RaspberryPi + TowardPro MG996R DIGI HI TORQUE +PWM
Hobby servos are controlled by a pulse width, but this is not the same kind of pulse width modulation that is done by pi-blaster. 

Hobby servos use a periodic pulse at a relatively low rate (50 Hz is typical, but the rate is not critical). Each frame contains a nominal 1.5ms pulse to set the server at its nominal 0° position. Varying that pulse width from 0.5ms to 2.5ms moves the servo over its full mechanical range. If the servo is able to move 90° each way by varying the pulse width by up to 1ms, that is the same as 11.1 µs per degree.

So precise control of that servo requires high resolution control of that pulse, and a relatively long dead time to the next pulse.

PWM as done by pi-blaster is designed to control power by adjusting a pulse from 0% to 100% duty cycle of a 100 Hz clock. To use this to control a hobby servo you need to start by turning the base clock frequency down to something in the 50 Hz ballpark. Some servos may accept control as fast as 100 Hz, but that isn't the usual practice.

Next, you need to limit yourself to the PWM range of 0.025 to 0.125, assuming a 50 Hz PWM clock.

The later limit means that of the default precision of 1000 steps from 0% to 100% duty, you can only use 100. For a 180° motion, that would give you a precision of 1.8° per step.

The better answer is to use software designed to control hobby servos. pi-blaster notes that it was derived from ServoBlaster. Use that. It will be a little trickier to interface with because it is just a kernel driver and doesn't provide the slick ASCII FIFO. 

One other caution: don't wire a hobby servo directly to your RPi. The RPi has 3.3V I/O, but the hobby servo will want to be driven at 5V or more. You should use a suitable level shifter to get the right drive voltage, and to introduce something less expensive than your entire RPi to burn out when something goes wrong.