Mechanical ribcage having variable number of ribs and derived heights

Question

How do you create ribs that shrink in height along the inside of a track?

Here is a screen shot showing the problem:

With the array and mirror settings hidden, you can see a quarter rib:

The ribs do not decrease in height, which causes them to extend beyond the track:

I'd like to limit the height of each rib such that it connects to the support beam, shown selected here:

How can this be accomplished without modeling each rib individually (i.e., using curves, empties, constraints, arrays, and so on)?

Answer 1

Method 1: even rib size

You can use a combination of some modifiers such as:

• Array (using object offset pointing to an empty to get the step distance to increase; notice that the empty doesn't have the same Y coordinate of the object origin, so each step the repeated object gets nearer to the center)
• Boolean (to cut away the parts that exceed the middle line with a "control" box)
• Mirror (to repeat the other half)

Method 2: slightly deformed ribs

Use a regular X-axis Array modifier (much simpler to set up than the array previusly presented) and deform the result with a lattice with two control points only in order for each direction (U,V,W) to get a linear deformation:

While the second method is probably faster, the first would give you more control and precision.