  We study a system of coupled pendula with diffusive interactions, which could
depend both on positions and on momenta. The coupling structure is defined by
an undirected network, while the dynamic equations are derived from a
Hamiltonian; as such, the energy is conserved. We provide sufficient conditions
on the energy for bounded motion, identifying the oscillatory regime. We also
describe the bifurcations of synchronised states, exploiting the quantities
related to the network structure. Moreover, we consider patterns of
anti-synchrony arising from the specific properties of the model. Such patterns
can be linked to global properties of the system by looking at motion of the
centre of mass. Nonetheless, the anti-synchrony patterns play also a relevant
role in the bifurcation analysis. For the case of graphs with a large number of
nodes, we characterise the parameter range in which the bifurcations occur. We
complement the analysis with some numerical simulations showing the interplay
between bifurcations of the origin and transitions to chaos of nearby orbits. A
key feature is that the observed chaotic regime emerges at low energies.
