You can manually control two servos with a simple device, the Dual Servo Driver. You can power this unit with a 4.8-6V battery or regulated power supply. Each knob will proportionally control the corresponding servo. The potentiometers can even be taken off and wired away from the board for specialized applications which require the potentiometers to be remotely mounted. The servo will mimic the motion of the corresponding knob. This driver can handle two servos, from nano size to giant scale. To purchase the board and components without the case, click here.