I want to use 8 outputs Mashushita PLC (with maximum 10ms of pulse output) as my controller for my robotic arm, so what type of motor should I choose to drive the 4 axis of rotation (base, elbow, shoulder, wrist)? A DC servo motor or DC gear motor or DC stepper motor?? Any suggestion??

 

I've never built any robotic arms (although I played around programming a stepper based arm during a night course many years ago), but it seems to me you'd want to figure out the mechanics of the thing first, at least in general terms, and then select motors that will produce the required torques and speeds, and that will physically fit into the available space.

 

There are robots using servo and stepper on market, so both can do. It very much depends on the dynamic, accuracy and cost.

 

Low performance, low cost, open loop = step
closed loop, higher accuracy, performance, quieter = Brushless DC motor

Most robots of this type use some kind of mechanical reduction.