servo not strong enough to move robotic link fully
There should be no need to ask us. Use a DMM to measure the nominal 7 volts, and verify that this is correct with no load. Now drive your servo into stall. Is the 7 volts still good? If not, measure the battery voltage. Is it still about 9 volts? 

If the battery voltage has fallen, you know that the battery will not provide the power you need.

If the battery is good, but the regulator output has fallen, you know that the regulator cannot provide the current required. 

If both the battery and the regulator are working correctly, the servo is not providing enough torque.