Buoyancy+Gravity wheel

[stupid]

This is my idea which I haven't tested yet. I have a feeling it won't work, I'm just too stupid to understand why not, maybe you can enlighten me.

The basic idea is that I am trying to make a buoyant wheel only have buoyancy on one side, thus (maybe)making it turn.

The blue disc is made out of a closed-cell foam. The black pac-man shaped object is the disc's housing. No water is allowed to enter the housing, even when the disc is spun underwater. The challenge here would be making a waterproof seal that was slippery enough so that the buoyancy could overcome the seal's grip on the disc. If this is a problem we can always make the disc bigger right? Maybe, I don't know.
Since the housing is filled with air, the right side of the disc is not affected by the water.

Thats really the best I can explain it.

[Rapadura]

I have another idea: Is there any object that, when is in one position, quickly sinks into water, and when is in another position floats into water surface?

What if this object naturally sinks to the bottom of a water tank, and when it reaches the bottom, its position is changed, and it starts to float, rising to the surface of the tank?

Could the energy used to change the position of the object be smaller than the energy generated by the movement of sinking and rising?

[Cloxxki]

I don't understand the OP's idea, but have learned that the very hardest part with buoyancy ideas is

to get the air bubble under water

Underwater is quite hostile towards inrushing air, it takes serious work to get a bubble down there.

Take a basic platic bag, watertight.
Hold it underwater at least 3 yards, no air in it. Now use a long straw to blow air under the bag. You'll notice just how much force is needed to get the air where you want it...

[mscoffman]

@stu 

You will need to think about the following.

o...You need to find the point that is the center of gravity of the disk
o...You need to find the point that is the center of gravity of the housing
o...You need to know that the above two, exchange forces at the axle
o...You need to repeat the process above for the center of bouncy
of the device.

Currently the center of bouncy and the center of gravity are very close
to each other...but they won't be after you decide what to do next.
Currently there are no reaction forces on the cover therefore it is less
than the force of friction of the seal so it will rotate around. What will
generally happen is that the cover will rotate until the center of gravity
and the center of bouncy come into opposition at vertical alignment.
The horizontal forces will cancel each and so the disk will not spin. Then
the device will change it's height in water so that the vertical forces
are canceled out as well. This is a problem with gravity powered machines
they will rotate only until forces come into balance. One needs to change
some balance to make them work...that requires energy.

:S:MarkSCoffman

[stupid]

Theres probably a few things I should add: The housing is stationary and does not move. Also the disc is connected to the housing with some kind of axle.