  The navigation of micro-robots in complex flow environments is controlled by
rheotaxis, the reorientation with respect to flow gradients. Here we
demonstrate how payloads can be exploited to enhance the motion against flows.
Using fully resolved hydrodynamic simulations, the mechanisms are described
that allow micro-robots of different shapes to reorient upstream. We find that
cargo pullers are the fastest at most flow strengths, but pushers feature a
non-trivial optimum as a function of the counter flow strength. Moreover, the
rheotactic performance can be maximised by tuning the micro-robot shape or
cargo size. These results may be used to control micro-swimmer navigation, but
they also apply to rheotaxis in microbial ecology and the prevention of
bacterial contamination dynamics.
