An inverted pendulum that is balanced on a cart by a delayed linear
feedback force is a model experiment to study delay effects in control
problems. Mathematically, the experiment can be described by
delay-differential equations (DDEs). The region of stability of the
origin (the upside-down position) is bounded for positive delay and
shrinks to zero if the delay reaches a critical value. At this critical
delay the linearization has a triple-zero eigenvalue. We investigate
the neighborhood of this bifurcation to find stable dynamic regimes
that correspond to successful balancing, for example stable periodic
motions of different types and also chaotic regimes. The main tools for
our study are center manifold reduction techniques for DDEs, numerical
bifurcation analysis, and computations of invariant manifolds.