Payload and Reach
Payload and reach are two of the first numbers you check when sizing up a robot arm, much like the carrying capacity and the wingspan of someone moving boxes. Payload is the maximum weight the robot can safely hold and move at the end of its arm — not just the object itself, but also whatever gripper, suction cup, or tool is attached to do the holding. Reach is how far the arm can stretch out from its base, which sets the size of the space it can actually touch: a long-reach arm can serve a big work area, a short one only what is close by.
These two numbers pull against each other and against the rest of the design, which is why picking a robot is a balancing act. Holding more weight far out at the tip puts more strain on the motors and joints, so a robot rated for a heavy payload usually has a shorter reach, or must move more slowly and carry a sturdier, heavier build. Quote a payload too low and the arm strains, sags, or shuts down on safety; specify a reach too short and it simply cannot get to the far corner of the table. Engineers match both to the job — a delicate arm placing tiny electronic parts needs little payload but fine, precise reach, while an arm stacking crates onto a pallet needs a hefty payload and enough reach to span the whole stack.
A small workbench arm might be rated for a 3-kilogram payload and an 850-millimeter reach — fine for assembling a phone, but unable to lift a full paint bucket or touch a shelf across the room.
Both numbers together tell you what a robot can lift and how far it can lift it — and where it falls short.
A maker's payload figure usually includes the gripper or tool, so the actual weight of the object you can lift is the rated payload minus whatever you bolt onto the end.