For my last impossible object I built a Penrose triangle that was not symmetric (wit 2 strait sides and a twisted one). In this post I will try to build a symmetric object, using a few more techniques with Inventor.
- Getting the best visual result requires to tweak the geometry of the final object so my first step was to create 5 user parameters that will be used to build the triangle. I then proceed to build a sketch of one corner of the triangle. Only the left side was drawn (with 2 orthogonal constraints in red). The right side is only a symmetry relative to the Y axis.
- The second step is to extrude the profile on both side by thickness/2, then use the move body tool to rotate the result by “angleRotation” through the Y axis.
- Then use the circular pattern to create 3 copies of the corner. I had to use the “pattern a solid” option otherwise the default “pattern a feature” was copying the corner without the step 2 rotation.
- Create a loft can be created between the two side faces of the top and left corner, then this loft can be “circular patterned” to complete the triangle structure.
- The result needs to be smoothed on the junctions to make it less obvious. Select the 24 edges around with a 10mm radius fillet to finish the triangle.
The final shape result is more pleasing than my first attempt to build a penrose triangle. More parameters could help the getting a better final shape, but would increase the instruction complexity so I’ve chosen to keep it simple.