How to calculate the required torque of a stepper motor without spec. appliances?

Question

Arduino

Greetings!
There is a shaft with a roll of paper, you need to constantly wind it around it, I want to adapt a stepper motor so that I don’t have to do it manually.
The question arose about choosing an engine, and since the installation site is limited, I don’t want to overdo it with dimensions, but that there would be enough torque. The speeds are planned to be low - a maximum of 5 revolutions per minute, the drive is direct (there is no place for a gearbox).
I'm thinking of attaching a lever 1 cm long to the shaft and using the "bearing bench" to find out at how many kilograms the shaft with a fully wound bobbin will budge.
For example, it will turn out 3 kg * cm, will the nema17 form factor engine (4.4 kg * cm - with a margin) be suitable to start rotating and maintain the speed of rotation of the shaft, or have I missed something?

Answer 1

If your system implies a smooth start and stop, then yes, 42x35 or more is enough. If accuracy is important - you need to know the weight of the roll - maybe the 86th is not enough.
You can roughly calculate the moment you need as follows:
"mass of paper on the shaft in kg" * 5 * ("roll radius in m") ^ 2 * "required angular acceleration" <= "moment of SD in kg * cm" / 10