Well I agree with johnwasser . There was some confusion and now it works in the range 1000-2000 with esc.writeMicroseconds
The motor starts spining at around 1030-1050 but after 1500 range is received I doubt the speed is constant till 2000.
I can't visually see or hear any change in speed.
I am really sorry if that is a stupid question it was just my doubt so I asked but I still can't understand why motor stops at esc.write(170-180) though it should be having full speed at that time