DIY Underwater Video Camera

This underwater camera is made by housing a small security camera inside a pressure tight container. This setup will work perfectly in clear water, but with increased water turbidity, lights will be necessary to improve performance. Construction details for the lights and housing are shown below.

This plumbing accessory form a local DIY store forms the main part of the housing. It was chosen for its compact size, and it allows both ends to be easily removed so the components remain accessible.

The two end caps are not fully closed. This allows a small perspex window to be added for the camera to see through. A perspex disc should be cut to fit neatly inside the cap with an o-ring either side. PTFE tape wrapped around the screw thread will ensure a tight fit when screwing on the caps.

The cable is sealed in the middle of another perspex disc. This allows the ends to be unscrewed without twisting the cable. Layers of Polymorph and epoxy resin are built up either side of the disc, and around the cable to form a strong flexible seal.

The light source is an array of bright LED’s. The LED’s shown here are from surplus parts and are not the most effective light source for a camera. The best LEDs would be either white or infra red, as the camera will respond best to these. The LEDs and resistors were mounted on a plastic strip which is formed into a ring to fit over the end of the camera housing. They are sealed using Polymorph and epoxy resin.

The lights shown here are a combination of blue, ultra violet, white, and infra red LEDs. There are fifteen in total. It looks pretty cool, but a white or IR light would be better. The power for the LED’s was taken from the same 12V battery used for the camera so it was neccesary to reduce this power to a lower level for them. To do this a power pulse modulator was used with the frequency set high and the pulse width set very low. This served as a dimming module for the LEDs so the brightness could be finely contolled.

Check out he video captured with this camera in the Alsager Mere section.

This is a battery powered motor for a small rowing boat. The motor used is from an electric wheelchair which ran from 24V. The motor has a built in reduction gearbox to provide a large torque to the wheels on the wheelchair. This gearing ratio was far to high for the propeller. The prop needs to turn much faster in order to generate the right amount of thrust to move the boat.

Fortunately the motor used had a small part of the main rotor protruding from the opposite end to the gearbox which was sufficient to attach a sprocket. This sprocket was linked with a chain to another sprocket on the main axle. This axle was then connected to a 90 degree 2:1 gearbox from a cheap angle grinder which was then attached to the propeller.

The propeller is from an old barge and is a little larger than necessary, but the motor provides just enough power to compensate.

The control system uses a pulse width modulation system for a smooth speed control and efficiency. The circuit used is based on the power pulse modulator but with the high voltage MOSFET being replaced by an array of lower voltage high current bipolar transistors so that the huge currents demanded by the motor could be tolerated.

The other switches on the control box are for forward/stop/reverse and to choose between 12V and 24V operation. These are simply large power switches that are used to directly switch the power as necessary.

A Homemade Magnetohydrodynamic Thruster (MHDT)

Based on the image on the left, it is possible to make a simple MHD thruster, just powerful enough to propel a toy boat.

This type of thruster generates magnetic fields by passing an electric current through a liquid conductor, such as sea water. Using another magnetic field, the liquid can be pushed in a chosen direction, therefore generating thrust. You can easily make one of these devices from household materials and a couple of neodymium magnets. In the diagram below the small arrows represent the intersecting electric and magnetic fields. the large blue arrow represents the flow of water.

Two opposing inner faces of a rectangular plastic tube are covered by metal strips. These are the main electrodes and should have a connection for a battery. Magnets are attached on the outside of the tube so that they are attracting each other, and are at 90° to the electrodes.

The metal strips here are cut from a thin Aluminium sheet, but you can just use foil although it wont last as long. The electrolysis and salt water corrosion soon eats away at the metal, but foil should last just long enough to see it working. The best sort of electrode would possibly be made from carbon. A good power source for this device would be a pulse width modulated supply such as our power pulse modulator. This would allow you to adjust the frequency and width of electical pulses so that you could get the optimum thrust from your design.

To learn how a MagnetoHydroDynamic thruster works, see the Propulsion section.

This setup shows the electrodes closer together than the magnets. The combination of magnets used in this device were not strong enough to move the electrified water with any decent force. At only 1.5V in salty water, large amounts of electrolysis occurs, but the water does generally flow in one direction.

The key to getting the best performance it to have the strongest magnetic field you can get across the gap between the electrodes.

Also make sure the magnets are behind the plastic or insulated somehow. You don’t want them shorting out the electric current in the water.

The valveless pulse jet engine or pulse detonation engine is the most simple type of jet and is therefore popular among hobbyists as a DIY project. it is often referred to as a ‘tuned pipe’ because its operation depends upon making the parts the right size and shape so that it fires, or resonates at the engines natural, fundamental frequency. This type of jet propulsion does not need any type of turbine, turbofan, or propeller, making it much less complex than a typical turbojet. In a turbojet the turbine or turbofan is used to compress the fuel/air mixture in the combustion chamber so that it is more efficient and powerful.

This jet engine has absolutely no moving parts and it relies on the simple shape of the combustion chamber and exhaust for it to function. The fuel to the jet is provided at a constant rate, but it is detonated in pulses. After each explosion there remains a lower pressure area inside the combustion chamber. This is immediately filled as air rushes back in and mixes with the fuel feed ready for detonation again.

This example of a homemade jet engine is about as simple as it gets, but it could not be used for propulsion purposes because it is only safe to operate for a short time. The main body of the pulse jet engine is made from copper pipes and various adaptors. The combustion chamber is made from two copper adaptors that have been cut and soldered together. Copper is an excellent thermal conductor which helps to spread the heat throughout the jet, but solder melts very easily so if the jet engine were allowed to run for more than a few seconds this part could come apart. This was enough to demonstrate the principles of operation which is all this DIY jet engine was designed for. If you wanted a working model for providing thrust, it would be necessary to consider different materials as a running jet will get very hot.

These images show the basic ‘tuned pipe’ without the spark plug and gas supply. Tuning was achieved by altering the length and width of the parts used. This was quite simple as there are wide range of plumbing parts that will easily fit together.

The fuel was provided from a cheap blow torch and was injected into the combustion chamber using fine brass tubes bought from a local hobby shop. This chamber also contained a tiny homemade spark plug. The spark rate could be controlled by varying the power to a HV capacitor connected in parallel with the spark plug.

The power supply for the tiny spark plug was made from a mini cold cathode PSU connected to a HV diode and capacitor. An alternative is to use an ignition coil and an ignition coil driver circuit.

The spark plug its self was just a single wire inside a small glass fuse. This wire was connected to one capacitor terminal (live) and the body of the jet engine was connected to the other terminal (earth). The spark would jump from the tip of the wire to the inside of the combustion chamber to ignite the fuel mixture.

The simple design and adjustability of this jet means that a wide variety of fuels can be used. The most common fuel used is kerosene and propane, but common lighter gas will work for this basic demonstration. Click here for More information on Jet Engines.