Using Explosions to Power a Soft Robot

Abstract

This manuscript describes the use of explosions to power a soft robot-one composed solely of organic elastomers (e.g., silicones). The robot has three pneumatic actuators (pneu-nets) in a tripedal configuration. Explosion of a stoichiometric mixture of methane and oxygen within the microchannels making up the actuators produced hot gas that rapidly inflated the pneu-nets, and caused the robot to launch itself vertically from a flat surface (e.g., to jump). A soft flap embedded in the pneu-net acted as the valve of a passive exhaust system, and allowed multiple sequential actuations. The flame and temperature increase from the explosions are short-lived, and do not noticeably damage the robots over dozens of actuation cycles.1 Soft robots have emerged as a new set of machines capable of manipulation [1][2][3][4] and locomotion. [5][6][7][8] Pneumatic expansion of a network of microchannels (pneu-nets) fabricated in organic elastomers, using low-pressure air (<10 psi; 0.7 atm; 71 kPa), provides a simple method of achieving complex movements: [1, 5] grasping and walking. Despite their advantages (simplicity of fabrication, actuation, and control; low cost; light weight), pneu-nets have the disadvantage that actuation using them is slow, in part because the viscosity of air limits the rate at which the gas can be delivered through tubes to fill and expand the microchannels. Here we demonstrate the rapid actuation of pneu-nets using a chemical reaction (the combustion of methane) to generate explosive bursts of pressure.Although the combustion of hydrocarbons is ubiquitous in the actuation of hard systems (e.g., in the metal cylinder of a diesel or spark-ignited engine [9]), it has not been used to power soft machines. Here, we demonstrate that explosive chemical reactions [10] producing pulses of high temperature gas for pneu-net actuation provides simple, rapid, co-located power generation, and enables motion, in soft robots. In particular, we used the explosive combustion of hydrocarbons triggered by an electrical spark to cause a soft robot to "jump" (a gait previously only demonstrated for hard systems [11][12][13][14][15][16]).We fabricated a tripedal robot ( Fig. 1; Fig. S4) using soft lithography.[1] This robot incorporated a passive valving system (Fig. 1a, inset) that allowed us to (i) pressurize the pneunets easily, (ii) exhaust the product gases automatically (without external control), and (iii) actuate the same pneu-net repeatedly. By actuating all three legs simultaneously, we caused the robot to jump more than 30 times its height in less than 0.2 s, at a maximum vertical velocity of ~3.6 m/s. 2Our choice of explosive chemical reactions for actuation was based on several factors, one being their high volumetric energy density (in units of MJ/L). The energy density of a compressed gas, which we previously used to power soft robots, is ~0.1 MJ/L at 2,900 psi from the potential for mechanical work, w, done by the change in pressure (P), and volume (V) when decompressed to atmospheric pressure; ...

Pneumatic Networks for Soft Robotics that Actuate Rapidly

“…Soft robots are machines fabricated from compliant materials (polymers [1][2][3][4][5][6][7][8] , elastomers [1] , hydrogels [9,10] , granules [11] ); they can operate with several different modes of actuation (i.e., pneumatic [1,5,[11][12][13] , electrical [7,[14][15][16][17][18] , chemical [12,19,20] ), and their motion can be either fast (>1 Hz) [9,12,14] or slow (<0.1 Hz) [1,21] .…”

“…Exploration of rapid motion in soft robotics is just beginning, and examples are at a level of initial demonstrations [1,9,12,14] . For example, the "GoQBot" developed by Trimmer et al, is a worm-like robot that performs a single rapid actuation (<100 ms) to achieve a ballistic rolling motion by using the deformation of coils of shape-memory alloy (SMA) [14] .…”

Flexing into motion: A locomotion mechanism for soft robots

“…To establish the criteria for stability for the solution θ = θ * , we compute the second variation J of the potential energy function V in (23). Omitting details as they can easily be deduced from [27,28], we find that…”

“…While we do not specify on the precise mechanism by which the intrinsic curvature is changed, there has been an increased interest in the development of mechanisms for changing κ 0 in components of soft robots. The interested reader is referred to [22,23,24,25,26] for examples of these mechanisms.…”

Soft hands: An analysis of some gripping mechanisms in soft robot design

“…Our modeling and analysis work builds on the earlier papers Majidi et al (2012Majidi et al ( , 2013a; Zhou et al (2015) While we do not discuss the precise mechanism by which the intrinsic curvature is changed, there has been an increased interest in the development of mechanisms for changing κ 0 in components of soft robots. The interested reader is referred to Galloway et al (2013); Shepherd et al (2013); Suzumori et al (2007); Takashima et al (2011);Wakimoto et al (2009) for examples of these mechanisms. Also, in order to make the theoretical model more tractable for analysis, we only examine gripping mechanisms that involve point contact with an object.…”