Newbie here. This is my first time on 3D modeling, rigging, and Blender. I followed an old tutorial on how to make a simple mech and make it move. Because of it being old and lots of things already changed on v2.7, I resolved on following other tutorials.
So this is what's happening - the whole mech/mesh is just only one entity, I joined multiple parts of it using the shortcut CtrlJ before I added armature. Then used CtrlP > Armature Deform with Automatic Weights.
On Pose Mode, few bones works properly, but most are not. Based on the image I attached below, some parts were left out or others are getting stuck/stretched.