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RevoluteJoint

The RevoluteJoint forces two bodies to share a common anchor point around which the bodies rotate. More...

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Properties

• enableLimit : bool
• enableMotor : bool
• localAnchorA : point
• localAnchorB : point
• lowerAngle : real
• maxMotorTorque : real
• motorSpeed : real
• upperAngle : real

Detailed Description

The RevoluteJoint rotates two bodies around a common anchor point with a single degree of freedom: the relative rotation of the two bodies. The relative angle between the bodies is 0 after connection and is positive when bodyB rotates counter-clockwise about the localAnchorA.

To control the angle between two bodies there are 2 options:

Limit the Angle

You can set the lowerAngle and upperAngle property to limit the angle between two bodies. To enable these limits, set enableLimit to true.

Motor Torque and Speed

For applying a torque about the localAnchorA, you can set the motorSpeed and maxMotorTorque properties. For enabling them, set enableMotor to true.

For a comprehensive documentation of all joints see the Box2D documentation at http://www.box2d.org/manual.html#_Toc258082974.

Example Usage

The following example shows how two physics bodies connected with a RevoluteJoint and the motor torque is toggled by clicking on the Scene. By pressing the left and right keys, the motor speed is modified. The source code of the full example is provided in the revolute folder of the Box2D Examples.

 import QtQuick 2.0
 import Felgo 4.0


 GameWindow {
     id: screen

     Keys.onPressed: onKeysPressed(event)

     function onKeysPressed(event) {
         if (event.key === Qt.Key_Left) {
             revolute.motorSpeed += 5
             console.debug("decreasing motor speed to", revolute.motorSpeed)
         }
         else if (event.key === Qt.Key_Right) {
             revolute.motorSpeed -= 5
             console.debug("increasing motor speed to", revolute.motorSpeed)
         }
     }

     Scene {

         PhysicsWorld {
             id: world
             anchors.fill: parent
             z:1 // for putting the debugDraw on top of the entities in QML renderer
         }

         Wall {
             id: ground
             height: 20
             anchors { left: parent.left; right: parent.right; top: parent.bottom }
         }
         Wall {
             id: ceiling
             height: 20
             anchors { left: parent.left; right: parent.right; bottom: parent.top }
         }
         Wall {
             id: leftWall
             width: 20
             anchors { right: parent.left; bottom: ground.top; top: ceiling.bottom }
         }
         Wall {
             id: rightWall
             width: 20
             anchors { left: parent.right; bottom: ground.top; top: ceiling.bottom }
         }

         Square {
             id: rod

             x: world.width/2+middleBall.radius+15
             y: world.height/2

             width: 80
             height: 20
         }

         Ball {
             id: middleBall

             x: world.width/2
             y: world.height/2
             radius: 20
         }

         RevoluteJoint {
             id: revolute
             maxMotorTorque: 30000
             // initially, the speed is 0 - it gets modified by pressing left and right keys
             motorSpeed: 0
             bodyA: middleBall.body
             bodyB: rod.body
             enableMotor: true // start with enabled motor, to toggle click on the window
         }

         Text {
           z: 1 // put on top of DebugDraw in QML renderer
           color: "white"
           text: "Press left and right keys to change the RevoluteJoint motorSpeed"
         }

     } // end of Scene

     EntityManager {
       id: entityManager
     }

     MouseArea {
         anchors.fill: parent
         onClicked: revolute.enableMotor = !revolute.enableMotor
     }
 }

Property Documentation