Payload and travel path decide the type
What the robot has to move, and how far, narrows the field faster than anything else. Small totes and shelves suit a carrying AMR; full pallets up to around a tonne need a pallet AMR or an autonomous forklift; trolleys and trains that already exist are better towed than rebuilt. Distance matters too, because a long haul makes a tugger pulling several carts more sensible than several robots each carrying one.

