Motor for robot arm

Projects General Guidance
1

I have this robot arm and I'm wondering which stepper motor has enough torque to pull the arm up and to let it back down (2directions). We also have to move it forward and backwards (2directions).

I'm using an Arduino Mega but I'm not sure if we need an extra power source for the 4 motors and what type.

I tried this with stepper motor 28BYJ-48 5VDC but they aren't strong enough.

Any recomondations or programmering tips would be more than welcome!

2

Do you have a link to the arm? Or a name?

If someone put that much effort into designing it, they probably did so with a specific motor in mind. Hobby servos are popular for DIY robot arms.