Two sizes, and why that is the first decision
The 300 models carry up to 300 kg on an 850 x 480 mm footprint. The 600 models carry up to 600 kg on 950 x 650 mm, and the 600-ST tows 600 kg as a tugger instead of carrying it. Getting this right early saves rework: the payload sets the footprint, and the footprint sets which aisles the robot can actually use once racking, pallets and people are in them.

