  Active systems contain self-propelled particles and can spontaneously
self-organize into patterns making them attractive candidates for the
self-assembly of smart soft materials. One key limitation of our present
understanding of these materials hinges on the complexity of the microscopic
mechanisms driving its components forward. Here, by combining experiments,
analytical theory and simulations we explore such a mechanism for a class of
active system, modular microswimmers, which self-assemble from colloids and
ion-exchange resins on charged substrates. Our results unveil the self-assembly
processes and the working mechanism of the ion-exchange driven motors
underlying modular microswimmers, which have so far been illusive, even
qualitatively. We apply these motors to show that modular microswimmers can
circumvent corners in complex environments and move uphill. Our work closes a
central knowledge gap in modular microswimmers and provides a facile route to
extract mechanical energy from ion-exchange processes.
