  Control on microscopic scales depends critically on our ability to manipulate
interactions with different physical fields. The creation of micro-machines
therefore requires us to understand how multiple fields, such as surface
capillary or electro-magnetic, can be used to produce predictable behaviour.
Recently, a spinning micro-raft system was developed that exhibited both static
and dynamic self-assembly [Wang et al. (2017) Sci. Adv. 3, e1602522]. These
rafts employed both capillary and magnetic interactions and, at a critical
driving frequency, would suddenly change from stable orbital patterns to static
assembled structures. In this paper, we explain the dynamics of two interacting
micro-rafts through a combination of theoretical models and experiments. This
is first achieved by identifying the governing physics of the orbital patterns,
the assembled structures, and the collapse separately. We find that the orbital
patterns are determined by the short range capillary interactions between the
disks, while the explanations of the other two behaviours only require the
capillary far field. Finally we combine the three models to explain the
dynamics of a new micro-raft experiment.
