When planning any rigging, it is important to have enough reference to understand how something should move, and what kind of limitations it has. With mechs, there is not as much deformation as there would be in organic characters, but there are a lot more limitations on the range of motion. As a result, the design may have to be compromised for functionality. For example, a human arm has plenty of freedom in its mobility, however this also adds complexity because shoulders have so much more range. That makes it difficult to have it deform correctly and may even require working muscles.
Rigging Mechanical Characters
The mech character was one of the first fully rigged characters I did, so there was a lot of learning and exploration I had to do. A major part of my learning was experimenting and making many mistakes in order to reach an understanding of how to get a rig to function properly with all the joint chains, controls, IK handles and set driven keys. I worked with a classmate, Roger Siuraneta Queralt, who designed and modeled the V-T Oversuit, we had to do a lot of bouncing back and forth with changing the rig and model to make it work. Also, since I wasn’t familiar with how a typical animator prefers the controls to work, I was constantly referencing rigs I had seen online. I also considered how I would want it to work if I was doing the animating. In the end, I used a lot of set driven keys to keep as many controls as intuitive as possible.
It wasn't always obvious to tell if a piston or hydraulic would work until the rigging was put into test the geo-crashing and limitations. A lot of iterations were made to make a somewhat believable functioning character. In a lot of concept art, it is not always taken into consideration the practicality of the designs, so when you start modeling the designs will take a hit because it won't actually work and will have to be modified during the rigging stage.
Organization is key for big projects like this especially for final exports to ensure the process is easy for baking the animation down to just joints and skinned mesh. This character was used in a game engine so considerations were made, such as no geo is parented or constrained just smooth skinning with vertex weights at 100% only to one bone. Smooth skin on solid pieces may seem slow compared to just separate objects moving around, but actually runs faster in a game. When exported or imported to the game engine, the geo actually becomes one single mesh (all the objects essentially become combined) meaning smooth skin is needed in the game to move those parts separately. By having it be a single mesh in the game engine, far fewer draw calls are needed, dramatically speeding up realtime rendering.
A good place to start if you are doing a human character for the first time is knowing where to place the joints and how the rotations should be. It is good practice to have all the rotations be be consistent for the main motion with every joint. The X axis should always point to each child joint for twisting movement. The main rotation will come from the Z axis and the Y axis is for the least likely part of movement. So, if the fingers can only curl one way the main rotation will be Z axis, the twist will be X axis and Y will be used for fingers spread all in the positive rotational values. Keeping that set up throughout the whole character will make for a better organized and cleaner rig for animation or any other process down the pipeline.
The skinning process for realistic deformations is the biggest thing to focus on and will be quite a challenge especially for new riggers. There was a lot of testing I did with the Maya muscle system, in order to get the proper placement for the muscles, tweaking the settings so they deform how an actual muscle would. I started out small on a three joint chain and with just one muscle to focus on so I could get the pipeline workflow memorized. The shoulders tend to be a nightmare, especially if you want correct movement and the muscle to deform correctly. The reason why the shoulder is so challenging is because of the balance between the head, neck, clavicle, shoulder and upper chest joints. You have to constantly move the shoulders and the surrounding areas to see if all the parts are deforming correctly. All that being said, knowing anatomy and muscle deformation for not only humans but animals as well is an absolute must. The same goes for having patience in the process, so good luck.
We thank Hayden for providing us with this helpful information!