Overview

The first version of the arm will simply be three servos controlled by 3 potentiometers, this allows full manual control over base, shoulder and elbow rotation. This can be controlled with any microcontroller really, but for the schematic i've used the Arduino Nano, as its size is convenient for the PCB. When prototyping this circuit I used both the Arduino Nano and the STM NUCLEO-F401RE. The external power source is necessary as the board itself cannot drive all 3 servos simultaneously. 

Schematic

PCB Design

This was my first time using KiCad, so I kept the design simple as a starting project.

3D-View