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How to create a helix in Modeller?

The cross-section of the helix should be modelled first.  In the example shown here, a circular cross-section has been created using four arcs in the XZ plane.

If the helix is to be solid then the cross-section should be made into a surface (as shown above) otherwise the helix will be hollow.  The lines forming the cross-section surface should then be meshed with the required number of null divisions so that when copied and swept later these divisions will also be copied.

The cross-section should then be rotationally swept by 90 degrees about the centre of the helix to form one quarter of a toroid as shown.  The rotation transformation used to sweep the cross-section should be saved for later use.

The pitch of the helix, a, is the vertical distance travelled when one complete revolution of the helix has been made.  The newly created surface forming the opposite end of the helix must now be translated by a distance a/4 in the vertical direction (Z in the example shown) and the mid-points translated by a/8 in the same direction.  The a/4 translation transformation should be saved for later use.

The lines running between the two ends of the model should now be meshed with an appropriate null dataset.

One quarter of one rotation of the helix has now been created and all that remains is to copy this (n x 4) times using the saved transformations where n is the number of helix pitches required.  This is carried out by selecting the complete quarter model and using the copy command with the Compound option.  Both saved transformation datasets are used in the compound copy.

In this example n is equal to 5 and therefore the quarter model was copied 20 times.

The helix can then be meshed with 3D solid continuum elements for a solid helix or 3D shells for a hollow helix.


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