Figure 4. Qualitative experiments of assembly.

(a) Assembly under low rotation rate (4–5 Hz). The large attractive zone as a result of the slow rotation yields unsuccessful assembly when the orbital distance is very large (top) and successful assembly when the orbital distance is smaller (bottom). (b) Assembly under moderate rotation rate (10 Hz). The small attractive zone as a result of the increased rotation rate yields unsuccessful assembly when the orbital distance is very small (top) and successful assembly when the swimmer approaches the single bead at a very small α (bottom). (c) Assembly under fast rotation rate (20–25 Hz). The attractive zone becomes very small due of the fast rotation rate which results in the single particle being repelled radial causing a very large orbital distance and failure of assembly (top). Successful assembly was possible when the swimmer approach the single bead at a very small α, similar to (b) (bottom). (d) Initial α was small resulting in very small orbital distances and trapping in magnetohydrodynamic stagnation region in front of swimmer. When α was increased by steering the swimmer to different direction, assembly became possible.