### Demo 2 – another sample on robustness

Let’s switch off Cheetah solver and load file *Demo2_Ac.dwg* from the folder *Demo 2 – Car*.

You get the sample car model:

Now, being in the standard AutoCAD mode, let’s try to drag some points of this model. As you can see, dragging a little practically any point of the model results in dramatic destruction of the whole model:

This is non-robust behavior – a small drag of the point, marked by the red arrow on the image above, caused dramatic and unpredictable changes of some lines of the model.

You can try to drag some other point (see red arrow in the image below) and get similar destructive behavior of AutoCAD solver:

Now let’s switch on *Cheetah mode* – the AutoCAD constraints will be converted into Cheetah constraints:

In Cheetah mode, the behavior of this model is radically different. You can drag any point of the model and enjoy smooth modifications of the whole model.

Let’s hide all constraints icons (using “Hide All” button from “Geometric” panel of “Parametric” tab), and do the same drags of the same points as we did on Fig. 25 and Fig. 26.

You can drag other points of the “Car” model and enjoy the same smooth modification of the model by Cheetah solver.

This demo demonstrates that AutoCAD in combination with Cheetah solver might become a nice tool for *concept design*, where designer usually do a lot of modification of his model to find the best one. Fast and robust constraints solver is a must to have in such a work.

As you can see in this demo, AutoCAD with its native solver is not able to do this job.