# Field Navigation Using Fuzzy Elevation Maps Built with Local 3D Laser Scans
## 2 The Mobile Robot Andabata  
Andabata is an outdoor mobile robot that weighs 41 kg and is powered by batteries. The maximum dimensions of the robot are 0.67 m long, 0.54 m wide and 0.81 m high (see Figure 1).  
Andabata consists of a skid-steered vehicle with four 20 cm diameter wheels. Each wheel has a passive suspension system (with two springs and a linear guide with a stroke of 6.5 cm) and is actuated by its own direct-current motor with an encoder and a gearbox. The motors are driven by two dual Sabertooth power stages connected to two dual Kangaroo controllers. These controllers receive speed commands for the left and right treads and send motor encoder measurements via an USB port to the  
Figure 1: The Andabata mobile robot with the 3D laser scanner on top.  
computer (see Figure 2). The maximum speed of the vehicle is \(v_{max}=0.68\,\mathrm{m}\,\mathrm{s}^{-1}\) during straight line motion, but decreases to zero as the turning radius reduces.  
The chassis of the robot has three levels: bottom for the motors and the battery, middle for electronics and the computer, and top for sensors and a WiFi router (see Figure 1). The computer has an Intel Core processor i7 4771 (four cores, 3.5 GHz, 8 MB cache) and 16 GB RAM. A tablet is used for remote supervision and teleoperation of the robot via the onboard WiFi router (see Figure 2). Andabata has a smartphone to obtain data from its GPS (with a horizontal resolution of 10 m), inclinometers, gyroscopes, magnetometers and its camera.  
In addition, the robot has a 3D laser rangefinder (see Figure 1), built from a two-dimensional (2D) scanner Hokuyo UTM-30 LX-EW [28]. Power and data transmission between the base and the head is carried out by a slip ring that allows unconstrained rotation. The range of measurements varies from 0.1 m to 30 m (reduced to 15 m with direct sunlight). The 3D sensor has the same vertical resolution of the 2D scanner (i.e., 0.25\({}^{\circ}\)). The horizontal resolution can be selected by modifying the rotation speed of the head. The blind zone of the 2D sensor is 90\({}^{\circ}\), which is located below to avoid interferences with the robot. Thus, the blind zone for the 3D laser rangefinder is a cone with the radius of the base equal to the height \(h=0.723\,\mathrm{m}\) of its optic centre above the floor.  
Andabata can be teleoperated by a person through an Android app in the tablet called Andabata, which is an adaptation of the Mover-bot app [30] that runs both on the tablet and the onboard smartphone. The application on the tablet has two sliders for both hands to indicate the speed of the left and right treads, which are sent through the local WiFi network to the Andabata app on the smartphone (see Figure 3). Video feedback, GPS position, and robot inclination is provided by the smartphone to the tablet via WiFi. Another app on the smartphone, called Android_sensors_driver, publishes a ROS topic directly on the computer with all the sensory data of the smartphone via WiFi [31].  
Figure 2: Communication between hardware components of Andabata.  
Figure 4 shows a general scheme of the ROS nodes employed by Andabata. The Navigation_mode node selects tread commands from teleoperation or from autonomous navigation, which are sent to the motor drivers through the Motor_control node. During teleoperation, the Andabata app on the smartphone retransmits the speed commands from the tablet to the Teleoperation node via USB. The rest of ROS nodes are explained in the following sections.