Internal Structure of Mortar Headd
Joints Integrated with the Keel:
Head Joint (Collar Bone)
In a similar manner to the human skull, the rear part of the head is fixed to the spine of the main frame. The head and neck are moved up and down, left and right by the collar bone joints.
The two main shafts set between the neck and body seen on most MH have the same capabilities as the equivalent human parts, able to reproduce the complex movements involved in lowering the jaw or tilting the neck.
The MH head itself contains little more equipment than the eyeballs and scanners for exterior data collection. The most important being the "Fatima" brain, the Fatima cockpit is encased in a sturdy capsule called the "Fatima Shell". In order to twist the neck the two shafts are moved in opposite directions to turn the face to the side.
Shoulder Joint (Shoulder Blade)
The arms are set upon the shoulder blades of the main frame, based at the neck. The shoulder blade, collar bone, and upper arm power cylinders are linked together into an interlocking unit. Unlike a toy robot, the arm is not connected to the body by a single rotating shaft. Like a human, the shoulder itself moves up and down to raise and lower the arm.
The arm to body connection is strongly linked to the shoulder blade and collar bone, with two thick support arms above and below. The reciprocal movement of these arms shifts the upper arm forward and back, left and right. As with a human, the main pivot point is the shoulder blade. If this is damaged the arm can no longer be moved, but between the collar bones alongside the cockpit and the most solid armor on the back, breaking the shoulder blade is next to impossible. Due to the solidity of the shoulder blade setup, many MH leave this area exposed, as it won’t easily be destroyed anyway.
Among the shoulder blade and collar bone is installed the Ezlazer energy converting "Function Turbine", whose exhaust heat is expelled below the shoulder blade. See the later "Engine and Output Management" section.
Please move your own arm and feel the movement of your own collar bone and shoulder blade to confirm how this works. A MH also moves like that under the armor. At the least, have you now understood that a MH’s movement is not defined by the exoskeletal form of its armored appearance?
Tissue System ~ Joints and Drive System
The drive system serves generally the same purpose as the muscles and tendons in a human body. This is generally called the "tissue system". The most important parts of the tissue system are the shoulder blade internal power cylinders that are the basis of arm movement, the abdominal portion of the keel that twists the body, and the thigh power cylinders that drive the legs.
For the robots of Joker with over a thousand years of history behind them, these three parts are the most important; from the arms to the hands and fingers, knees and heels, put bluntly, are there "just because". While they are a natural progression to the ends of the limbs, their presence does not significantly improve anything.
Essentially, having extras like fingers and heels does not have any real effect on the frame or power figures. There is enough margin to accommodate these without issue. This is evidenced by the presence of heel-less MH walking on their toes (volume 9’s Scritti), heels flush with the ground (Knight of Gold, etc. up to volume 3), and even dancing around in high-heels (Jagd Mirage). The extremities of the limbs can be chosen according to the knight or meisters preferences without regard to power balance and stability.
The drive system consists of the active parts that move the MH’s tendons and pistons, allowing it to reach out and walk. Surprisingly, the particulars of the drive system have never been published, so many people have been left in the dark as to whether the MH joints are run by motors, or the pistons driven by hydraulics or not. Even after all these years, I still find places where I go "huh?" when noticing a lack of explanations.