If you notice in the datasheet, for the weight it says that it is at the wrist.
Having said that, usually there isn't any standard calculation method for robotic arms. It is basically striking a balance between:
maximizing the load (to satisfy marketing)
minimizing the load (to make the legal team stop complaining about possible lawsuits).
There was one ...
Gearboxes are very convenient to integrate with stepper motors, and sounds like the most likely solution by far. Just for completeness, some other options are:
Don't know if this counts, but something fairly common that is a gear, but not a "standard NEMA-xx gearbox", would be a worm gear.
Timing belt with the appropriate reduction. The belts have ...
Actually if you want to keep accuracy and increase the torque you can use a gearbox that reduces the input Rpm.
So you will be Sacrificing the speed for the increased torque and precision.
Its also linear so if you need to go from 200gr to a kg you need a great ratio of. 5.
If you had to go higher than 10 then the forces would be significant and you'd need ...
Some use omni wheels, others use mecanum wheels.
It can also just sit the stack down on it's legs when turning if it needs to.
Ok I think I understand the intention now. Here is a thought of how to do it with timing belts. 6 half axles and 2 common shafts M1 and M2.
All 6 half axles would all need to be horizontally adjustable to tension the 6 belts. Everything could mount to "2D" vertically oriented sheet metal or laser cut parts, and the same shafts, bearings, and ...
There are several possibilities depending on what it is you are trying to achieve with your motors.
As Pete pointed out, just syncing all your wheels would KEEP things the same phase (180 deg) apart.
Next up: the thing your diagram seems to represent - two sets where two outer 'wheels' and the middle 'wheel' of the opposite side are in sync. This allows you ...