Oyster

Introduction

The oyster is a demonstration project for two things.

First, it shows an example of how to make more or less stiff structures out of hinges and plates (the pentagon, diamonds, squares, rectangles and triangles). When you take the red or the yellow shells out of the oyster they will simply keep their bent shape, even though each of the hinges actually hinges. Taken together the hinges and the plates can only assume one form. There is some slack in the hinges, which means that the shape is not super strong. However, it is strong enough for the second part of the demonstration.

The second thing that the oyster demonstrates is how, force can be transmitted through the hinges and the plates. Notice that the actuator only drives the yellow half of the oyster. When it pushes the yellow shell to a standing position, the yellow shell pushes down the black triangles in the base, which in turn push the red shell in upright position. It works the same as moveable origami figures (see for example https://www.youtube.com/watch?v=ThwuT3_AG6w ).

Inspiration for the oyster came from the design of a rhombicosidodecahedron, which is not available yet. I built only half of that one, and ‘discovered’ the basic oyster when I took it apart. See the video to the right. You can recognize the pentagons, squares and triangles from the rhombicosidodecahedron in the oyster. It might as well have become a venus fly trap or a baseball glove.

Notes on the design

If you don’t have the motor or the actuator, the demonstration still works! Just leave them out. Push down the pearl and the oyster will close. Let go and it will open. I never meant to make it work like, that but it does.

You may notice that the oyster does not close completely. I believe that is because the shells are not entirely stiff, neither are the triangles in the base and because there is a little slack in the hinges that connect the triangles to the shells. Notice also that the triangles in the base can change shape somewhat and that this has an effect on the shape of the shells and thus on how well they close.

The gear box has a slip wheel so that there is no problem when the oyster is fully closed or opened while the engine is still running. However, in spite of that, the actuator may get stuck and you may need to help it to reverse. The best is to switch off the engine, or put it in reverse, as soon as the oyster is fully closed or fully open.

Building instructions

You can download the .pdf here from bricksafe.com. It is for free and includes a list of all the parts that you need.

To put the oyster together, you may need to fumble a bit, but it can be done! If you like the puzzle, try out the 3D puzzle cube that I made based on the pearl.

It was not easy to model the shells in Stud.io because I don’t know the exact angles between all the plates. So, you will notice that in the manual, occasionally, the pins don’t exactly fill the pin holes. See for example in step 112, the hinges with the red ovals left and right.

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