are easy to clean and replenish.

Battery

The initial idea was for the clams to have copper on one shell and zinc on another to make a salt water battery. I scrapped that idea because the batteries I built lacked power, and an open battery could affect sensor measurements. I decided to use lithium batteries for now because they are powerful and can be recharged.

If a clam is lost and not recovered, then the lithium battery would be a pollutant, so a different battery would need to be used in the future if recoverability becomes a problem. A better salt water battery could be made that was more powerful and closed, so that it would not affect the sensors. In operation, when the clams are first seeded into the water, an opening in the battery would draw in salt water for use as an electrolyte. The opening would close and the clam would use that battery for it's data-logging mission. The batteries would not be able to be recharged electrically, but the clams could retain their wireless coils, and be powered wirelessly during data recovery. The salt water battery could be recharged for later missions by adding more elemental copper and zinc.

Now that the initial ideas have been explored, the design process will shift to working in CAD files for 3D printing and PCB fabrication.