Payload, reach, moment – how a handling device is really sized

The one formula that carries everything

The tilting moment is load times reach: M = F × l. A hundred kilograms at one metre produce the same moment as fifty kilograms at two – to the column both cases are identical. That is why an honest data sheet never states a payload alone but always a pair of load and reach. Comparing peak loads alone means comparing the wrong number.

• M = F × l – moment from load and reach
• F covers part, gripper and lifting accessories, not the part alone
• l runs to the centre of gravity of the load, not to the suspension point
• With a tilted load, l grows further
• Moment and vertical force arrive at the base together

A worked example anyone can follow

A gearbox weighs 90 kilograms, the form gripper 25, the lifting accessory 3. That is 118 kilograms, not 90. Maximum reach is 2.8 metres, and the centre of gravity of the load sits a further 0.15 metres beyond: 2.95 metres. The moment at the base therefore comes to around 3,400 newton metres, calculated at 9.81 metres per second squared. A unit advertised at “125 kg” but rated for only 2,500 newton metres is too small for this station, even though the payload looks right on paper.

What hand-guided units additionally need

A hand-guided load is accelerated and braked, often abruptly. Static calculation alone is therefore not enough. We allow a surcharge for dynamic loading and check the worst case: full reach, full load, movement across the arm direction. That case is rare in service – but when it occurs, the unit has to take it without the operator noticing.

The floor is part of the design

Two quantities arrive at the base of a floor column: the tilting moment and the vertical force from load and dead weight. Both produce tension and compression in the anchors – with usual flange dimensions, a multiple of the payload. Whether dowelling into an industrial floor suffices depends on slab thickness, reinforcement and edge distance. We calculate that before quoting, because a foundation discovered later blows both cost and schedule. In the large majority of cases dowelling is enough.

Rules of thumb for a first estimate

Three approximations are enough for a phone conversation. First: allow 15 per cent of the part mass for the gripper, 25 for vacuum beams. Second: the reach needed is the greatest distance between two working points plus half a metre of allowance. Third: anyone positioning a load rather than only moving it needs a rigid arm – and therefore a unit whose moment rating matches its reach. That does not replace the proper calculation, but it prevents the wrong order of magnitude.