Was the servo powered by the Arduino?
Is the ESC getting power from a separate battery?
I ask because if the external device (be it servo or ESC) is being powered by a separate battery, then the grounds from the Arduino and the battery need to be tied together. Communications between the two will not work without a common ground.
Only the grounds though. Do not tie the Positive lines together.
Yup seperate battery, you were right! i tied up the grounds and it now works perfectly !
What modifications do i need to do to make it work ?
You need to find out the proper 'arming sequence' servo commands your ESC requires before it will actually control the motor, and place that command sequence into your start-up code in your sketch. This is a safety feature of most all ESCs so that it doesn't start up powering the motor when first turned on. On several of mine the sequence is command to 100% (2 millisec PPM signal) for 1 second, command to 0% for one second (1 millsec PPM signal), then ESC beeps and will except any motor command from 0% to 100%. Your ESC sequence may be different, so look for the proper information for your unit.
I have something that i found out, i need to write '90' (center) each time before i tell him to start spining to diffrent side that he is currently spining, i have a continuous rotation servo
How can i found out my 'arming-sequence'?