A Comprehensive Guide to Designing a Humanoid Robot: Considerations and Best Practices
As an industrial designer focused on the design and interaction of robots, I have been designing various types of robots for 9 years. By far, the most enjoyable and challenging designs have been humanoid robot designs. Here, I want to share some tips for both designers and roboticists who are traversing the same path.
Before beginning to design a humanoid robot, the following questions need to be answered:
1- Who is this robot? What personality do you want to give him/her? What feeling/emotion do we want it to evoke in the audience?
2- Who is this robot for? Who should fall in love with this robot at first sight?
3- How visible do we want this robot to be? Is it an introverted or extroverted robot?
4- Where did this robot come from? Did it come from a robotic lab made by people who were trying to push the boundaries of science, or did it come from an industrial enterprise to showcase their capabilities or something else?
5- Which capabilities of this robot do we want to expose to the audience, and which ones need to be hidden?
6- What makes this robot different from others? Or in fact, where is the focus? Is it in the legs like Atlas, or in the hands, like Phoenix, or in communication like Ameca?
7- What is that “one thing” that we want people to remember when they see this robot? It should be one, not two!
8- Last but not least, which areas of this robot are human-like, and which areas are not? In other words, what parts of this robot are directly inspired by humans, and what parts are inspired by other artifacts?
Consider that the same questions above can be asked of an individual. Start by asking these questions of yourself first. A tip for question 8: Are you wearing glasses now?
The above questions guide us through the design process and form the foundation for considering the next steps. Designing a humanoid robot involves these six main areas. A successful humanoid design achieves the best balance given these aspects. Remember to use the answers to the above questions to address these six areas.
1- Proportions: Perhaps the most crucial aspect in humanoid design is proportion. Considering design proportions fulfills both aesthetic and functional goals. Designing proportion does not necessarily mean replicating the exact appearance of a human and measuring it, as there is no perfect human body. Instead, it involves determining which proportions achieve the goals of the robot and are aesthetically pleasing to the human eye. There’s a lengthy discussion on how to approach proportions, but the easiest way is to select a body type based on factors such as age, gender, and capabilities, then establish the relationships between different elements of the body. For example, an adult body that is 180 cm tall typically consists of eight heads stacked on top of each other, with shoulder width equivalent to placing three heads side by side. While practitioners often use a standard mannequin’s mesh, having a strategy for proportions helps address the limitations imposed by the size of actuators and links. The human body employs golden ratios in various locations. Designing the related links based on golden ratios is a recommended practice. For instance, from the shoulder to the last knuckle of the hand, all joints follow the golden ratio rule.
2- Coverability: This aspect defines how much of the system is covered by non-functional panels/covers and how much is exposed. The answers to the above questions can help solve this part. In humanoid design, there are often limitations on what/where to cover and what not to cover. These limitations stem from factors such as degrees of freedom (DoFs), weight limitations, component sensitivity or confidentiality, generated heat, environmental constraints, etc. An easy practice is to first identify which areas need to be covered and which need to be exposed. Start with the certain coverable areas and decide later on the exposed areas based on necessity. Recent trends intentionally avoid full coverage, although this approach requires careful attention to detailed design of the structure and internal components. There are mainly three trends followed in this area: 1- Full coverage: These robots are often highly commercial and intended for direct interaction with humans, as seen in robots such as Asimo, Pepper, or Eve 1X. 2- Partial cover: This type of coverage offers design flexibility and does not overly constrain the technical team, as observed in robots such as Tesla Optimus Gen 1, Surena 4, and Atlas. 3- Exposed structure: In this approach, the inner structure is not separated from the outer non-functional cover. It manifests in two forms: either the inner structure is designed to appear aesthetically pleasing without any non-functional covers, or non-functional covers are designed to look functional and structural. There’s no right or wrong approach here; it all depends on the intended usage of the robot.
3- Forms and geometries: The first question to address here is whether we are designing the forms of the robot based on human bones, muscles, skin, or clothing. For example, when designing the shape of the feet, are we following human feet forms or shoe forms? It’s crucial to establish this at the beginning of the process and maintain consistency. Of course, a mix of all is an option as long as a skeleton with exposed bones isn’t wearing gloves! What we define as basic geometric shapes, which form the basis of most mechanical components such as actuators and standard bars, cannot be found exactly in nature, or in this context, the human body. Therefore, based on the requirements, some compromises must be made. A robot with fully organic and fluid shapes isn’t the most efficient, and a purely geometrical robot isn’t highly desirable. Finding the right balance and mix of forms has a significant impact on the robot’s aesthetics. Some components can contribute to creating more organic forms. For instance, cable sets and wire socks can create organic and fluid forms if exposed. One approach that significantly impacts the balance of forms is the repetition of a certain form. A good practice here is to design a form for each type of actuator or joint and repeat that form wherever the same movement occurs. For instance, a “squircle” transforming into a circle can be used wherever there’s a one-degree-of-freedom joint. However, controlling and balancing forms is much more challenging when the structure is exposed, and various types of elements with different geometries are visible.
4- CMF: Stands for Color, Material, and Finish, and is a common term in design that’s particularly important in robotics design. Balancing CMF in the right way greatly assists in achieving proportions and aesthetics, just as character and personality do. It’s usually recommended to consider one color as the primary color and mix it with monochrome colors. Black and white are inevitable in robot design since most components use these tones. Material can significantly influence how the audience perceives the robot’s functionality. For example, a robot covered in fabric might seem suitable for use in elderly care homes, while a robot with a metal finish might appear more industrial. However, not adhering to stereotypes provides ample room for creativity. The use of raw material components can also enhance the robot’s attractiveness. For instance, the material of the camera lens can be left as is, without additional material on top of it. A common material used in humanoid design is rubber and elastomers, as they provide both coverage and an appealing look. However, manufacturing constraints and the limitations they impose on actuators should be considered. The finish is an area that requires delicate attention from the designer. Finding the right balance between different finish types is a challenging task. A recommended practice here is, similarly to forms, to consider a certain finish and repeat it as a pattern all over the robot. For a more comprehensive color guide check out this blog.
5- Movement: The aforementioned aspects are all relevant and noticeable when the robot is in a stationary mode. However, as soon as the robot starts moving, the audience’s attention shifts to the movements, and other aspects become secondary. Whatever proportions, covers, forms, and CMF are being designed, they should be assessed in relation to the desired movements. In the mechanical and dynamics design of a robot, everything revolves around Degrees of Freedom (DoFs) and Center of Gravity/Mass (CG/CM), so the forms and other elements should be designed with these considerations in mind. A good practice here is to sketch the robot’s concept not only in a stationary mode but also in various movements. Subsequently, observe the robot in simulated movements and assess if its character and appearance change significantly in certain movements.
6- Character: This can be the most challenging aspect of the design; however, if we know what the character should be, it becomes easier. If you have answered the question about the character and personality of your robot, then you need to look for any characteristics that embody that personality. Examining animations and movements that illustrate a particular character can be helpful here. It’s important to note that a robot’s character is not limited to its head, face look, and expressions; it’s evident in every single element of the body. Consistency in the use of certain forms and CMF can aid in conveying character. Additionally, certain characters have corresponding proportions. For example, an agile and quick robot may have thinner legs and avoid using extra panels on the legs.
The design of a humanoid robot involves various aspects to consider and should be done in collaboration with other teams. The aforementioned items are the most basic areas to consider; in addition to them, there are also areas such as lighting, labeling, voice and sound, etc.