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; ...

Design, fabrication and control of soft robots

“…1g) generates pressurized gas using a hydrogen peroxide monopropellant 56 . Combustible fuels are another promising high energy density chemical fuel source 57,58 .…”

“…Soft robotics projects have also explored quadrupedal locomotion 29,10 , rolling 28,73 , and snake-like undulation 8 . Jumping has also been achieved using internal combustion of hydrocarbon fuels to achieve rapid energy release 57,58 .…”

A 3D printed monolithic soft gripper with adjustable stiffness

“…internal). Pneumatic [14,17] or hydraulic actuation [18], tendon cable driven by an electric motor [16], more recently combustion power [19] are external actuation methods used in soft robots. Conducting electroactive polymers [20], dielectric elastomers [21], hydrogels [22], shape memory alloys [12] belong to the secondary actuation method are partially or fully incorporated within the structure of a soft robot.…”

Propulsion-Based Soft Robotic Actuation

“…To date, this technology has matured and is ubiquitous in our daily lives, and can be found in jet planes, factory air compressors, gas powered pistons and so on. The working mechanism behind air propulsion lies in the creation of kinetic motion through directional exertion of pressurized air either through combustion or an air reservoir [2]. Although air propulsion generates bending in soft flexible bodies during motion as an inevitable effect [3][4][5], there has been minimal investigation done into the use of air propulsion to create soft body locomotion to perform tasks.…”