The 1950s were a golden age for the curious kid builder of all things balsa, plastic, Erector, and Lionel. Everything seemed to cost $1.90. I loved building models with my friend Merle down the street.
The Revell Company had the great line of Highway Pioneers plastic car models; you had to melt the axle with a hot knife to form a little blob of plastic that held the wheels on. Balsa wood airplane kits were common; some slipped together without glue and could be instantly tossed into the air, others had propellers you’d wind with a rubber band. There were wooden battleships with metal pins for cannons, decals, and other little details.
We had a soft spot for boats, since we lived a block from Lake Michigan. We made weird-looking boats from driftwood, which we’d pull along the shore with a long tree branch and string.
One day, Merle and I fished one of those free plastic submarines out of the bottom of a cereal box. Up and down it went in a small container of water with only a pinch of baking powder to create an air bubble for buoyancy. We loved it.
Fifty years later, I wondered if I could advance the design of that baking-powder sub and inject a little more fun by adding an electric motor. The answer is an unequivocal yes! Follow along as I share some model building ideas. You might learn some new skills along the way.
Sub Systems
The Kid Sub dives and ascends like the classic cereal-box toy subs, using baking powder to create bubbles for flotation. But unlike those toys, this one’s got forward propulsion from an electric motor, rudder, and dive planes, so it can perform powered dives, ascents, and turns, like a real submarine.
The circuit’s voltage is so low (1.5V) that immersing the switch and wires does not impair the sub’s function or present any danger. What does have to be waterproofed is the motor, which is sealed in petroleum jelly and beeswax.
Like a real submarine’s ballast tanks, the bubble chamber can contain water, making the sub negatively buoyant, or air, displacing the water and making the sub positively buoyant.
The powder tube contains the sub’s secret chemical mixture for vertical propulsion: ground-up Alka-Seltzer tablets.
The resulting air bubble forces water out of the bubble chamber, increasing the sub’s buoyancy.
The sub rises to the surface, relieving water pressure on the air release lever. The lever falls forward and unstops the hole in the bubble chamber, releasing the air bubble. Water rushes back into the bubble chamber, making the sub negatively buoyant. Submerged again, the air release lever is pressed back to its closed position by the water pressure caused by forward motion. Repeat.
Parts:
Soft drink bottles, plastic: NOS Energy Drink, 22oz (3) NOS has discontinued their blue bottles, but you can use any bottle that’s similar size with thick plastic walls, such as SoBe tea or elixir, 20oz (2)
Plastic knives (6) Dixie MEDIUM weight knives or with at least a 1/8″-wide spine at the back of the blade.
Propeller, one inch Dumas, (other small 1″ plastics boat propellers ok)
Motor, DC, 1.5V, 7/8″ diameter. Any motor will work as stock varies from these companies: American Science & Surplus sciplus.com or Electronicsurplus.com
Wire, insulated, 26 gauge, 2′ total length
Blue or Transparent RTV sealant, 1 tube available in auto parts stores
Cyanoacrylate (CA) glue aka super glue
Baking soda to accelerate the CA glue
Zap Goo flexible adhesive aka Zap-a-Dap-a-Goo
Epoxy, two-part such as J-B KwikWeld
Urethane foam, two-part expandable such as Silpak SP 328-4. Dow, Gap and Crack ( Great Stuff ) looks good too but I suggest anyone using any of these products experiment with them first to see what quantities to mix.
Mold release (Mothers) Carnuba car wax as a mold release for the urethane foam and found it works perfectly, However, be sure the inside of the mold has no edges and apply ample wax and let it dry sufficiently (to where it is dry to the touch) Silpak R-80 with a Preval Sprayer to apply it is an alternative.
Liquid styrene glue Testors Liquid Cement for Plastic Or the non-toxic version
Battery holder, 1×AAA McMaster Carr #7712K16
Square tube, brass, 1/8″, 0.014″ wall thickness, 12″ length K&S Engineering #151
Rod or wire, brass, 0.052″ diameter, 12″ length Detail Associates #2512 or similar
Rod, brass, With an ID to match your motor shaft’s OD
Acrylic tube, clear, 3/4″ OD × 5/8″ ID, 6 foot length cut to size McMaster Carr #8532K16
Hidden hinge Sonic Tronics #SOT130 Wholesaletrains.com
Machine screws, brass, 00-90×1/2″ (7) Walthers #947-1126
Hex nuts, brass, 00-90 (7) Walthers #947-1250
Battery, AAA
Switch, SPDT toggle, micro-subminiature Allied Electronics #G12AP
Plastic tubing, clear, ¾” OD × 5/8″ ID × 6″ length Grainger #4VXH9
Plastic tubing, acrylic, clear, 2½” OD, 0.65″–0.70″ wall thickness You only need about ½” total length.
Silicone rubber, two-part for moldmaking, such as Oomoo #25 or #30
Flexible tubing, 1/8″ OD, 1″ length such as aquarium air line, heat-shrink tubing, or covering from electrical wire
Corks, #5 (2) Fisher Scientific #07-781H or similar
Alka Seltzer tablets
Monofilament fishing line, 20yds
Coin, 25 cent or metal or plastic disc of the same size
Beeswax sold in hardware stores
Styrene sheet, 2″ x 1-½” × 0.030″ thick Plastruct #SSS-103
Petroleum jelly
Bolts, stainless steel, ¼-20: ½” (2), 1″ (1), with hex nuts (8) for ballast adjustments
Decals, self-adhesive, 1″ or 2″ letters such as Hy-Ko Products #MM series
EPDM sheet, about 3 × 3″ this is the same plastic used in blister packaging
Nylon plug, threaded, 3/8″
Test tube and cap, McMaster Carr #7012A44 and #6946A16
Corks, Size 6, McMaster Carr #9566K2
Sub-miniature toggle switch, Mouser Electronics # 633-G12AP
Tools:
Soldering iron and rosin-core solder
Hobby knife with new blades
Drill and small drill bits
Stepper drill bit for stern cap hole
Cup and pan to melt beeswax
Band saw or coping saw
Files, small
3/8″ × 18 NPT tap
