Ok,

I actually found the original article.  I am posting the text here.  The only image I made for this article is a black and white version of what I've already posted in this thread.

Here's the article.

This months article will be discussing duplication specifically applied to Carrara. The example of a bycicle wheel will be used.

A high level of detail for a specific piece can typically be achieved in two ways. One way is to include the detail in the texture or to hide or break up meshes using the transparency channel. An example would be a chain. It's possible to use a square tube and apply a shader to the tube in such a manner that it will look like a long string of chain links rather effectively. However, Some challenges may occur when the model is brought close up to the camera and rendered in a way that the texture becomes obvious.

The second method of adding detail can be to simply model it. This can be significantly cumbersome for many things but not when the detailed components are to be established in a repetitive pattern. Duplication becomes a very important capability.

The bycicle wheel shown in the image has many components which have been duplicated. The nubs on the tires and the spokes are all actual separate meshes stacked together into the pattern seen. The result is much more realistic than a texture and will stand up to rendering viewpoints which are close up.

Carrara has a neat method for duplicating lots of things over and over again. If the user performs one single duplication on a single object or group, the duplication can be repeated and all geometrical positions and scalings are ALSO duplicated again. This will continue until the user performs any kind of task other than duplication.

An example would be creating a line of boxes which are two units apart. The first box would be put into the scene. The box would be duplicated and moved two units in the positive X direction. When that second box is duplicated to create a third box, the third box will automatically be set two more units farther along the X direction. This will continue for as long as the user continues the duplication. It will end when the user performs any other task.

There's a trick that's good to know when duplicating components which have compound angles. The perfect example is the spokes in the wheel.

The original model of the spokes is a simple tube which makes the corner at the end for the loop around the center of the hub and the small expansion at the wheel rim. These spokes are tilted at a slight angle along the X axis so they will connect from the hub to the centerline of the wheel. If one single spoke were then duplicated and rotated along the Z axis into the new position, the spoke would have two rotational angles (compound). When the second spoke is duplicated, the resulting rotation will be goofed up and will not produce the proper result.

The way to fix this is to group the first spoke after it has been set in place the first time. It may seem odd to only have one object in a group but the result is a whole new frame of reference that can be rotated independently of the object inside the group. The hotpoint for the new group should be the center of the wheel hub. Rotating the grouped spoke along the Z axis only incurs one angle on the object. The grouped spoke can now be duplicated with the single rotation as many times as necessary with perfect results.

For the example presented, one corner (the first quarter) of the spokes were generated and then grouped again. The hotpoint for the new group was again placed at the center of the wheel hub and the quarter spokes group was rotated 90 degrees. Two more duplications later and all the spokes for one side of the wheel were completed.

All four corner groups were then grouped and the hotpoint was again set at the center of the wheel. This whole group was duplicated and rotated in the plane of the wheel (not the axis of the wheel) and the opposite side of spokes was generated.

The result is many many objects which are positioned and aligned perfectly producing excellent detail and a great render from any perspective.

The nubs on the wheel were generated in only a few minutes even though there are several hundred of them.

-Kix