For a 10-mm-long robot, as shown in fig. S9 (A and B), we observed noticeable motion even under an AC drive voltage as low as 8 V peak to peak (movie S6), which is a relatively low voltage requirement among insect-scale piezoelectric actuators (45).
The attached video demonstrates the locomotion of a 10 mm-long prototype in the controlled transparent quartz tube environment. Specifically, the relatively low voltage requirement is demonstrated by the noticeable motion at 8V.
We then fabricated prototype robots with different lengths ranging from 10 to 30 mm at an interval of 5 mm using the map of λ/L and β/π of 0.1 and 0.4 for guidance.
The authors chose to test different lengths of robots to find which length was most efficient for movement. They began at 10mm and moved up 5mm till they reached 30mm. This yielded 5 tests of different length robots. Given the results in Fig. 3, the 10mm robot was deemed most efficient in locomotion.
humidity
Shin et al, Lee et al, and Ma et al. have chosen to harness environmental humidity as the energy source for their robots. However, these robots have a limited speed of 6mm/s.
crawling robots
Rafsanjani et al. utilized Japanese paper folding techniques to create a soft robot mimicking the crawling motion of a snake. Similarly, Wang et al. employed inchworm movement patterns in their soft robots.
The relatively fast locomotion and robustness are attributed to the curved unimorph piezoelectric structure with large amplitude vibration, which advances beyond other methods.
The authors determined that the rapid locomotion and robustness of the soft robot are due to the unique structure and materials used to construct it along with the large deformation that the robot undergoes upon actuation.
An opposite trend exists for soft robots, as shown in the elliptical and blue color shaded area, which suggests that the relative speed increases as the body mass increases (19) except for recent robots driven by an external magnetic force (26–28).
In soft robots, speed increases as body mass increases with the exception of robots using magnetic force actuation.
We found that the values of λ/L and β/π near 0.1 and 0.4, respectively, resulted in robots with the fastest running speeds.
The authors performed 25 tests to determine what combination of relative leg position and angle would offer the fastest running speeds of the soft robot. Given Fig. 3B, a position at 0.1 and angle of 0.4 was determined to result in the fastest speed.
Although some soft robots driven by magnetic fields, humidity, or heat or light sources can have fast instantaneous running speeds, slow responses and a bulky setup to generate the external power, such as the magnetic field, are among the limitations.
Next Generation Science Standards Disciplinary Core Idea ETS1.B: Developing Possible Solutions
"The creative process of developing a new design to solve a problem is a central element of engineering." (page 206). Various actuation methods have been designed and tested to ensuring the fast motion of this soft robot
24. S.-J. Park, M. Gazzola, K. S. Park, S. Park, V. Di Santo, E. L. Blevins, J. U. Lind, P. H. Campbell, S. Dauth, A. K. Capulli, F. S. Pasqualini, S. Ahn, A. Cho, H. Yuan, B. M. Maoz, R. Vijaykumar, J.-W. Choi, K. Deisseroth, G. V. Lauder, L. Mahadevan, K. K. Parker, Phototactic guidance of a tissue-engineered soft-robotic ray. Science 353, 158–162 (2016).
Park et al. created a biohybrid system that enables an artificial animal to swim with light stimulation. The device was inspired by batoids (like sting rays), where the researchers reverse-engineered the animal’s musculoskeletal structure and used optical signals to enable steering and turning maneuvers.
We observed that a large percentage of aerial duty cycles were required to generate fast running speeds for the robot.
The authors used a high-speed camera to characterize the duty cycles of the soft robot. They concluded that the soft robot achieves the fastest speed when it spends most of its time in the air (maximizing the aerial duty cycle).
magnetic force
Prior studies conducted by Vogtmann et al, Hu et al, and Pierre et al. have embedded permanent magnets into the soft robot that allow for the generation of a magnetic field.
This actuation method allows for faster movement, but the robot developed by Hu et al has a top speed (213 mm/s) that is still one-fourth of the robot presented in this work.
sturdiness of cockroaches
Constructing Evidence and Designing Solutions (SEP6):
The engineers designed a soft robot by mimicking principles of animal locomotion such as speed, utility and sturdiness.
However, small-size arthropods outperform larger animals in terms of their relative moving speeds.
Crosscutting Concepts: Scale, Proportion, and Quantity
It is important to recognize the correlation between different speed and energy measurements with changes in scale and proportion. Here, an arthropod will outperform a larger animal in terms of moving speed (expressed in body length per unit time) due to its small size.
The scaling trend from the tested robots shows that miniaturization with higher resonant frequencies could further increase the relative speeds, but precision fabrication, the requirement of powering wires, and untethered operations could be the key challenges in pursuing smaller-scale robots.
Common Core State Standards English Language Arts-Literacy: Key Ideas and Details: RST.11-12.1.
The authors discuss the pros and cons of miniaturizing a robot to make it faster.
Driving signals (frequency, amplitude, or phase) of the two domains are controlled independently so that each of them allows different ground reaction forces to turn in the desired direction.
In the future, a light-weight battery can be integrated into the soft robot, allowing for independent movement without attached electrical wires.
Read the article here: https://www.futurity.org/roach-sized-robot-biomimicry-2122002-2/
23. M. Rogóż, H. Zeng, C. Xuan, D. S. Wiersma, P. Wasylczyk, Light-driven soft robot mimics caterpillar locomotion in natural scale. Adv. Optic. Mater. 4, 1689–1694 (2016).
Rogóz et al. utilizes liquid crystalline elastomers that change shape under light; specifically, a continuous wave green laser beam scans the robot body and a traveling deformation is observed. The robot can perform difficult tasks like walk up a slope and squeeze through a narrow slit, however it is hindered by damage from burning along the laser beam center.
22. E. Wang, M. S. Desai, S.-W. Lee, Light-controlled graphene-elastin composite hydrogel actuators. Nano Lett. 13, 2826–2830 (2013).
Wang et al. chooses to use light-driven hydrogel as it allows for wires and electrodes to be avoided, and light can be controlled more easily than other actuation methods. However, the crawling gait was generated by curling and uncurling after exposure to a near infrared laser. This mechanism poses issues due to the constant laser repetition required to move the device.
13. N. Kagawa, H. Kazerooni, Biomimetic small walking machine, in Proceedings of the 2001 IEEE/ IEEE/ASME International Conference on Advanced Intelligent Mechatronics, Como, Italy, 8 to 12 July 2001 (IEEE, 2001).
In order to mimic a hop-like pattern, Kagawa et al. have used the movement style and foot path of cockroaches. Unlike the single-leg and later implemented double-leg utilized in this paper, Kagawa uses a four-legged walking machine with dimensions of 2 in x 1 in (50.8 mm x 25.4) which is significantly larger than this 10 mm x 15 mm soft robot.
8. W. Wang, J.-Y. Lee, H. Rodrigue, S.-H. Song, W.-S. Chu, S.-H. Ahn, Locomotion of inchworm-inspired robot made of smart soft composite (SSC). Bioinspir. Biomim. 9, 046006 (2014).
Wang et al. employed worm movement patterns to show proper movement of their soft robots. Specifically the looping gait, requires front and back leg anchoring for sequential contracting and stretching. This differs from the four main postures used in this wave-like gait pattern which include aerial, front-touching, back-touching, and both-touching.
In this case, a 10-mm-long prototype (0.024 g) robot was used to achieve a relative running speed up to 20 BL/s driven near its resonant frequency at 850 Hz. In comparison, under driving frequencies of 800 and 900 Hz, lower relative running speeds of 13 and 3.6 BL/s were recorded, respectively (movie S3).
The attached video demonstrates the locomotion of a 10 mm-long prototype in the controlled transparent quartz tube environment. Three different driving frequencies were used to help characterize the relationship between driving frequency and robot speed.
Experimentally, the robustness of the prototype soft robot was demonstrated by applying a 100-g mass (1500 times its own body weight) with little change in its speed after the mass was removed, as shown in movie S7. Moreover, the soft robot could continue to function (one-half of the original speed) after being stepped on by an adult human (59.5 kg), a load about 1 million times its own body weight (Fig. 5, A to C, and movie S7).
The first 20 seconds of the attached video demonstrate the robustness of the soft robot in two different circumstances. We find that the device continues to function after the application of a 100-g mass, as well as after being stepped on.
To further increase the running speed, we added and attached a back leg to a 3 cm–by–5 cm prototype robot to emulate galloping-like gaits (movie S8).
The attached video demonstrates a new type of movement pattern, galloping, where back legs have been attached to the device.
With the more effective galloping-like gait mechanism, a two-legged robot achieved a running speed about three times that of a one-legged 3 cm–by–1.5 cm robot under similar driving conditions, as shown in movie S9.
The attached video provides a comparison of the one-legged robot with the new galloping two-legged robot, with the latter traveling at three times the prior.
One simple way to turn would be to assemble two separated electrical domains, as shown in figs. S13 and S14 and movie S10.
The attached video demonstrates the ability for the soft robot to turn, specifically through the use of two electrical domains.
The slope climbing capability of the robot is demonstrated in movie S7, in which the robot reached 7 BL/s while climbing a slope with an angle of 7.5° (Fig. 5D) and 1 BL/s while climbing a slope with an angle of 15.6° (Fig. 5E). Our soft prototype robot could also carry loads equal to the weight of a peanut (0.406 g) (Fig. 5, F and G).
The last 10 seconds of the attached video demonstrate device robustness in 2 circumstances. The robot successfully climbs inclined surfaces and carries a peanut.
Using a prototype robot of 10 mm (length) by 15 mm (width) by 3 mm (height) as an example, we first selected 25 combinations (Fig. 3B, gray dots) of the above geometric parameters to fabricate prototypes and conducted experiments to plot the normalized running speed map as a function of relative leg position (λ/L) and relative leg angle (β/π) in Fig. 3B.
The authors chose to test different angles for the device curvature to optimize speed for efficient movement. Specifically, the relative leg position (λ/L) and angle (β/π) were varied between 0.1-0.5 and 0.1-0.7 respectively.
We observed that if the applied load is below 100 g, then the robot can recover back to the original shape and maintain greater than 88% of its original speed. As the applied load increased, the moving speed decreased.
Here, the authors quantify the robustness of their device. The use of PVDF, PET, and silicon allows for the soft robot to maintain its shape. However, excess weight is shown to damage the structure of the device, resulting in decreased speed.
duty cycles
Fraction of time spent in each phase of one cycle of the motion.
Again, we note that although the morphology and motion of our robot do not mimic any specific animal, small runners, such as cockroaches (41) and desert ants (44), also use aerial phases to attain their fastest speeds.
Constructing Evidence and Designing Solutions (SEP6):
The knowledge that arthropods use the aerial phase to achieve high speeds was leveraged in order to ensure the fast movement of this soft robot.
Galloping is used by some rapid running mammals, where back bending increases stride length and allows the recovery of stored elastic energy (63)
Crosscutting Concepts: Structure and Function
The movement patterns exhibited by the hind legs of certain mammals, like horses, have aided in their high running speeds.
we introduce a fast and ultrarobust insect-scale soft robot for potential applications in environmental exploration
Next Generation Science Standards Disciplinary Core Idea ETS2.B: Influence of Engineering, Technology, and Science on Society and the Natural World
"How do science, engineering, and the technologies that result from them affect the ways in which people live? How do they affect the natural world?" (page 212)
information reconnaissance
Military term for gathering information about an enemy for combat intelligence.
gait
A pattern of limb movement, where the gallop, commonly seen in horses, is the one of the fastest gait that can be performed.
light
Light can be easily controlled with high resolution and light-based mechanisms have been used in order to avoid potentially invasive wires or electrodes, Wang et al. chooses to use light-driven hydrogel; Rogóz ̇ et al. utilizes liquid crystalline elastomers that change shape under light; Park et al. uses tissue engineering principles to engineer cells that respond to light cues. Still, these prior publications are unable to achieve speeds greater than 3.2 mm/s.
two-segment mass-spring model
This idealized model allows for the characterization of motion animals use, like bouncing. Specifically, it is assumed that the movement behaves like a mass bouncing on a spring.
piezoelectric effect
The ability of the PVDF to generate an electric charge in response to the applied voltage, resulting in expansion (or stretching) and contraction (or shrinking).
pin joint
A connection between two rigid bodies that allows only relative rotation about a single direction.
polymeric materials
Polymers are materials made of long, repeating chains of subunits called monomers. Examples include plastics, proteins and DNA.
hopping robots
In order to mimic a hop-like pattern, Kagawa et al. have used the movement style and foot path of cockroaches. On a larger scale, researchers like Haldane et al. have chosen a small primate, galagos, as their model animal which is known for having the highest vertical jumping ability.
Mobility
The ability to move freely and easily
animal locomotion
A variety of methods that animals use to move from one place to another.