submarine project?

Question

I need help with a school project for science. I need to create a model submarine that floats for 1 minute, sinks to the very bottom of the tank and then comes back up. It doesn't have to look nice, just work. It can not be directly pulled up or down

Answer 1

You can cause the sub to sink after a period of time by letting air slowly vent from a chamber. The vent hole could be made with a small diameter drill.

To surface the sub could drop ballast upon touching bottom leaving a small lead weight on the bottom.

Reserve bouyancy would then cause the sub to surface. If you made your sub out of pvc pipe the plastic alone might be slightly bouyant. You could increase this bouyance with a bit of foam. The weight would have to be heavy enough to overcome this reserve bouyancy.

All that is left is to have a sufficient lenght of pipe to trap a volume of air to keep it on the surface. The vent hole would have to be sized by experiment.

To drop the weight you could try:
1.) Relying on the downward momentium of the sub to dislodge it from a small hook
OR
2.) have a small stick which extends past the weight. The stick has a sliding mount so that when it is pushed in it will release the weight. The weight is mounted at an elevation somewhere between the end of the stick and the bouyant sub. This will allow the weight to pull the sub lower against the stick activating the release mechanism.

A variation of this system would be to have the stick trigger the opening of a sealed container which contains a dry alka seltzer. the water will react with the alka seltzer and blow ballast causing the sub to surface.

Check out the links on the water sampler. You may get an idea on how to trigger an action upon touching bottom. THe water samper uses a piece of surgical tubing to pull closed the end caps. The caps are held open by wire which is connected to a release mechanism. Think how you could have a piece of surgical tubing pull off a cp to a sealed bottle contailing the alka seltzer .

Also since you cannot directly pull the sub up could you use a line to drop a weight to the sub to trigger the release. See Nansen bottle link. You would not be directly pulling up th esub merely triggering the release. Kind of bending the rules but it may be allowed since its not expressly forbidden.

Answer 2

Ballast tank (coke bottle), with a weighted keel and a largeish row of holes in the tank next to the keel....

Make a small hole in the upper side of the tank such that after a minute sufficient water has entered thru the bottom to sink the thing (weight of keel will trim this).

Now, here is the sneaky bit, in the ballast tank is located some bicarbonate of soda and a small bottle with the opening near the top of the tank containing some hydrochloric or sulphuric acid..

The thing sinks and eventually as the water level in the tank rises, the water rises above the top of the acid bottle which causes the acid to mix with the water and reach the bicarbonate of soda, when this happens the reaction evolves CO2 (hopefully faster then the vent can exhaust it (which is why that hole is small), the gas pressure forces the water back out the large holes by the keel and the thing surfaces.

Dead simple and crude, but it should work.

If need be you could use a separate container of limestone chips and a mild acid to provide a minutes worth of gas to keep the thing afloat fully for the requisite time.

HTH.

Regards, Dan.

Answer 3

a container with enough ballast in it to make it neutral buoyancy

a small electric motor drives a fan (turbine) in a vertical tube
located in the middle

ballast could be the batteries

1. you attach wires and control it yourself tur on the fan
to drive it to the bottom . reverse the polarity and drive it to the top

2. Add a little electronics
a 555 timer and divider will give you a square wave output at one minute (high for one minute, low for the next....etc)

and a flip flop (divide by two) will drive the motor,- one side to the Q and the other to NOT Q or drive two transistors to do the same thing (depends on the size of the motor)


or if you are into chemistry you could miniaturize the whole thing just need a water based reaction that produces a gas
(pin holes let the thing sink.... the ingress of water sets off the reaction)