BodyDef bd = new BodyDef();
bd.type = BodyType.DYNAMIC;
bd.position.set(0.0f, 7.0f);
Body body = world.createBody(bd);
body.createFixture(shape, 2.0f);
RevoluteJointDef rjd = new RevoluteJointDef();
rjd.initialize(prevBody, body, new Vec2(0.0f, 5.0f));
rjd.motorSpeed = 1.0f * MathUtils.PI;
rjd.maxMotorTorque = 20000;