Just downloaded the Box2D wrapper and tried to compile it and got this error.
"SXPhysics/SXPhysics/Classes/Joints/SXGearJoint.h:15:14: Existing instance variable 'joint1' for property 'joint1' with assign attribute must be __unsafe_unretained"
Also I couldn't see where Sparrow was included in the physics XCode project? I presume it's in there somewhere, but I'm used to seeing an actual Sparrow project inside my own project, but it doesn't seem to be in that physics example?