You could increase the size of the pattern, but there's quite a decent amount more work involved in terms of getting motors to fit. The pattern is designed for hobby micro-size servos. By switching to steppers or DC motors, you would have to figure out new mounting plates. Certain servos have the advantage of position control, which you will need to control each of the arm joints. Using DC motors will likely get you better power, but you may have to install potentiometers or some other method or closing the position feedback loop.