The Stephenson Value mechanism on a locomotive is a mechanism that the Linkage program can’t simulate. I was asked by a user for help with a box transport mechanism and I see that it is another mechanism with the same issue

Box Transport Mechanism

In case that YouTube video no longer exists, here is a still image of the mechanism:


Box Transport Mechanism

The link in the lower right cannot be simulated because the position of the link cannot be predicted in a single step. Each of the three connections are made to links that can move. There is no way for the simulator to figure out the location of any one of those connections until all three have been computed.

I wrote a post about this issue a long time ago. The only way that I have thought to simulate this is to iterate through all possible positions of one of the connectors while testing the other connections to see what fits.