Earlier quoted context omitted.
seems i lack vision. should i use a stepper or a servo for the robot arm i'm designing ? Stepper motors are best for precise, open-loop control applications where position and speed can be accurately controlled. They are also a good choice for low-speed, high-torque applications. However, they tend to be less efficient than servo motors and can generate more heat. Servo motors are best for closed-loop control applica…
This advice is not good. Robot arms should use harmonic drive gearboxes and servos, IMO. In practice, if the loads are not massively high, the important thing is closed loop steppers or servos, with accurate homing routines and good error handling.
3-phase servomotors (which used to be called "brushless DC servomotors") are much more available than they used to be. Drone motors are tiny 3-phase motors, and can be controlled as servomotors. The drone industry has done a lot to make such motors cheaper. The controllers are much smaller and cheaper now, too. They used to be the size of a book or worse. But they're still more expensive than they should be. I was once at a trade show talking to a rep from a motor company I'd used, and noticed they now sold controllers, too. He said, yes, they had to get into the business because others were selling controllers for 10x the cost of the motor, and they cost about the same to make.
For a long time, you had to bolt the encoder on the back of the motor, and encoders cost way too much. Motors with built-in encoders have become more common.
"RC servos" from model aircraft are cheap, but crappy actuators. They're advancing from 1970s pulse width modulation control to 1980s serial, and for under $20 you can now get some force feedback.