Do you have an approximate piece count? I was wanting to try some design concepts on this, but it is extremely advanced. Would it be possible to combine a 2D printer into the same unit?
The injection molded K'nex pieces would need to be heated to 360 degrees to melt it into a base plate. It would be much easier to place the base plate's mold under the extruder, but then the base plate would have the same melting point as the filament. Polypropylene also has a high melting point (can also be boiled), but would be more than 100 degrees less.
Yellow 5-way connectors sliding along each other would not be very smooth, as the tops of connectors are usually not flat. It would be smoother to slide along a long rod through a connector. For the design in image 5, if the yellow rod the wheels spin around can be anchored with a 1-way connector that allows free rotation and clips to a rod at the center of the yellow connector, that would reduce the resistance. The motor can be 12 or 24 volts, just depends on the power supply.