Design, control, modeling, and locomotion analysis of a multi-legged modular miniature robot with soft backbones

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Özcan, Onur
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Bilkent University
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Soft Modular Legged roBot (SMoLBot) is a legged, foldable, modular, miniature robot with soft backbones. SMoLBot’s body and locomotion mechanisms are folded out of acetate sheets and its compliant connection mechanisms are molded from Polydimethylsiloxane (PDMS). High maneuverability and smooth walking pattern can be achieved in miniature robots if high stiffness kinematic parts are connected with compliant components, providing the robot structural compliance and better adaptability to different surfaces. SMoLBot is exploiting features from origami-inspired robots and soft robots, such as low weight and low cost foldable rigid structures and adaptable soft connection mechanisms made of PDMS. Every single module in SMoLBot is actuated and controlled by two separate DC motors, that enable gait modification and a higher degree of freedom on controlling the motion and body undulation of the robot in turning and rough terrain locomotion. Each module has 44.5 mm width, 16.75 mm length, and 15 mm height, which is approximately the same size as two DC motors and a Li-Po battery. The dynamic formulation of SMoLBot is obtained using Newton-Euler formulation and it depends on the physical parameters of the contact and closed-chain kinematic analysis of the feet. The dynamic model framework is proposed by determining the dynamic locomotion parameters of each module as an individual system, as well as, considering the dynamics of the whole robot; i.e. the robot is modeled as one system and modules are considered to be set of flexible links connected to each other, within this system. Kinematic constraints among these modules are obtained by considering the types of backbones integrated in the robot. Various types of backbones are used within the experiments that are classified into two groups: rigid, and compliant backbones. Experimental results of SMoLBot running/walking with different symmetrical and asymmetrical gates validate the dynamic model presented in this thesis. Additional to the dynamic model, the effect of the backbone stiffness on the locomotion of the legged miniature modular robots with multiple numbers of modules is studied. Analyses comparing the velocity of SMoLBot with different numbers of modules and different types of backbones are presented using the proposed dynamic model. The results indicate that there is an optimum torsional stiffness of the backbone for a legged miniature modular robot that maximizes the robot’s translational velocity. Additionally, we can show that, for a given backbone stiffness or a specific range of compliance between the modules, there is an optimum number of feet for the miniature robots. Furthermore, in this thesis, a locomotion study that investigates the motion patterns of the running/walking multi-legged modular miniature robots with soft module connections, is conducted. The locomotion study is done using the presented dynamic model and results are verified using SMoLBot. The optimum feet sequence and the optimum stride length of a multi-legged robot are derived using the locomotion analyses, and the dynamic and kinematic formulations. The optimum gait analysis of the multi-legged SMoLBots represents different but unique feet contact sequence patterns for each robot with a different module number and diverse ranges of compliance between the modules. Furthermore, analysis considering the effect of various feet failure cases on the locomotion of a multilegged robot with soft/rigid backbones, is conducted. This study investigates the locomotion behavior of a legged miniature robot with different combinations of the non-functioning feet. Additionally, a case-sensitivity study of an n-legged SMoLBot’s locomotion on its individual modules during the operation, is also conducted. This study investigates the modular robot’s locomotion with multiple different failure cases where each particular case only considers the effect of an individual module failure on the overall motion of the robot, while the gate is not altered.

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