If you want to turn off power for some external parts you could try to power them via the digital pins. See this example code:


    void setup(){
       pinMode(YOUR_ARM_POWER_SUPPLY_PIN, OUTPUT);
    
       // switch arm on
       digitalWrite(YOUR_ARM_POWER_SUPPLY_PIN, ON);
    }
    
    void loop(){
      if(armMustNotUseAnyPower()){
          // switch arm off
          digitalWrite(YOUR_ARM_POWER_SUPPLY_PIN, OFF);
      }
    
    }

Keep in mind that the digital Pins cannot output as much power as VCC. But since you drive some servo motors over it I assume they get their power externally anyway. You might need to add some transistor or another way on how to switch the power on and off from the big power source. Hope this helps you in some way.