**Abstract**

3D printing technology enables the design and testing of highly complex robot prototypes and joints. Here an original idea for a walking robot is presented, based on a minimalist approach. Although the robot has a simple mechanical structure using only 2 motors, it can walk, turn around its central axis and climb high obstacles. The simple design ensures higher reliability in terms of mechanics and control. A design principle is suggested, which minimizes power consumption during climbing. The kinematics and static conditions for overcoming an obstacle are analyzed and the movements of the robot are simulated. A 3D-printed prototype of the robot is created. It is used for experiments to test the efficiency of different materials and shapes for the robot's feet when climbing. The results are ranked and compared with the efficiency of other walking robots.

**Keywords:** Walking robot, Robot design, Overcoming an obstacle, 3D print, Minimalist approach

## **1. Introduction**

Walking robots are designed to move in an environment with multiple and diverse obstacles [1]. For that reason they need to do complex coordinated motions, which require a complex mechanical structure and advanced control system with multiple sensors [2]. Mobile robots, created to conduct rescue operations or inspection tasks in an urban environment, often face problems when they need to climb stairs [3]. As opposed to wheel robots, walking robots have a more complex design, more motors and are slower [1, 3]. Often, they have more degrees of freedom and use special algorithms. The advantage is that the robot can do complex movements [1, 4]. However, this comes at the price of more components in the design. Hence, the disadvantages:


The following questions arise: What would be the simplest walking robot design that can effectively overcome obstacles? What would be the minimal number of degrees of freedom for such a robot? Can a simple control system work when overcoming different types of obstacles? How can 3D printing technology bring additional advantages in the development of robots, based on minimalist approach?

**2. Simple mechanical design**

*DOI: http://dx.doi.org/10.5772/intechopen.97335*

*3D Printed Walking Robot Based on a Minimalist Approach*

It is well known that a robot needs at least 6 degrees of freedom to reach any point in its workspace with any orientation. 3 for changing the position and 3 for realizing the random orientation. Since the walking robot moves on a surface, it can be concluded that 3 degrees of freedom are enough - X, Y axis and orientation. After all there are examples of mobile robots with two motors that achieve satisfactory results 1. A new simple design of a two-motored robot, called "Big Foot", is suggested.

The robot's body is made up of a round base {1} and a platform {2} in which all the main elements are located. The platform is mounted in the center of the circular base, and the two bodies can rotate relative to each other around the vertical axis R1 (see **Figure 1**). The movement around R1 is realized by means of a controlled motor {6}. The stator of this motor is fixed on the platform {2}, and the rotor is connected by means of a reducer to the base {1}. The motor {7} is located in the platform {2} and drives the shaft {8} by means of a gear mechanism. This shaft performs the second important rotation R2, which is perpendicular to R1. Two arms {3} are fixed to the shaft {8}, and two feet {4} are mounted at the ends of the arms. For proper walking, the feet {4} and the round base {1} need to move with a constant orientation with respect to each other. To achieve this, a gear mechanism {5} is used, which has a gear ratio of 1. It consists of 3 gears with the same module and number of teeth which are mounted in the arm {3} (Figur 1) The 3D printed model is powered by a rechargeable battery, and the control is carried out remotely via Bluetooth communication with a PC or a smartphone. Different variants of the control software are developed using sensors of different types. Video with the robots movements is available from: Video 1. The key elements for walking are the body {2}, arms {3} and feet {4}. This is the basic structure of the robot. While walking, the body and feet remain parallel **Figure 2**. Initially the body {2} is fixed (**Figure 2a**). The arm {3} is rotating and thanks to the gears z1, z2, z3 the feet are moving parallel to the fixed body before reaching the ground. Afterwards, the feet {4} are fixed (**Figure 2b**), the arm {3} is rotating and this time the body {2} is in motion, remaining parallel to the feet. The trajectories

The trajectory of any edge point of gear z2 is interesting. The trajectory resembles a heart and is called the cardioid - a type of cycloid. It can be followed in the

The rotation mechanism is presented in **Figure 3**. Here the gear motor {6} works in a mode where the rotor is fixed and the body rotates as the stator operates. Thus

the robot can rotate to any angle without any of the wires tangling up.

can be seen in the following videos: Video 2 and Video 3.

*Structure of the big foot robot and a picture of the 3D printed prototype.*

animation: Video 4.

**Figure 1.**

**95**

The stability of a walking robot is a major issue, because it defines the conditions under which it will not lose balance. There are two types of stability - static and dynamic. Static walking means that the robot can be stopped at any moment during the gait cycle without losing balance. Dynamic walking means that additional internal movements and algorithms are needed to sustain balance.

Two-legged robots usually have dynamic stability and a relatively large number of degrees of freedom [5–7]. They can go around or climb obstacles, but need a complex control system and consume a lot of energy. Their reliability is lower, due to the large number of electrical and mechanical components. There are experimental two-legged robots which can sustain static balance.

Alternative design solutions with a minimum number of mechanical elements [8] and nature-inspired robots are being sought [9]. In [10] is presented an ultralight, inexpensive two-legged robot "SLIDER" with a design of the leg without a knee. This non-anthropomorphic design with straight legs reduces the weight of the legs significantly, while maintaining the same functionality as anthropomorphic legs. The robot has 8 degrees of freedom, four for each leg.

The four-legged 3D printed robot presented in [9] is 3D printed with PLA (polylactic acid). It has a simple design and can walk without any form of software or controller. The robot consists of a rectangular body and four legs, each with a degree of freedom that rotates and raises the leg. At the end of each of the legs is mounted a rubber foot to improve traction. Although there are only 4 degrees of freedom, the robot realizes a gait which is similar to the gaits used by walking primates and cattle (grazing animals).

In [8] is presented a robot with one motor and several clutches. By sequential action of the clutches, the proposed robot can rotate in different directions and can walk. It can be combined with other identical modules to build more complex reconfigurable robots.

Walking mechanisms that do not need motors are studied [11, 12]. However, their passive movement is realized only on slopes and is difficult to control.

3D printing technology is used to create and test the qualities of prototypes of walking robots [9, 10, 13, 14]. Conventional materials such as PLA [9] and ABS (Acrylonitrile Butadiene Styrene) [13] are most commonly used. In [14] a methodology for 3D printing of hermetic soft drives with built-in air couplings is proposed. Two materials are used, hard and flexible, and printing is done with a printer with two extruders. Additive manufacturing is evolving and finds more and more applications in robotics. In [15] the main focus is on developing a methodology for creating a 3D printed, low-budget robotic arm with six degrees of freedom that can be used with an external artificial intelligence system. In [16] is used a custom 3D printer and CAD model of a structure for a specialized device, which consists of two-layer micro actuators driven by hydrogels.

Maintaining stability when moving [17, 18] and overcoming obstacles [2, 19] are also important issues that have been studied in recent years.

For these reasons, here it will be discussed the design of a new 3D printed model of a walking robot, based on a minimalist approach [20, 21]. Mies van der Rohe's motto "Less is more" reflects the approach to the robot's design. Using only two motors, the robot can walk forward and backward, rotate 360 deg. around itself and overcome obstacles including climbing stairs.
