  Simulating soft robots in cluttered environments remains an open problem due
to the challenge of capturing complex dynamics and interactions with the
environment. Furthermore, fast simulation is desired for quickly exploring
robot behaviors in the context of motion planning. In this paper, we examine a
particular class of inflated-beam soft growing robots called "vine robots", and
present a dynamics simulator that captures general behaviors, handles
robot-object interactions, and runs faster than real time. The simulator
framework uses a simplified multi-link, rigid-body model with contact
constraints. To narrow the sim-to-real gap, we develop methods for fitting
model parameters based on video data of a robot in motion and in contact with
an environment. We provide examples of simulations, including several with fit
parameters, to show the qualitative and quantitative agreement between
simulated and real behaviors. Our work demonstrates the capabilities of this
high-speed dynamics simulator and its potential for use in the control of soft
robots.
