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An Illustrated Guide to Designing Humanoid Robots

Today is the deadline for PAL Robotics’ contest to design the look of REEM-C, the company’s forthcoming full-sized humanoid robot.  I’ve spent the last couple of weeks working on and off on a design to iron out what I felt was the right look for my own entry.  I’ve decided to share my thoughts on the process as it may help others trying to do the same thing in the future.

A quick tour of this blog reveals that I have collected and studied material on hundreds of humanoid robots, which was a bit of an obsession even years before I started this website.  Naturally over the course of that time I have come to favor certain designs or design features above others, and the design process begins by reviewing these.  Whether one has a clear goal in mind of what they intend to design or not, it can be very helpful to gather some reference material.  My personal background is in the video game world, and reviewing reference material is extremely important when designing anything from architecture to fantastic creatures.

Designing A Robot Head

Nexi (MIT), REEM H1 (PAL Robotics), MAVERic (SARCOS, USC)

This article will not be discussing the design of realistic androids with soft skin, but the more abstract mechanical type of humanoid.  Since we’re not creating the next Geminoid, and giving the robot a wig is out of the question, it will have a  hard, bald, or skull-like appearance.  So one of the first things to avoid is a perfectly round, smooth head.  If the robot is meant to look like an infant this is acceptable, but otherwise it may give a frightening or creepy appearance. The face should be smooth – avoid the sharp lines and wrinkles of MAVERic at all costs (unless you want to give the impression of deep scarring).

Helmets, Hats, and Headwear

A common solution to the “bald head problem” is to design a helmet that gives it an irregular shape (which has the side benefit of housing various sensors and other equipment including microphones, cameras, IR distance sensors, speakers and so on).  This can work well if the robot has a specific function and “uniform” such as Murata Boy, which wears a helmet because he rides a bicycle.

HOAP-3 (Fujitsu), Map Robot (Robotech), Tichno (Vstone)

Toyota’s Partner Robots are some of the most successful examples of humanoid robot design.  Their heads come in a variety of styles, from the feather-capped trumpet player to the headphone-and-mic DJ robot.  Their more recent robots, TPR-Robina and the Violin-playing robot, have hair-like head designs which give them a feminine and artistic individuality, respectively.  As a final example, Toyota has published conceptual designs for future Partner Robots that have built-in solar panels in their helmets.

Toyota Partner Robots have unique, aesthetically pleasing head shapes

Function Over Form

Finally, the shape of the head may be dictated by the sensors and other mechanical parts.  This utilitarian approach can result in unique head shapes and “faces” which, while not human-like, can still be related to on some level.  They also avoid the usual pitfalls of more character-based faces, which tend to look like cartoon characters or toys.

PR2 (Willow Garage), TWENDY-ONE (Waseda U.), Assistant (Tokyo U.), SeRoPi (KITECH)

Designing The Eyes, Nose, and Lips

The eyes are the windows to one’s soul, and are the focal point of any face.  Needless to say, the eyes are very important for humanizing the robot’s face, and there are a number of different approaches.  It is quite common for robots to have simple cut-outs for eyes, with cameras sitting inside them.  These eye holes sometimes don’t even contain cameras, but exist to add character; they can and should be embellished with colorful (and color-changing) LED irises to attract attention to them.  These let onlookers know the robot is on, and can reflect the robot’s “emotional state” (an aggressive color like red could be used for “anger”, while a calming blue is soothing, etc.).

QRIO (SONY), NAO (Aldebaran Robotics), Mahru III (KIST, Samsung)

Visor & LED Faces

Some robots hide the eyes and face completely behind a reflective visor or translucent plastic to avoid the issue entirely.  In this situation the robot can be given facial features by employing an LED array.  This works particularly well because we expect a robot to be mechanized rather than organic.  The LEDs can be animated to show different expressions, which are often in the style of simple emoticons.  It can be a simple and effective solution to the robot’s entire face.

SDR-3X (SONY), Mechadroid Type C3 (BDL), Tiro (Hanool Robotics), PALRO (Fuji Soft Inc.)

Screen Heads

Some robots have square heads with a television screen where the face ought to be. This is kind of a lazy approach for humanoid robots, but is sometimes necessary for telepresence applications. Showing a simple face on the screen can be expressive and cute (see Roppie, Mospeng-kun) if a bit simplistic. It is better to crop the face to the screen’s borders rather than showing the full head inside the screen (like FURO), as this can create the impression that the head has been removed and transplanted onto a mechanical body (yuck!).  Of course, if FURO had a more feminine body that matched the face, it would go a long way to improving its overall aesthetic.

Roppie (ITRI), Mospeng-kun (INTERBOTS), FURO (Future Robot)

Eyeballs, Eyelids, and Eye Brows

All of these approaches are valid to some extent but having separate, moving eyeballs is more anatomically correct and therefore probably the direction humanoid robots are headed.  More and more robots are incorporating them, which can be actuated for studying gaze direction, add to emotional expressions, and allow the robot to look around without having to pan or tilt its head.

It is important that the eyes are not too large or too small. According to animation conventions, the characters we are supposed to identify with almost always have large eyes and pupils, while evil characters are drawn with squinted eyes and beady pupils.  For example of a mismatch, look again at this picture of Nexi (left) and MAVERic (far right).  Nexi’s eyes, with the smaller iris and pupil, would be better suited to the more realistic MAVERic head which has large eyes and pupils more suited to young or cute characters.

Eyes that don’t match the rest of the design can be unsettling

If you’re going to include eye balls, it is recommended that the robot also have eyelids.  Blinking, winking, and moving in sync with the eyes (closing slightly when looking downward, and fully open when happy or surprised) adds greatly to a robot’s expressive believability.  The problem with eyelids is that they can sometimes get out of sync with one another, which leads to unpleasant and distracting asymmetry that can make a robot look as though it is drowsy or has a lazy eye.   Another issue is that doll-like eyelids look unnatural – it is best if the eyelids can be attached to the face, which would require the face to be silicone rubber so that it can stretch, wrinkle, and deform.

The Nose

The nose is another tricky area, and many robots do well to avoid one altogether.  If you are insistent on including a nose, there are a few things to consider.  The larger and more pronounced the nose, the more masculine it will appear.  In contrast, the smaller and thinner it is, the more feminine it will appear.  Keeping the nose small, smooth, and subtle as in the following examples imparts a childlike or cherubic appearance.  In my opinion, the more subtle you make the nose, the better (unless you are attempting to create a very realistic face consider removing it altogether).  The following robots have a successful combination of eyeballs, eyelids, and noses, but could be further improved with the addition of eyebrows (the iCub has LED eyebrows which are a bit weird).

Kibo v.1.2 (KIST, CIR), Simon (GATECH), iCub (IIT)

The Lips

The eyebrows, eyes, and lips work together to create facial expressions.  Like the eyes, there are many different approaches including those where a small screen shows animated lips, or where LEDs light up to create different shapes.  The LED solution works to some degree for abstract robot faces, but isn’t ideal for more detailed faces like the iCub.

PaPeRo (NEC), ifbot (Business Design Lab), iRobiQ (Yujin Robot)

Another approach has been used which works quite a bit like a marionette or doll’s lips – what might be called the “claptrap” (as seen in Nexi from MIT).  This simple approach isn’t perfect, but it does have the benefit of an actual lower jaw, which physically opens and closes the mouth.  If combined with a stretchy silicone skin it could look relatively good.  The problem is that the overall shape of the lips remains the same.

ROPID (ROBO-GARAGE), Infanoid (NICT), SCHEMA (Waseda U.)

Another method uses deformable rubber lips that are actuated by a series motors to move and stretch them into different positions to create shapes and expressions.  The effect isn’t perfect, but it give the robot the ability to smile, frown, and so on, which is a boon when communicating during human-robot interaction.  Recently, the Bielefeld University unveiled an innovative new approach to this method which uses magnets to move the lips, so that the actuators can be hidden underneath a solid face, which dramatically improves the look.

REDDY (Robomotion), Kibo (KIST), Flobi (Bielefeld U.)

Finally, an entire face made of silicone rubber that can deform is easily the most successful method of all.  However, this method is almost exclusively used to create realistic human faces, which can lead to the effects of the uncanny valley.  The problem is that the human mouth is capable of subtle movements and deforms at speeds that can’t currently be reproduced.  However, one can see that, based on the results of Hanson Robotics’ ZENO, the effect could be used on less realistic humanoids to great effect.  The one problem with ZENO is that his eyelids aren’t attached to the rest of his face, which could make him look much better.

ZENO’s lips look more natural than most

Designing The Body

You probably want your robot to evoke something familiar rather than something totally strange.  If you take a page from comic books, Superman looks ridiculous in his tights, but at the time he splashed on the scene he evoked the circus strong man, which perfectly suits his character.  ASIMO is a good example of a robot that evokes a well-known figure.  This design was very clever as it allowed Honda to conceal ASIMO’s expressionless face under the visor, while at the same time giving ASIMO a large battery backpack.  When you look at ASIMO, it purposefully evokes an astronaut – a friendly figure not of this world.

ASIMO (Honda) reminds us of an Astronaut

An Iconic Silhouette

To take another page from comic books, if possible the figure should define an iconic, memorable silhouette.  Batman is a good example of this; even completely back lit there is no doubt what superhero you are looking at.  This is almost entirely due to Batman’s perky little ears.  In the robotics world, embellishing  a humanoid with non-human features (like the HRP-2 Promet’s helmet “fins”) is acceptable.  While some may not like its overtly sci-fi / anime appearance (it was designed by a comic book artist), there’s no doubt that it has one of the most memorable silhouettes of all the humanoid robots out there.

HRP-2 Promet’s (AIST, Kawada Industries) unmistakable silhouette

Picking A Color Scheme

The final cue from comic book heroes is to pick a few colors and use them wisely.  Marvel Comics’ Spiderman gets away with mostly bold blues and reds, while X-Men’s Wolverine is yellow, with black sections and a dab of bright red.  In robots, the base color tends to be white or metallic, while bold colorful accents are limited to key areas.  Good examples of this can be seen in Wakamaru (Mitsubishi), HRP-4 (AIST, Kawada Industries), Mahru & Ahra (KIST, Samsung), the P2 and ASIMO (Honda), NAO (Aldebaran Robotics), and ENON (Fujitsu),.

Two-toned color schemes seem to work best

Tomotaka Takahashi (ROBO-GARAGE) mixes bold colors in most of his robots, but his use of complimentary colors (not necessarily the traditional pairings) is done with thought and care.  As a result, his robots have a friendly (if a bit toy-like) appearance, which suits them well.


Mechanical Structure

A robot’s mechanical structure can inform the overall design to dramatic effect.  DLR’s Justin, for example, has oddly shaped actuators which gives the robot an entirely unique appearance.  Kawada Industries’ NEXTAGE was created for pick-and-place manufacturing / processing jobs, so it has oddly-proportioned arms.  The outward appearance of M3-Neony (JEAP, Osaka University) is defined mainly by its tactile sensor array.

Rollin’ Justin (DLR), NEXTAGE (Kawada Industris), M3-Neony (JEAP)

When discussing mechanical design safety is an important consideration, as is maximizing any given joint’s range of motion.  Consider the elbow and knee joints – tricky spots – where the upper link meets the lower link.  Deep cuts are often made where the links intersect in order to ensure that the arm or leg can curl properly.  However, these cuts can also trap fingers at the two extremes.

REEM-B (PAL Robotics), Assistant Robot (Tokyo U.), HUBO 2 (KAIST)

Many different approaches to this problem have been explored.  The first version of Honda’s ASIMO (2000) had large gaps which were covered with an overlapping shield when ASIMO ver.2 (2005) was built to prevent fingers becoming trapped in its joints.

Honda ASIMO version 1 (left), version 2 (right)

The SONY QRIO has an elegant inward curving elbow which virtually eliminates the problem.  SONY also used pressure sensors in these areas so that if the joint closed on something, it would automatically stop and reverse direction.  Safety should be the top priority when designing a robot that will be in close proximity to people.

Overlapping links with curved elbows are an elegant solution to the problem

Indicators & Warning Lights

Robots don’t always have indicator lights, but those that do seem to prefer to place them in highly visible areas such as on the chest or upper back.  LEDs and dot-matrix displays tend to be the preferred styles of showing the robot’s status.  The following image shows the indicators of (top row): ASIMO (Honda); HRP-4 (AIST, Kawada Industries); Wakamaru (Mitsubishi), and (bottom row): TWENDY-ONE (Waseda U.); HUBO 2 (KAIST); and NEXTAGE (Kawada Industries).

Various examples of indicators and warning lights


This concludes the first part of An Illustrated Guide to Designing a Humanoid Robot.  While the design of the robot’s hands and fingers, the use of various sensors, and other considerations have not been presented, I hope this has been an interesting and informative look at some of the major points that go into making a successful humanoid robot design.  Of course, when it comes to design there are no hard rules – and rules are made to be broken! Click here to see how these points were addressed when designing the look of Plastic Pals’ version of REEM-C (as part of PAL Robotics’ contest).

  • Discoman

    fun and informative guide. how about one on androids next, robots like actroid and others that look the most human?
    that would be very interesting, as the design needs to work to mimic people and their appearance, not just be evocative of people.

    • Robotbling

      @ Discoman

      I would if I knew more about the process of making them. Unfortunately there isn’t much to talk about in terms of their outward appearance because the goal is simply to make them look like a person, but the actual fabrication is probably very interesting.

  • deviker

    Thanks! this guide has been very usefull to me ;)

  • Pingback: Le design des robots humanoïdes()

  • alex

    I guess I should clarify this more: “It needs a soft (silicone) face to use eyelids properly.”
    It’s that when you have a robot with big ball eyes -Simon, Flobi- their eyes look creepy themselves but when they add those strange eyelids it’s even more creepy.
    They can use eyelids properly – Kibo, Kibo 1.2, ifbot – their eyes are not such creepy balls and they use the upper eyelids what looks more natural + those robots are not too much human like.
    If the robot tries to look too human like but the eyes and eyelids look too fake it’s probably better to use silicone to make the illusion better – but if that would make it less creepy ??
    I guess ZENO is quite well balanced/designed – he looks like a doll but natural. But because of his big eyes if the eyelids would be attached to his face it could ruin the impression and kick him into the uncanny valley. ZENO prospers from the doll like look – that’s how he can avoid the uncanny valley. With smaller eyes he could look better with attached eyelids.
    Looks like the design of eyes and eyelids has to be well balanced – eyes are just the most important thing of the face.
    I.e. a robot like SONY from movie “I robot” would look great with white silicone face – he looks human like but you can clearly distinguish it’s a robot.

    at Tiro (Hanool Robotics) – they shouldn’t use red leds for the face -> unfriendly, scary

  • Joe Dunfee

    I think that the more a robot is capable of imitating human appearance and actions, the more important it may be to make it look non-thinking or emotional. I can see it being a problem from two different directions;

    If someone perceives the robot as having human-like thought and emotions, the design of the robot has deceived them. That person would have false expectations for the robot.

    From the other side, what if someone considers the same robot to be only a machine. They would ignore its saying, “Thank you.” The person may be conditioning themselves to also ignore the phrase, “Thank you.” when spoken by a fellow human being.

    Perhaps people will be able to keep the fictional human from the real one separate in their minds. But, I tend to prefer that a robot not have a face at all.

  • Very nice. Looking forward to part 2.

  • alex

    Great guide.

    “…(like FURO), as this can create the impression that the head has been removed and transplanted onto a mechanical body”
    – I like the approach of FURO, the problem with it is that the body doesn’t fit it, it would need a nice feminine body. But it’s much less uncanny valley than the robots with a 3D head. If the head is a 2D anime style character there’s no problem with it (it’s a win) it would look awkward if the head would be realistic 3D CG. With a better design a robot with an LCD and an anime face would be just great – a pure win :) 2D>3D

    Eyelids – I think those puppet style eyelids look creepy (Simon, iCub) especially if the robot has creepy big eyes and a human like face…and uncanny valley – you can see they are not “real”/fake. It needs a soft (silicone) face to use eyelids properly.

    I like that display from HRP-4 it looks like an Eva status display from NGE :)

    • Robotbling


      You make some good points. I will update the article to include them.