Insect-scale robots can squeeze into places their larger counterparts can’t, like deep into a collapsed building to search for survivors after an earthquake.
However, as they move through the rubble, tiny crawling robots might encounter tall obstacles they can’t climb over or slanted surfaces they will slide down. While aerial robots could avoid these hazards, the amount of energy required for flight would severely limit how far the robot can travel into the wreckage before it needs to return to base and recharge.
To get the best of both locomotion methods, MIT researchers developed a hopping robot that can leap over tall obstacles and jump across slanted or uneven surfaces, while using far less energy than an aerial robot.
The hopping robot, which is smaller than a human thumb and weighs less than a paperclip, has a springy leg that propels it off the ground, and four flapping-wing modules that give it lift and control its orientation.
Here is an exclusive Tech Briefs interview — edited for length and clarity — with Co-Lead Author Yi-Hsuan “Nemo” Hsiao, an MIT graduate student, and Senior Author Pakpong Chirarattananon, Associate Professor, City University of Hong Kong.
Tech Briefs: What was the biggest technical challenge you faced while developing this robot?
Hsiao: One of the biggest challenges is our robot is still connected with a power cable. That power cable is really hard to model; like when the robot is jumping around with those cables, we'll be pulling the robot. We cannot really simulate this and that is actually causing most of the failing cases. I think going into power autonomy — which means we carry a battery and a sensor onboard — will be the next step. And this robot has really opened the opportunities for us to do that.
Tech Briefs: The article I read stated, “Moving forward, the researchers plan to leverage its ability to carry heavy loads by installing battery sensors and other circuits onto the robot in the hopes of enabling it to hop autonomously outside the lab.” Do you have any set plans for that future research, work, etc.?
Hsiao: I'm personally not too much involved in this project, but many of my colleagues are currently working on the flying version. They work with other groups to customize the batteries, and they're working on the customized circuit, trying to boost up the batteries. Let’s say, usually batteries are about 3.7 volts. They’re trying to boost it up to about 500 volts for our actuator to work. We also need to customize the wing and the artificial muscle so that everything can work together. So, that’s an active research direction.
Tech Briefs: Can you please explain in simple terms how it works?
Chirarattananon: To give you a bit of background — and to answer your question about the biggest challenge — hopping is actually a little bit trickier than how it looks or how it seems, because how are you going to take off, right? And, the direction where you're going to go actually depends on how you land. It depends on the exact orientation or the altitude of when you land and where you’re going to end up in the next step. So, if you don't plan very well, one day you can fall or crash. This is why Nemo brought up the fact that having the tether or the cable pulling the robot could mess up how this works.
Because, if we cannot compensate for that disturbance, then we cannot guarantee that it's going to work and it's not going to crash. So, in this sense, that basically is the kind of source of the difficulty.
To explain how this robot works, a little bit is related to that in a way that is different from flying. When we are hopping, we actually are not actuating or operating the robot all the time; we have a very brief period where we actually apply power to the robot, and that's when we have to do all the work for controlling the trajectory of where the robot is going to be in the subsequent flight phase or when the robot is in the air. So, basically, most of the time the robot is in free fall. We only have a brief period where we can have some control over what the robot is doing.
Hsiao: An interesting characteristic is, because of the single leg, our robot can hop on multiple terrains very easily. We don't need to change the control parameters, and, not only on the flatter terrain, it can also hop on incline terrain. So, that pretty much covers most of the outside-the-lab environments because you can imagine everything is either grassy or rocky, like an incline. And, because of the light weight, it can hop on even the floating lotus leaf or on another flight robot.
Tech Briefs: Is there anything else you'd like to add that I didn't touch upon?
Hsiao: I think this research, particularly, reduces the power required to operate by like 64 percent and also increases payload by about 10 times. So, at one end we already need less power and on top of that we have a lot more payload to put on electronics, battery, those types of things.
We were originally thinking power autonomy could happen in one or two years or even three. Now, we’re kind of seeing it happening in, probably, one year. We will probably see one version of the robot like hopping autonomously in the lab. We're not saying it will go out of the lab yet, but probably in a year or so we'll start to see things happening.
Chirarattananon: I think that that's actually the main excitement around the next steps. In the meantime, this kind of hopping or the commotion has shown potential for larger robots as well and we believe it scales rather well. For example, in nature, you see animals such as rabbits and kangaroos that hop and are very different in size. So, we can potentially build different devices or vehicles this small or also larger up to, for example, human scale, that can use a similar commotion and that can also be an emerging direction in addition to traditional or conventional major robots such as humanoids .
Hsiao: One last thing to add is, because our robot has a really tiny moment of inertia, it can actually do really low-height jumping. So, this allows our robot to operate in really confined spaces. Let's say you have a horizontal pipeline in the diameter of three inches; it’s really hard for traditional territorial robots to go inside and hop around. It's like doing really finesse locomotion. But our robot can hop in a really low altitude, so it can actually operate in a really confined space without too much of a problem.
Transcript
00:00:00 [MUSIC PLAYING] NARRATOR: Insect scale robots have size on their side, allowing them to squeeze into places that larger counterparts can't. However, tiny, crawling robots might encounter obstacles on the ground they cannot overcome, and while aerial robots can avoid these hazards, the amount of energy required for flight could limit how far they can travel before needing to recharge. Offering an alternative, a team of researchers at MIT
00:00:27 has developed a hopping robot that can leap over obstacles and jump across slanted or uneven surfaces, while using far less energy than an aerial robot of comparable size. This hopping robot, which is smaller than a human thumb and weighing less than a paperclip, has a springy leg that propels it off the ground and four flapping wings that give it lift and control its orientation. The robot can jump up to four times its height
00:00:54 and has no trouble hopping across ice, wet surfaces, and uneven soil. The key to the hopping robot's performance is a fast control mechanism that determines how the robot should be oriented for its next jump. Sensing is performed using an external motion tracking system, and an algorithm computes the necessary control information using sensor measurements. As the robot hops, it arcs in the air. At the peak of this arc, it estimates its landing point.
00:01:23 Based on this target landing point, the controller calculates the desired takeoff velocity for the next jump. Meanwhile, the robot flaps its wings to adjust its orientation, ensuring it strikes the ground at the correct angle and axis to move in the proper direction and at the right speed. The researchers tested the hopping robot and its control mechanism on a variety of surfaces. It successfully traversed all of them,
00:01:46 including a surface that was dynamically tilting. Since the controller can handle multiple terrains, the robot can easily transition from one surface to another, and due to its small size and light weight, the robot has an even smaller moment of inertia, which makes it more agile and better able to withstand collisions. Moving forward, the researchers plan to install batteries, sensors, and other circuits directly onto the robot in the hope of enabling it to hop
00:02:12 autonomously outside the lab.
