There are many papers that use "servo" to motor the robot, but the base nodes of Webots 2019a don't include "servo". what's the difference between "servo" and "HingeJoint"? Should I use the "servo" node if I want to know the joint position? The robot that I have made shows in the picture. my robot
The Servo node was an old node that was replaced by the Slider and HingeJoint.
With the Hingejoint, if you want to get the position of the Joint, you simply have to add a PositionSensor node in the 'device' field of the HingeJoint (as well as a Motor device to control it).
In new version of Webots, we did create a Servo PROTO which uses internally the HingeJoint node (and already includes a PositionSensors and a Motors). So you can either use one or the other as you prefer (result will be the same).
