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Réalisation - Solar boat 2

  • General building rules

  • Etape 1

    Leaving children freedom in their choice of design is important, but if some projects are clearly "on the wrong track" and surely won't work, it is important to help children to change their design. Avoid imposing the right solution, but try to bring children to analyse and rethink their project "by themselves". It is a good idea to ask them to first draw the plan of their boat before beginning the construction.

     

    Experience has shown that the following weak points are common:

     

    Bad balance Before fixing the different elements on the boat, it is important to check if the boat is balanced. Often the boats plunge forward or backward or lean on one side and the movement of boat is not straight. If the boat is already built you can slightly re-balance the boat with some weights (gluing nuts or washers, etc.) There is also a lot of designs that can easily topple. You can remedy this problem by adding a keel (e.g. by setting a large screw under the boat or by adding floats).

     

    Shape and weight of the boat For the boat to move easily forward, it's front should offer less resistance (pointed end). Round models or non-symmetrical perform generally poorly. Also check that the boat is not too big or heavy because the power of the engine is quite limited.

     

    Engine The motor can quickly rust if it is immersed in water. Ensure that it is not too close to the surface. Check, by exposing the cell to light, that it rotates in the right direction for the propeller to push forward. If this is not the case, invert the wires connected to the two polarities of the cell.

     

    Orientation of the solar cell Avoid a vertical orientation. An angle of 45 ° is a good choice if the solar cell is not fixed on a mobile system. You can build a support inclined at 45 ° to glue the cell on.



  • Specific building designs

  • Etape 2

    We give in the following steps a few design possibilities depending the types of propulsion. These proposals can be improved and adapted according to the needs.

  • Etape 3

    Propulsion by (marine) propeller

     

    Build a "bridge" with the galvanised fixing band, then secure the top motor with a plastic cable tie.

     



  • Etape 4

    Remove the metal connector from the plastic part of an electrical connector using a box cutter and a screwdriver.

     

    Using this piece of connection, connect the motor to a metal rod, and then add a propeller



  • Etape 5

    Push the "feet" of the bridge into the boat (made of expanded polystyrhène) so that the propeller is just below he water surface. Once the correct angle is found, it is possible to fix in place the "feet" of the bridge with hot glue

     

    Avertissement With this system, it is difficult to perfectly align the axis of the engine with the metal rod. There is inevitably a "whip" effect. To minimize it, try not to use too long rods and choose very straight ones. It is also possible to pass the rod through a hole at the back of the boat.

     



  • Etape 6

    Propulsion by wind propeller

     

    Build a "frame" using galvanised fixing band.

     

    At the top of this support attach the motor using a plastic cable tie.



  • Etape 7

    Attach the frame to the boat by passing a washer on a bolt, passing it from below through the hull made of expanded polystyrene (sagex).

     

    On the other side, place the frame over the bolt and fix with a washer and a nut.

     

    Add the propeller.



  • Etape 8

    Paddle wheel propulsion

     

    Avertissement Models of this type are more complex to build and require many settings to operate properly.

     

    Cut a small square of expanded polystirene (sagex) or rigid foam.

     

    Shorten the handles of 4 plastic teaspoons keeping 2 cm of the handles.

     

    Insert the spoons in the center of the 4 square sides.



  • Etape 9

    Create two hooks at the end of two iron rods. Pass the rods through the centre of the wheel both sides. The hooks prevent the wheel from turning independently from the axis.


  • Etape 10

    The same way than for the propellers, create 2 supports with galvanized fixing band. Fix the engine on one of them.

     

    Cut out a large rectangle from the back of the boat to leave a space of the wheel to turn in water.

     

    On each side of the hole fix the supports.

     

    Connect the paddle wheel to the axis of the motor with a electrical connector (see marine propeller) and pass the othe side of the axis through a hole in the support on other side of the hole.



  • Etape 11

    Avertissement As the photovoltaic cell and the motor are quite weak, it is important to check that the resistance of the water on the paddles is not too high. The paddles must enter the water with the back of the spoons, because otherwise the wheel would work like a turbine, scooping up water (which needs a lot energy). Set the height of the wheel so that the paddles enter just a little bit in the water. You shouldn't add tos many paddles.  3 or 4 are sufficient, because after the initial inertia a few light impulses are enough to keep the boat moving.

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