I have an LD-20MG digital servo from Lobot. I connected a 7.4V 2AH LiPo battery to the negative and positive inputs of the motor. Then I plugged the control pin into the PWM digital pin 9 and ran the Sweep example code from the Servo.h library. Nothing happened. No motor noises. Nothing. The motor page said that the motor has an operating voltage of 6.6V to 7.4V and needs to draw at least 1 Amp of power. Is there something I'm doing wrong or understanding about servo motors. Does the board use the 5v and ground pin to create PWM signals? I've gotten it to work before on other smaller servo motors.
Have you got the grounds(0v) connected together ?
The servo may need the control signal to be at the same voltage as that powering it - unsure
Control signal should be o.k. so I bet it is a missing ground connection.
The battery negative needs to be connected to Arduino GND as well as to the servo.
Steve