# Tensegrity Applications to Architecture, Engineering and Robotics: A Review
## 4 Robots and Electromechanical Engineering
### Rolling Robots  
When it comes to rolling tensegrity robots, most of the examples will be about six-strut tensegrity robots (expanded cuboctahedrons), due to their spherical shape. One of the first rolling tensegrity robots was proposed by [PERSON] et al. [83]. This robot was built of 6 rigid struts and 24 pneumatic McKibben actuators, working as tensional elements (Figure 26a). Their motion principle was once again based on the ability of tensegrity structures to reach stable states. They applied pressure using the actuators to shrink it, forcing the imbalance, which will force the structure to roll into another stable state.  
Figure 25: Tensegrity robot proposed by [PERSON] and [PERSON] [81].  
Other rolling tensegrity robots based on the same motion were proposed by [PERSON] et al. [84]; in this case, the actuation method used an artificial muscle fibre made up from a liquid crystal elastomer (LCE)-carbon nanotube (CNT) composite that can generate large and reversible light-actuated deformation, and thus enables light-powered motion of the tensegrity robot. The proposed robot for this task is shown in Figure 26b.  
Probably one of the most iconic rolling tensegrity robots that we must mention is the Super Ball v2 [71,87]. This robot was the second version of a robot built for the NASA project together with Dynamic Tensegrity Robotics Lab (DTRL). This project intended to explore the concept of a \"tensegrity rover which may self unpack from long term storage, survive the impact of landing on a planetary body, and locomote to science locations once on unknown terrain\". The first version [85] of the rover was a six-bar icosahedron (Figure 26c), which succeeded in showcasing a large-scale tensegrity robot built for locomotion. The objective of creating a second-generation prototype was to withstand impacts on a much larger scale, while also focusing on meeting other design priorities such as having a two-meter actuation stroke, reliable force sensing, low-friction, low wear cable routing, and the ability to actuate all 24 cables within the prototype. Additionally, the goal was to achieve a system mass of under 40 kg (Figure 26e). As mentioned before, the symmetrical spherical shape of the tensegrity icosahedron makes it advantageous for rolling movement. In addition, the tensegrity icosahedra can be folded into a flat star configuration, as shown in Figure 26d, which is interesting for future space exploration because of reduced mission payload expenses.  
Figure 26: (**a**) Prototype of 6-strut tensegrity robot proposed by [PERSON] and [PERSON] [83]. (**b**) Rolling robot proposed by [PERSON] [84] (Image courtesy of [PERSON]). (**c**) Super Ball v1 [85]. (**d**) Super Ball v2 deployed. (**e**) NASA robots—left: ReCTeR, right: modular tensegrity platform. (Images courtesy of NASA) (**f**) Robot proposed by [PERSON] (image courtesy of [PERSON]) [86].  
The actuation method proposed for the Super Ball v2 was a steerable locomotion controller; they validated their design by proving it capable of moving in specific trajectories and navigate around obstacles [88].  
Several methods for controlling the direction in which the robot rolls were also proposed by different authors: analytic based on finite elements [89] or a path planning based on an A\({}^{\star}\) modified algorithm [90].  
Another way of rolling was proposed by [PERSON] et al. [86]. They introduced a new way of motion in which they used a six-strut tensegrity structure where the tensile elements were springs. The robot was actuated by vibration motors (Figure 26f). They designed the structure to maximize its resonant possibilities, and they made it roll into different positions just by vibrating it at specific frequencies.  
All these examples of tensegrity robots haven shown good response to movement in difficult terrains such as sand, pebbles or small rocks, which would make them suitable for space exploration in other planets or satellites.