# A Mobile Robot with Omnidirectional Tracks--Design and Experimental Research
## 2 Materials and Methods  
### Construction of a Mobile Robot with Multidirectional Tracks  
A classical vehicle with a track drive system (excavator, bulldozer, tank, armoured personnel carrier, bomb disposal robot, etc.) is made of a body and two continuous track systems located symmetrically to the body (Figure 2a). A vehicle with a drive system with multidirectional tracks is equipped with four continuous track systems, which can usually be positioned in various ways with regards to the vehicle's body. The typical schemes of continuous track positions encompass tracks that are completely overlapping (Figure 2b), tracks that are partially overlapping (Figure 2c), as well as systems with non-overlapping tracks (Figure 2d). It was assumed that the mobile robot to be constructed would have the structure of a symmetrical system with completely overlapping tracks, i.e., it will be made of a body and four parallel track drive systems of equal length with completely overlapping tracks (Figure 2b). During contact between the continuous track and the surface, tractive force is generated. This force is necessary for a vehicle to move. A large surface-track contact area and an appropriately adjusted track preload result in a lower unit pressure of the track when compared to the wheel. A standard, single continuous track system is made of a track located between the drive wheels, idler, road wheels and return rollers (Figure 3a). In some track vehicles (e.g., excavators), there are solutions in which the drive wheels and idlers also take the load-carrying capacity (Figure 3b). This type of powertrain was also selected for the designed mobile robot. However, due to the large radius of the drive wheels and idlers in relation to their spacing, no extra road wheels were used (Figure 3c). Tracks in the continuous track system are composed of a closed sequence of several dozen links that are connected to one another with rotating pairs. In the case of multidirectional tracks, each link is equipped with an additional rotating roller positioned at angle \(\gamma\) (usually \(30^{\circ}<\gamma<60^{\circ}\)) to the link axis. The view of a single link with length \(a\), width \(b\), and height \(h\), and also a cylindrical roller with radius \(r_{r}\), is presented in Figure 4.  
The designed mobile robot is equipped with four independent continuous track systems with multidirectional tracks that have only drive wheels and idlers. It is a four-degrees-of-freedom system. The drive is transferred from the rotating drives to the drive wheels using belts. In the middle part of the robot's body, at point \(R\), the local x'y' coordinate system is located. The kinematic scheme of the robot is shown in Figure 5.  
Figure 2: Schemes of track positions with two and four continuous tracks: (**a**) symmetrical system, (**b**) symmetrical system with completely overlapping tracks, (**c**) system with partially overlapping tracks, (**d**) system with non-overlapping tracks. It was assumed that the designed robot would be used indoors (residential buildings, offices, warehouse facilities, production halls, etc.). Therefore, its dimensions must be adapted to overcome the typical obstacles seen in such places: doors, thresholds, staircases, etc. The robot should move at a maximum speed of \(v_{R}\) = 0.2 m/s, which is the speed considered acceptable for a robot moving in a 'human environment' [35]. This means that the maximum track speeds 1, 2, 3, 4:  
\[v_{R}=v_{1}=v_{2}=v_{3}=v_{4} \tag{1}\]  
The resulting basic dimensions are described in Table 1.  
Figure 4: View of a single multidirectional track link: 1—link, 2—roller. Figure 3: Continuous track system: (**a**) standard system, (**b**) system with drive road wheels, idlers and road wheels, (**c**) system with drive road wheels and idlers without road wheels. Figure 6 shows an overview of the developed solid model of the robot and the detailed views of the solid model of the track system.