**6. Results from experiments with the 3D printed model**

Although the 3D printed model is only a prototype, it can be used for experiments and useful conclusions can be drawn. 3D printing enables us to easily create and adjust prototypes. Already known key advantages of this technology are:


Different versions of Big Foot were created. The first prototype used shafts with small diameters and with very small diameters and the transmission of torque is achieved by friction forces (**Figure 10** above). This leads to higher tension on the joints in the shafts and they have a tendency to slip.

important for the proper functioning of the walking mechanism. The shape changes gradually from a reuleaux triangle to a circle. Such objects can be drawn using CAD products and can afterwards be 3D printed. The elements are held by a screw joint. To increase the max obstacle height, the shapes of the feet and the body's base (**Figure 10** pos. 9–10) are changed. The front jigged areas increase the traction and "pull" the robot, while the back edges are rounded which aids the "sliding". As there is no limit for the complexity of the 3D printed feet, the components can resemble

**Figure 11** shows an analogy between a walrus and Big Foot when climbing. The movements share many common characteristics. A comparison with a walrus was

nature more closely.

*Structural changes to big foot.*

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

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

**Figure 10.**

**105**

In the second prototype (**Figure 10** below) some of the problems are solved. The feet shape is improved to secure better traction when overcoming obstacles. To avoid the shafts slipping, their diameter and contact surface is increased. A pin coupling is used (**Figure 10**, pos. 7), which is much more reliable, but leads to stress concentration. An innovative and patented coupling is successfully applied for the joint at point A, where the tension is highest [22] (**Figure 10** pos. 8a). It combines reliability of the contour joints with low levels of stress concentration. This coupling has the advantage to fix the foot to the shaft with constant orientation, which is

*3D Printed Walking Robot Based on a Minimalist Approach DOI: http://dx.doi.org/10.5772/intechopen.97335*

ground or between the feet and the obstacle. At this stage, it is good to ensure good traction between the feet and the obstacle, which will allow the robot to

2.The first stage ends when the feet are simultaneously in contact with both the obstacle and the terrain. The arm {3} rotates and moves the robot body. In this case, the feet are usually stationary, but for high obstacles, it is possible

3.The round base of the robot has reached the obstacle. Due to the movement of the arm {3} a situation is reached in which the base is in contact with the obstacle and the feet in contact with the ground. The robot performs a planer movement in which there is sliding of the feet, the base or both on the terrain

4.A configuration is reached in which the round base is in contact with both the terrain and the obstacle. The arms {3} rotate and they move the feet.

These stages are described in detail in [20, 21], where simulations and results of

Although the 3D printed model is only a prototype, it can be used for experiments and useful conclusions can be drawn. 3D printing enables us to easily create and adjust prototypes. Already known key advantages of this technology are:

• Opportunity to create components with different density and internal infill

• Mixing multiple materials with different characteristics in the production of

Different versions of Big Foot were created. The first prototype used shafts with small diameters and with very small diameters and the transmission of torque is achieved by friction forces (**Figure 10** above). This leads to higher tension on the

In the second prototype (**Figure 10** below) some of the problems are solved. The feet shape is improved to secure better traction when overcoming obstacles. To avoid the shafts slipping, their diameter and contact surface is increased. A pin coupling is used (**Figure 10**, pos. 7), which is much more reliable, but leads to stress concentration. An innovative and patented coupling is successfully applied for the joint at point A, where the tension is highest [22] (**Figure 10** pos. 8a). It combines reliability of the contour joints with low levels of stress concentration. This coupling has the advantage to fix the foot to the shaft with constant orientation, which is

5.The center of gravity of the robot changes, shifting towards the obstacle. Depending on the height of the obstacle, the shape and the materials of the base, the masses of the links and the feet, it is possible to rotate point C around

the edge of the obstacle in order to overcome the obstacle.

**6. Results from experiments with the 3D printed model**

• Opportunity to create very complex external and internal areas

the same element (only with multi material printers).

joints in the shafts and they have a tendency to slip.

pull itself towards it.

*Collaborative and Humanoid Robots*

slipping to occur.

and the obstacle.

various experiments are presented.

structure

**104**

**Figure 10.** *Structural changes to big foot.*

important for the proper functioning of the walking mechanism. The shape changes gradually from a reuleaux triangle to a circle. Such objects can be drawn using CAD products and can afterwards be 3D printed. The elements are held by a screw joint. To increase the max obstacle height, the shapes of the feet and the body's base (**Figure 10** pos. 9–10) are changed. The front jigged areas increase the traction and "pull" the robot, while the back edges are rounded which aids the "sliding". As there is no limit for the complexity of the 3D printed feet, the components can resemble nature more closely.

**Figure 11** shows an analogy between a walrus and Big Foot when climbing. The movements share many common characteristics. A comparison with a walrus was

**7. Conclusion**

the future.

An original design of a 3D printed walking robot based on minimalistic approach is presented. This idea is intended to inspire the design of useful robot structures in

It is considered a design principle and determination of the proportions of the

The kinematics of the robot are analyzed and the key stages for walking on flat

The principles of movement are considered and the robot's ability to adapt to obstacles due to the mechanical structure is highlighted. An algorithm is shown for calculating the change in the instantaneous velocity center of one link while the robot is adapting. This is a practical example of applying kinematic methods in robotics. The main dependences for determining the torque loading of the motor when walking are given. The results of a study of the static conditions for overcoming an obstacle and experiments with a 3D printed model are discussed. Detailed studies and simulations are given in [20, 21]. 3D printing gives new opportunities to create

unconventional structures, which can change the way robots are designed.

The results of experiments with different materials and shapes for the feet and the base of the robot are discussed. Thus is detected the maximum height of the obstacle that can be overcome. After additional design changes, this height is increased to 52 [mm]. An index *Kro* is proposed which relates the robot's dimensions

The results for overcoming an obstacle by different types of robots are ranked

It is not easy to give definitive answers to the questions posed in the introduction. However, from the analysis of the literature and the results of this study it can

If the number of degrees of freedom is less than two, the walking robot cannot be controlled to bypass obstacles. The idea proposed in [8] is debatable whether it can be characterized by one degree of freedom as it also uses controllable couplings.

The presented 3D printed model shows that it is possible to overcome obstacles

3D printing technology facilitates the creation of prototypes of the developed robots. It allows easy realization of links with complex shapes and connections between them.

These research findings are supported by the National Scientific Research Fund,

The author is grateful to his colleagues and in particular to PhD Bozhidar Naidenov for their help in creating the prototype, conducting the experiments and

All graphics and video material used are created by the author.

In addition, it is possible to realize the movements only sequentially.

by using a simple control system without sensors and feedback.

links, based on minimizing the energy during walking.

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

terrain and climbing obstacles are given.

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

with the height of the obstacle it can overcome.

using the proposed index.

**Acknowledgements**

supporting this work.

**Other declarations**

**Thanks**

**107**

Project N ДН17/10-12.12.2017.

be noted that:

**Figure 11.** *3D printed feet with a complex shape, inspired by nature.*

chosen because, like the animal, the robot pulls its heavy body on the obstacle with the help of sharp elements in its feet. Unlike perhaps all known animals, Big Foot can rotate its base and arms more than 360 degrees.

By increasing the width of the feet and the area of the round base the robot can walk on soft terrain (sand, snow, marsh) more easily.

Over 100 experiments for overcoming a higher obstacle were conducted. The same prototype was used, where only the feet {4} and the round base {1} were replaced. They were 3D printed and had different shapes. Two materials were used: PLA (Polylactic acid - most popular for 3D printing) and the flexible FIlaFLEX. The highest obstacle of 43 [mm] which was overcome can be seen here: Video 6; A detailed description of the results is available in [21]. After adding a "tail" to improve the balance of Big Foot, the maximum height was increased to 52 [mm]: Video 7; which corresponds to a coefficient *Kro =* 0.41, see formula 8.

Experiments to overcome an obstacle with a maximum height are made with various mobile robots. Based on literary sources, [21, 23] their respective *Kro*indexes are defined and given in **Table 1**.

Using information from the literature, the coefficient Kro can be determined for different mobile robots in **Table 1**. From the considered examples, it is seen that the highest value Kro = 0.41 is associated with the Transformable-wheeled leg robot [21]. The Big Foot robot proposed in the present study has higher values of the Kro index compared to the mobile robot [20] and the humanoid robot NAO. It can be noted that Big Foot manages to overcome this height by using only one of its two motors, while all other robots use several motors.


#### **Table 1.**

*Kro indices of different mobile robots.*
