Payload is quoted by the manufacturer as a single number, for example 10 kg, but it is really a combination of mass and where that mass sits. A light part held far from the flange creates the same load on the gearboxes as a heavy part held close, so datasheets include a load diagram with allowed centre of gravity distances and moments of inertia.
The tool counts. A 10 kg arm with a 3.5 kg vacuum head and a 0.5 kg camera bracket has about 6 kg left for the product. Many robots also allow less payload at full reach or at maximum speed.
Overloading rarely breaks anything instantly; it shows up as vibration, drifting accuracy and premature gearbox wear.
