Im currently animating a run cycle for my mech and it seems that the arm joint mesh doesn't want to move with the Chest mesh. I had the mesh joined to the chest mesh. Is there something im missing?
If you switch your armature to Pose mode then your mesh to Weight Paint mode you'll see that the chest bone has zero influence on the arm joints. If you join a mesh to another one Blender can't guess what group the new mesh vertices are supposed to be part of. So use a weight paint brush or assign these vertices to the chest group.