Q:

servo not strong enough to move robotic link fully

I'm currently working on a robotic arm.  The servo I'm using is the MG996R. i'm trying to make the servo lift a link that weights 55 grams and 20 inches long.  The servo itself is powered with a 9v to 7v LM2596 voltage regulator(i'm only using one 9v dura cell battery).  however, the servo will only go from 270 degrees to 180.  if i want to go from 180 degrees to 0 degrees, i will have to manually move the arm in position.  The stall torque for the servo is 12kg * cm. 
so my question is that do i need more power or the servo is not strong enough and that i need to decrease the weight of the arm? 
Links for the servo i bought and a robotic arm calculator that i use to get an idea of the torque that i might need
http://www.ebay.com/itm/4Pcs-MG996R-Digital-Metal-Gear-Servo-High-Torque-Upgraded-MG995-MG945-RC-Model-Y-/281830599332?hash=item419e69aaa4:g:NXcAAOSwI-BWIbDG
http://www.robotshop.com/blog/en/robot-arm-torque-calculator-9712

A:

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.