Controlling MG946R servo with 3.3v PWM signal
I think you would need a 5V PWM signal to use the full range of speeds/torques of the motor for both types of servos. This components101.com link talks about your motor some and how to control it. An Arduino with 4 independent PWM outputs should work, like the Uno or Atmega2560 version. It looks like you will have to power the servos with a 5V/GND pair that can supply up to 1.2A for the MG946R servo if it stalls. If you try to power it with the wrong pins from, say, an Arduino board you could trip the board or blow a fuse, so make sure whatever pins you use can handle the current max that could be drawn. IIRC the Uno has 6 PWMS and a 5V output pin that can provide enough current for you.