DIY Baking Powder Diving Spud-Marine

Hi there! I love making fun things ever since I was a kid. When I grew up, I was fortunate to become a professional toy designer at Mattel, then an independent toy inventor. Here's my easy, DIY project that uses the science of baking powder with the good old spud to create a fun toy for kids of all ages!

Step 1

First, cut a potato into a ¾" diameter cylinder, about 3" long. Or just use a small fingerling potato about that size. Use a piece of ¼" brass tubing as a plug cutter. Press the tube all the way into the potato to make 3 through-holes along its length. This will reduce the mass of the potato for better diving.

Step 2:

Enlarge the bottom of the center hole to make a flared conical opening. This will create an air chamber for the bubbles. Next, make a periscope. Cut a thin piece of wood about ½" by 1" and drill a ¼" hole in the center. Cut a 1" long piece of a ¼" wood dowel and insert it in the hole.

Step 3:

Place the periscope into the middle hole in the potato.

Time to test! Place the Spud-marine into a tall pitcher or vase of water. If it floats, cut off some of the periscope and try again. If it sinks FAST, trim off some of the potato and try again. If it sinks very s..l..o..w..l..y, it’s ready! The sub should be just ever-so slightly heavier than neutral buoyancy for best diving action.

Step 4:

Remove the sub and shake it dry. Pack some baking powder (not baking soda!) into the bottom of the center hole. Use some more wood dowel to tamp it in tightly.

Gently lower the sub back into the water and let it sink, then watch as it bubbles, rises, breaches the surface, burp its bubbles, and then sink again! How many times will your sub rise and sink before you have to reload the powder?