The use of hardware-in-the-loop (HIL) simulations to reduce
development time and costs has been increasing rapidly in the
robotics industry. At its core, HIL is a form of real-time
simulation. It differs from a pure real-time simulation in that
a real physical component (the component being tested) is added
to the loop. A software model of the plant is created to
simulate the system and provide all necessary electrical signals
to send to a controller; essentially fooling the physical
component into thinking it's operating in a real environment,
with real-world inputs and outputs, and in real-time. The
effectiveness of such a simulation relies on the fidelity of the
plant model. Unfortunately, high-fidelity system models are
rarely deployed for HIL simulations for two reasons: they can be
difficult to develop, and they're too slow for real-time
simulations. Consequently, there's always a compromise between
model fidelity and simulation speed. Causal vs. acausal physical
modeling In the traditional signal-flow