this is a submarine that can be built from items in your recycling bin and a single weekend. it dives to a certain depth (depending on how you adjust it) and comes back up after a certain amount of time.
two large bottles and three small bottles
plastic tubing (straws work fine too)
dowels or sticks
*you can also use baking soda and vinigar instead of baking powder and water **sand may also be needed
Step 1: The Ballast Tank
start by cutting the top off a large bottle. then cut a large piece of flat plastic (no edges) from the plastic bag so you have a sheet of flexible plastic. fold it in half and glue to make a pouch that can just hold the large topless bottle. put the bag inside the bottle through the top and glue the edge of the bottle to the edge of the pouch. then cut a small hole for air to pass through and inflate the ballast tank to make it float to the surface when in use.
Step 2: The Timer
the submarine uses a water clock to time how long before dropping its cargo and coming back up. you can rig a clock to do this, but the water clock is easier. first, take the other large water bottle and cut out the top. only take out the bottom. if you take off too much nothing will fit. mine barely did. take one bottlecap and punch a hole in the bottom. glue the bottom (with the hole) onto the top of another bottlecap with a hole in the bottom. glue the whole assembly on the inside with the bottle horizontal and the caps vertical near the bottom of the bottle and cut a hole above the place that the top cap was glued. the caps can be filled with water with an eyedropper or a funnel throught the hole. fill all gaps with hot glue. take a small bottle and cut so it fits in the bottle and stick it in with modelling clay so it covers the caps glued in earlier and make sure it has room to fall.
Step 3: The Inflater
the inflater inflates the ballast by increasing internal pressure to decrease density. first, cut off the top and bottom from one of the small bottles. tape or hot glue them together and make sure the seam is waterproof. hot glue a bottlecap onto the end of a short dowel and glue the other end of the dowel to a longer dowel at 90 degrees. fill the bottle with A.water B.vinigar and fill the bottlecap with A. baking powder B. baking soda.
Step 4: Connecting the Parts
take the timer drip pan (the bottle bottom) out and glue it to the inflater dowel. put everything back in and glue in place. cut a hole anywhere near the center of the bottle and attach a short length of tubing. cut a similar hole in the ballast and connect with a length of plastic tubing.
Step 5: The Finishing Touches
to stabilize the craft, add a ballast made from a water bottle filled with sand and attached to the rest of the sub with dowels. to lauch the sub, fill all containers with the required liquid and drop it in any deep body of water. if it floats, then add more sand. if it sinks and won't come back up, take off some sand. of course, if it sinks and won't come up you will have to abandon it unless you tie string to the top to retreive it.