Hi all, I'm trying to get a (probably dumb) thing to work in PBox2d - to get an arm to point towards the mouse. I have a basic box with a revolute joint and a motor. The rotation works find on it's own.

According to a tutorial I found, I then need to add a mouse joint to direct the motor... but it's not working. My code is pretty lengthy, so perhaps there is someone out there with an example sketch?

Here's my joint definitions:

1.     RevoluteJointDef rev = new RevoluteJointDef();
   
2.     Body world = box2d.getGroundBody();
   
3.     rev.initialize(body, world, world.getWorldCenter());
   
4.     rev.motorSpeed = rotationSpeed;
   
5.     rev.enableMotor = true;
   
6.     joint = (RevoluteJoint) box2d.world.createJoint(rev);
   
7.    
   
8.     MouseJointDef md = new MouseJointDef();
   
9.     md.bodyA = box2d.getGroundBody();
   
10.     md.bodyB = body;
    
11.     md.maxForce = 2000;
    
12.     mouseJoint = (MouseJoint) box2d.world.createJoint(md);
    

And here's the method to rotate the arm:

1. Vec2 mouseCoords = box2d.coordPixelsToWorld(mouseX, mouseY);
   
2. mouseJoint.setTarget(mouseCoords);
   

Ultimately I'd like to implement this with Android so an arm always points down using the accelerometer.

Totally stuck and frustrated - time for a break!