This tutorial is similar to the demo_crank example, but here a small user-interface is created, so that the user can play with a slider to modify the speed of the motor.
The user interface is created with simple GUI features of Irrlicht, but other kind of interfaces/visualization systems could be used.
Here you can also learn:
how to make a four-bar linkage
an example of how to plot/fetch data during the simulation.
use a direct solver instead of iterative solver, for highest precision.