Category robotics

This relatively general post focuses on robotics-related PhD programs in the American educational system. Much of this will not apply to universities in other countries, or to other departments in American universities. This post will take you through the overall life cycle of a PhD and is intended as a basic overview for anyone unfamiliar with the process, whether they are considering a PhD or have a loved one who is currently in a PhD program and just want to learn more about what they are doing. 

The basics

A PhD (doctoral degree) in engineering or a DEng (Doctorate of Engineering) is the highest degree that you can earn in engineering. This is generally a degree that people only earn one of, if they earn one at all. Unlike a bachelor’s degree or a master’s degree, a PhD studying a topic relevant to robotics should be free and students should receive a modest stipend for their living expenses. There are very few stand-alone robotics PhDs programs, so people generally join robotics labs through PhD programs in electrical engineering, computer science, or mechanical engineering. 

Joining a lab

In some programs, students are matched with a lab when they are accepted to the university. This matching is not random: If a university works this way, a professor has to have a space in their lab, see the application, and decide that the student would be a good fit for their lab. Essentially, the professor “hires” the student to join their lab. 

Other programs accept cohorts of students who take courses in the first few years and pick professors to work with by some deadline in the program. The mechanism through which students and professors pair up is usually rotations: Students perform a small research project in each of several labs and then join one of the labs they rotated in. 

The advisor

Regardless of how a student gets matched up with their advisor, the advisor has a lot of power to make their graduate school experience a positive one or a negative one. Someone who is a great advisor for one student may not be a great advisor for another. If you are choosing an advisor, it pays to pay attention to the culture in a lab, and whether you personally feel supported by that environment and the type of mentorship that your advisor offers. In almost every case, this is more important for your success in the PhD program than the specifics of the project you will work on or the prestige of the project, collaborators, or lab. 

Qualifiers

PhD programs typically have qualifiers at some point in the first three years. Some programs use a test-based qualifier system, either creating a specific qualifier test or using tests from final exams of required courses. In some programs, you are tested by a panel of faculty who ask the student questions about course material that they are expected to have learned by this point. In other programs, the student performs a research project and then presents it to a panel of faculty. 

Some universities view the qualifiers as a hurdle that almost all of the admitted PhD students should be able to pass, and some universities view them as a method to weed out students from the PhD program. If you are considering applying to PhD programs, it is worth paying attention to this cultural difference between programs, and not taking it too personally if you do not pass the qualifiers at a school that weeds out half of their students. After all, you were qualified enough to be accepted. It is also important to remember, if you join either kind of program, that if you do not pass your qualifiers, usually what happens is that you leave the program with a free master’s degree. Your time in the program will not be wasted!

Research

Some advisors will start students on a research project as soon as they join the lab, typically by attaching them to an existing project so that they can get a little mentorship before starting their own project. Some advisors will wait until the student is finished with qualifiers. Either way, it is worth knowing that a PhD student’s relationship to their PhD project is likely different from any project they have ever been involved with before. 

For any other research project, there is another person – the advisor, an older graduate student, a post doc – who has designed the project or at least worked with the student to come up with parameters for success. The scope of previous research projects would typically be one semester or one summer, resulting in one or two papers at most. In contrast, a PhD student’s research project is expected to span multiple years (at least three), should result in multiple publications, and is designed primarily by the student. It is not just that the student has ownership over their project, but that they are responsible for it in a way that they have never been responsible for such a large open-ended project before. It is also their primary responsibility – not one project alongside many others. This can be overwhelming for a lot of students, which is why it is impolite to ask a PhD student how much longer they expect their PhD to take. 

The committee

The “committee” is a group of professors that work in a related area to the student’s. Their advisor is on the committee, but it must include other professors as well. Typically, students need to have a mix of professors from their school and at least one other institution. These professors provide ongoing mentorship on the thesis project. They are the primary audience for the thesis proposal and defense, and will ultimately decide what is sufficient for the student to do in order to graduate. If you are a student choosing your committee, keep in mind that you will benefit greatly from having supportive professors on your committee, just like you will benefit from having a supportive advisor. 

Proposing and defending the thesis

When students are expected to propose a thesis project varies widely by program. In some programs, students propose a topic as part of their qualifier process. In others, students have years after finishing their qualifiers to propose a topic – and can propose as little as a semester before they defend! 

The proposal and defense both typically take the form of a presentation followed by questions from the committee and the audience. In the proposal, the student outlines the project they plan to do, and presents criteria that they and their committee should agree on as the required minimum for them to do in order to graduate. The defense makes the case that the student has hit those requirements. 

After the student presents, the committee will ask them some questions, will confer, and then will either tell the student that they passed or failed. It is very uncommon for a PhD student to fail their defense, and it is generally considered a failure on the part of the advisor rather than the student if this happens, because the advisor shouldn’t have let the student present an unfinished thesis. After the defense, there may be some corrections to the written thesis document or even a few extra experiments, but typically the student does not need to present their thesis again in order to graduate.

The bottom line

A PhD is a long training process to teach students how to become independent researchers. Students will take classes and perform research, and will also likely teach or develop coursework. If this is something you’re thinking about, it’s important to learn about what you might be getting yourself into – and if it’s a journey one of your loved ones is starting on, you should know that it’s not just more school!

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Rob Telson

Rob is an AI thought-leader and Vice President of Worldwide Sales at BrainChip, a global tech company that has developed artificial intelligence that learns like a brain, whilst prioritizing efficiency, ultra-low power consumption, and continuous learning. Rob has over 20 years of sales expertise in licensing intellectual property and selling EDA technology and attended Harvard Business School.

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By Alexander Badri-Sprowitz, Alborz Aghamaleki Sarvestani, Metin Sitti and Linda Behringer

If a Tyrannosaurus Rex living 66 million years ago featured a similar leg structure as an ostrich running in the savanna today, then we can assume bird legs stood the test of time – a good example of evolutionary selection.

Graceful, elegant, powerful – flightless birds like the ostrich are a mechanical wonder. Ostriches, some of which weigh over 100kg, run through the savanna at up to 55km/h. The ostrich’s outstanding locomotor performance is thought to be enabled by the animal’s leg structure. Unlike humans, birds fold their feet back when pulling their legs up towards their bodies. Why do the animals do this? Why is this foot movement pattern energy-efficient for walking and running? And can the bird’s leg structure with all its bones, muscles, and tendons be transferred to walking robots?

Alexander Badri-Spröwitz has spent more than five years on these questions. At the Max Planck Institute for Intelligent Systems (MPI-IS), he leads the Dynamic Locomotion Group. His team works at the interface between biology and robotics in the field of biomechanics and neurocontrol. The dynamic locomotion of animals and robots is the group’s main focus.

Together with his doctoral student Alborz Aghamaleki Sarvestani, Badri-Spröwitz has constructed a robot leg that, like its natural model, is energy-efficient: BirdBot needs fewer motors than other machines and could, theoretically, scale to large size. On March 16th, Badri-Spröwitz, Aghamaleki Sarvestani, the roboticist Metin Sitti, a director at MPI-IS, and biology professor Monica A. Daley of the University of California, Irvine, published their research in the renowned journal Science Robotics.

Compliant spring-tendon network made of muscles and tendons

When walking, humans pull their feet up and bend their knees, but feet and toes point forward almost unchanged. It is known that Birds are different — in the swing phase, they fold their feet backward. But what is the function of this motion? Badri-Spröwitz and his team attribute this movement to a mechanical coupling. “It’s not the nervous system, it’s not electrical impulses, it’s not muscle activity,” Badri-Spröwitz explains. “We hypothesized a new function of the foot-leg coupling through a network of muscles and tendons that extends across multiple joints”. These multi-joint muscle-tendon coordinate foot folding in the swing phase. In our robot, we have implemented the coupled mechanics in the leg and foot, which enables energy-efficient and robust robot walking. Our results demonstrating this mechanism in a robot lead us to believe that similar efficiency benefits also hold true for birds,” he explains.

The coupling of the leg and foot joints and the forces and movements involved could be the reason why a large animal like an ostrich can not only run fast but also stand without tiring, the researchers speculate. A person weighing over 100kg can also stand well and for a long time, but only with the knees ‘locked’ in an extended position. If the person were to squat slightly, it becomes strenuous after a few minutes. The bird, however, does not seem to mind its bent leg structure; many birds even stand upright while sleeping. A robotic bird’s leg should be able to do the same: no motor power should be needed to keep the structure standing upright.

Robot walks on treadmill

To test their hypothesis, the researchers built a robotic leg modeled after the leg of a flightless bird. They constructed their artificial bird leg so that its foot features no motor, but instead a joint equipped with a spring and cable mechanism. The foot is mechanically coupled to the rest of the leg’s joints through cables and pulleys. Each leg contains only two motors— the hip joints motor, which swings the leg back and forth, and a small motor that flexes the knee joint to pull the leg up. After assembly, the researchers walked BirdBot on a treadmill to observe the robot’s foot folding and unfolding. “The foot and leg joints don’t need actuation in the stance phase,” says Aghamaleki Sarvestani. “Springs power these joints, and the multi-joint spring-tendon mechanism coordinates joint movements. When the leg is pulled into swing phase, the foot disengages the leg’s spring – or the muscle-tendon spring, as we believe it happens in animals,” Badri-Spröwitz adds. A video shows BirdBot walking in the research group’s laboratory.

Zero effort when standing, and when flexing the leg and knee

When standing, the leg expends zero energy. “Previously, our robots had to work against the spring or with a motor either when standing or when pulling the leg up, to prevent the leg from colliding with the ground during leg swing. This energy input is not necessary in BirdBot’s legs,” says Badri-Spröwitz and Aghamaleki Sarvestani adds: “Overall, the new robot requires a mere quarter of the energy of its predecessor.”

The treadmill is now switched back on, the robot starts running, and with each leg swing, the foot disengages the leg’s spring. To disengage, the large foot movement slacks the cable and the remaining leg joints swing loosely. This transition of states, between standing and leg swing, is provided in most robots by a motor at the joint. And a sensor sends a signal to a controller, which turns the robot’s motors on and off. “Previously, motors were switched depending on whether the leg was in the swing or stance phase. Now the foot takes over this function in the walking machine, mechanically switching between stance and swing. We only need one motor at the hip joint and one motor to bend the knee in the swing phase. We leave leg spring engagement and disengagement to the bird-inspired mechanics. This is robust, fast, and energy-efficient,” says Badri-Spröwitz.

Monica Daley observed in several of her earlier biology studies that the bird’s leg structure not only saves energy during walking and standing but is also adapted by nature so that the animal hardly stumbles and injures itself. In experiments with guineafowls running over hidden potholes, she quantified the birds’ remarkable locomotion robustness. A morphological intelligence is built into the system that allows the animal to act quickly – without having to think about it. Daley had shown that the animals control their legs during locomotion not only with the help of the nervous system. If an obstacle unexpectedly lies in the way, it is not always the animal’s sense of touch or sight that comes into play.

“The structure with its multi-jointed muscle-tendons and its unique foot movement can explain why even heavy, large birds run so quickly, robustly, and energy-efficient. If I assume that everything in the bird is based on sensing and action, and the animal steps onto an unexpected obstacle, the animal might not be able to react quickly enough. Perception and sensing, even the transmission of the stimuli, and the reaction cost time,” Daley says.

Yet Daley’s work on running birds over 20 years demonstrates that birds respond more rapidly than the nervous system allows, indicating mechanical contributions to control. Now that the team developed BirdBot, which is a physical model that directly demonstrates how these mechanisms work, it all makes more sense: the leg switches mechanically if there is a bump in the ground. The switch happens immediately and without time delay. Like birds, the robot features high locomotion robustness.

Whether it’s on the scale of a Tyrannosaurus Rex or a small quail, or a small or large robotic leg. Theoretically, meter-high legs can now be implemented to carry robots with the weight of several tons, that walk around with little power input.

The knowledge gained through BirdBot developed at the Dynamic Locomotion Group and the University of California, Irvine, leads to new insights about animals, which are adapted by evolution. Robots allow testing and sometimes confirming hypotheses from Biology, and advancing both fields.

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• PAPER – BirdBot achieves energy-efficient gait with minimal control using avian-inspired leg clutching. Alexander Badri-Spröwitz, Alborz Aghamaleki Sarvestani, Metin Sitti and Monica A. Daley. Science Robotics, Vol 7, Issue 64. DOI: 10.1126/scirobotics.abg4055

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