I also found that when building a piloted bot, it works well to make the stomach section the cockpit, and use the chest up as a lid over the cabin. I use the spine of the mech as the point of rotation for the upper body. Permalink
I tend to use the exo-force click joints for my mechs. I have also found that you can do some interesting things with the 90 degree direction change pieces that are 1x2 studs on each face. I too find that putting the pilot in the torso seems to work best. Permalink
I am currently away from my Lego, but have been covering a lot of bone anatomy recently (working in orthopaedics in Vietnam, of all places).
I have made a few realisations about how to achieve super strong but super flexible joints.
1. No joint is strong enough on its own, you need frictional support (such as cantilevers to subsidiary joints, or "functional elements" such as 87617/87618).
2. Shoulders need a HUGE range of movement, but also stability. People use a single ball and socket, which is so vastly wrong, even the human body doesn't do it! The shoulder is actually 3 seperate joints: The glenohumeral (ball and socket), the acromioclavicular (top of socket to clavicle, which acts as a lever) and the sternoclavicular (fulcrum of said lever).
In order to have a full hemisphere of movement (plus rotation), use the ball and socket for half of the range and the levering up/forward of the socket for the other half. This is what the body does. For abduction of the arm, 90 degrees use the B/S joint, and the upper 90 degrees use the rotation of the scapula (the socket) around the acromioclavicular joint. For rotation of the arm, the 10 degrees around the resting position use the B/S joint, the outer 20 (in either direction) use the retraction and protraction of the scapula.
3. The other benefit of having several joints in one joint is that muscles (or pistons etc.) can go between the body and the scapula, and then the scapula and the arm. This means they do not, if done correctly, impede movements.
4. I should buy lots of 32474 and 53585. They are ideal for being the origin and insertion of "muscles".
5. The gluteus maximus (also the iliopsoas) is used for hip flexion/extension. To emulate its stabilising power, attach a backwards-protruding free-moving lever from the greater trochanter, and put some sort of piston from it up to the small of the back (ending with a B/S joint) and another down from its tip to a point on the back of the distal femur. If done correctly, you can have a full range of flexion and extension, with lots of strength.
Hip adduction and abduction are a little easier because they need much less range. Rotation is also easy because it needs very little range, and very little strength.
I hope these are useful. TBWTMT managed to build a 3 foot transformer, so some people clearly have sussed this already, and I would love to see how they do the joints! However for the rest of us I figured this might be useful. I will also put this in the equivalent TF thread. Permalink