When using GoPositionXXX functions, the servo reach the desired position (if possible) according to the following rules: 

If the joint axis have defined limits:

• The servo tries to reach the requested position ranged in [limitmin, limitmax]
• The Maintain absolute angle property does not have any effect because servo always have an angle inside [-PI, +PI]

If the joint does not have any rotation limit AND Maintain absolute angle property is checked:

• The servo accumulates every rotation and is able to produce an angle inside ]-inf, +inf[
• The servo reach the requested absolute angular position by making all required 2PI rotations. For example, if the current servo angle is 0 rad and the requested position is 6PI+0.0001 rad : the servo will make 3 complete 2PI rotations + 0.0001 rad.
• If the current position is -180.0° and the requested position is +180.0°, the servo will first go in 0° direction then in +180.0° direction.

If the joint does not have any rotation limit AND Maintain absolute angle property is NOT checked:

• The servo angle is automatically ranged inside [-PI, +PI]
• The desired position is automatically ranged inside [-PI, +PI]
• The servo tries to reach the desired position by using the shortest way
• If the current position is -180.0° and the requested position is +180.0°, the servo will not rotate.
• If the current position is 0.0° (+-delta) and the requested position is +180.0°, the servo can choose to go to +180.0° or -180.0° according to numerical errors (delta)

Step	Description
(Samples/Devices/Servo). Create a joint and select axis, Show the Modify panel then select the Devices sub-panel.
Click on Choose Device icon to open the list of plugins that may be attached to this geometry. Choose Servo Mount As: represents the name of the device in the simulation. Startup: Set it to 'On' to force servo to maintain position 0 (see below).
Double-click on the sensor's reference in order to display/change its settings: Max torque: Servo motor's maximum torque. Max speed: Maximum rotation speed. Min speed: Minimum rotation speed. Accuracy: Acceptable angle error. Min position index: Value of the lowest index for calculating position. Max position index: Value of the highest index for calculating position. Continuous Rotation enabled: Enable/disable continuous rotations (as a simple motor speed command). Maintain absolute angle: Indicates if servo is able to remember all rotations and maintain an absolute global angle. Resistant torques: Static and viscous resistant torques. Set to 0 for disabling this feature. Those parameters override joint's axis: you can disable this behavior by checking the property do not override axis resistive torques (Instance panel). (See also axis settings) Factor: Torque/speed factor: Max Torque=Max Torque * Factor Max speed=Max Speed / Factor
In MODA programming, motors are accessible via the (or DeviceServoMotor class) class. The servo's full path, starting at PHX "/" is hinge0/a1/servo.

Motors and servo-motors