Proper way of attaching bones to the model 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.
The automatic weights calculation takes normals into consideration. Since you joined multiple meshes together, typically the normals become inconsistent.

What you need to do is go into edit mode, hit Mesh - Normals - Recalculate Outside. Then unparent the mesh (Alt+p), remove the armature modifier, and do it again (select mesh, select armature, Ctrl+P with automatic weights).

Also another method is leave all meshes separate, and parent each piece to a bone (select mesh, select bone in pose mode, ctrl+p and select bone), which is good for mechanical type armature deform. The downside to this is I find this method VERY slow in game engine if you are using that.