Browsing by Author "Mahkam, Nima"

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Open Access
Control and study of bio-inspired quadrupedal gaits on an underactuated miniature robot
(Institute of Physics, 2023-01-25) Askari, Mohammad; Uğur, Mustafa; Mahkam, Nima; Yeldan, Alper; Özcan, Onur
This paper presents a linear quadratic Gaussian (LQG) controller for controlling the gait of a miniature, foldable quadruped robot with individually actuated and controlled legs (MinIAQ-III). The controller is implemented on a palm-size robot made by folding an acetate sheet. MinIAQ-III has four DC motors for actuation and four rotary sensors for feedback. It is one of the few untethered robots on a miniature scale capable of working with different gaits with the help of its individually-actuated legs and the developed controller. The presented LQG controller controls each leg’s positions and rotational speeds by measuring the positions and estimating the rotational speeds, respectively. With the precise gait control on the robot, we demonstrate different gaits inspired by quadrupeds in nature and compare the simulation and experiment results for some of the gaits. An extensive simulation environment developed for robot dynamics helps us to predict the locomotion behavior of the robot in various environments. The match between the simulation and the experiment results shows that the proposed LQG controller can successfully control the miniature robot’s gaits. We also conduct a case study that shows the potential to use the simulation to achieve different robot behavior. In a case study, we present our robot performing a prancing similar to horses. We use the simulation environment to find the required motor configuration phases and physical parameters, which can make our robot prance. After finding the parameters in simulation, we replicate the configuration in our robot and observe the robot making the same moves as the simulation. © 2023 IOP Publishing Ltd.
Open Access
Design, control, modeling, and locomotion analysis of a multi-legged modular miniature robot with soft backbones
(2020-07) Mahkam, Nima
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.
Open Access
Effect of feet failure and control uncertainties on the locomotion of multi-legged miniature robots
(Institute of Electrical and Electronics Engineers, 2022-03-09) Mahkam, Nima; Uğur, Mustafa; Özcan, Onur
This study investigates the effects of control uncertainties and random feet failures on the locomotion of the multi-legged miniature robots. The locomotion analyses results are verified with our modular multi-legged miniature robot with a soft/hybrid body named SMoLBot. A single SMoLBot module is 44.5 mm wide, 16.75 mm long, and 15 mm high with two individually actuated and controlled DC motors. This individual actuation makes it feasible to run with any imaginable gait, making SMoLBot a nice candidate for gait study analyses. The presented locomotion study shows that the effects of control uncertainties and feet failures are highly dependent on the total number of legs and the type of backbone attached to the robot, e.g., increasing the total number of legs or utilizing a rigid backbone on the robot helps the robot to walk faster compared to similar robots with soft backbones or the ones with fewer modules. This study presents a guide to the researchers on the effects of feet failures and control uncertainties on the locomotion of soft/hybrid multi-legged miniature robots.
Open Access
A framework for dynamic modeling of legged modular miniature robots with soft backbones
(Elsevier, 2021-06-29) Mahkam, Nima; Özcan, Onur
In this work, the dynamics of ”n” legged modular miniature robots with a soft body is modeled. The dynamic formulation is obtained using Newton–Euler formulation that depends on the contact parameters and the feet closed-chain kinematic analysis. The dynamic model determines the locomotion parameters of each module as an individual system as well as the dynamics of the whole robot in a 3D space; i.e., the robot is modeled as one system, and modules are considered to be sets of flexible links connected within this system. Kinematic constraints among these modules are obtained by considering the type of backbone integrated into the modular robot. Various types of backbones are used that are classified into three groups: rigid, only torsional, and soft. The model is verified using SMoLBot, an origami-inspired miniature robot made of multiple modules and soft/rigid backbones. Additional to the dynamic model, the effect of different sets of design parameters on the locomotion of the legged soft-bodied modular miniature robots is studied. Analyses comparing the velocity of SMoLBot with a different number of modules and various types of backbones are presented using the proposed dynamic model. Our results show the existence of an optimum backbone torsional stiffness for legged miniature modular robots and an optimum number of legs for a given backbone stiffness that maximizes the robot’s velocity. In this research, presented results and locomotion study show that the robot’s design should be iteratively improved based on specific optimum goals for exclusively defined task to satisfy the operational needs.
Open Access
Gait and locomotion analysis of a soft-hybrid multilegged modular miniature robot
(Institute of Physics Publishing Ltd., 2021-09-28) Mahkam, Nima; Özcan, Onur
The locomotion performance of the current legged miniature robots remains inferior compared to even the most simple insects. The inferiority has led researchers to utilize biological principles and control in their designs, often resulting in improved performance and robot capabilities. Additionally, optimizing the locomotion patterns compatible with the robot's limitations (such as the gaits achievable by the robot) improves the performance significantly and results in a robot operating with its maximum capabilities. This paper studies the locomotion characteristics of running/walking n-legged modular miniature robots with soft or rigid module connections. The locomotion study is done using the presented dynamic model, and the results are verified using a legged modular miniature robot with soft and rigid backbones (SMoLBot). The optimum foot contact sequences for an n-legged robot with different compliance values between the modules are derived using the locomotion analyses and the dynamic and kinematic formulations. Our investigations determine unique optimum foot contact sequences for multi-legged robots with different body compliances and module numbers. Locomotion analyses of a multi-legged robot with different backbones operating with optimum gaits show two main motion characteristics; the rigid robots minimize the number of leg-ground contacts to increase velocity, whereas soft-backbone robots use a lift–jump–fall motion sequence to maximize the translational speeds. These two behaviors are similar between different soft-backbone and rigid-backbone robots; however, the optimal foot contact sequences are different and unpredictable.
Open Access
Miniature modular legged robot with compliant backbones
(IEEE, 2020) Mahkam, Nima; Bakır, Alihan; Özcan, Onur
Soft Modular Legged Robot (SMoLBot) is a miniature, foldable, modular, soft-hybrid legged robot with compliant 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 out of PDMS. Each single module in SMoLBot is actuated and controlled by two separate DC motors. This enables gait modification and 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 with two DC motors and a LiPo battery. The comparisons between robots with compliant and rigid backbones demonstrate smoother walking pattern, and approximate decrease in body's roll angle from 12° to 6°, and pitch from 10° to 7°. The independent actuation and control over each leg in n number of modules make SMoLBot an ideal candidate for gait studies. Moreover, the possibility of changing the structural stiffness of the robot with different backbones enables such a compliant modular robot to be used for locomotion optimization studies in miniature scale.
Open Access
Smooth and inclined surface locomotion and obstacle scaling of a C-legged miniature modular robot
(IEEE, 2021-07-12) Mahkam, Nima; Yılmaz, Talip Batuhan; Özcan, Onur
This work investigates the locomotion of a modular C-legged miniature robot with soft or rigid backbones on smooth, rough, and inclined terrain. SMoLBot-C is a C-legged miniature robot with soft or rigid backbones and foldable modules. The robot's climbing capabilities with soft and rigid C-legs and different backbones on rough terrain with obstacles and the robot's mobility on an inclined surface are compared. Our results show that the C-legged robot with soft legs and soft backbones can climb up to a higher obstacle, and walk on surfaces with higher inclination angles compared to the same robot with rigid legs and backbones, regardless of the number of modules (legs). Additionally, a velocity comparison study using SMoLBot-C operating at two different gaits is conducted. The results show that the robot with soft legs and compliant-I backbones operating with trot gait possesses the highest velocity compared to the other robots with similar leg numbers. Moreover, the effect of a compliant tail on the robot's locomotion on smooth and rough terrains is investigated, where the results show that the robot with the compliant tail is capable of walking on surfaces with higher inclination angles compared to the same robot without a tail. Furthermore, adding a tail to the two-legged SMoLBot-C doubles the maximum scalable obstacle height; the robot with a tail can climb up an obstacle 2 times higher than a module's height. Locomotion analysis in this manuscript provides a better insight into C-legged miniature robots' locomotion with soft or rigid legs while the modular connections' structural stiffness varies from rigid to soft.