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====== The Capo Robot ====== | ====== The Capo Robot ====== | ||
- | {{:wiki:robot:4wd1-robot-aluminum-kit.jpg?nolink|}} | + | Designed mobile platform is composed of the following |
+ | components: | ||
+ | - chassis, | ||
+ | - power supply | ||
+ | - control unit, | ||
+ | - motor drivers, | ||
+ | - sensors and other peripherals. | ||
+ | Selected chassis is a Lynxmotion A4WD1 four-wheel body, | ||
+ | 30 cm long and wide. The platform is shown in figure 1. | ||
+ | |||
+ | {{:wiki:robot:capos.png?nolink&600|}} | ||
+ | |||
+ | Fig. 1. Designed robotic platform based on A4WD1 chassis. | ||
+ | |||
+ | Power is supplied by two LiPo batteries connected in | ||
+ | parallel with the nominal voltage level 14.8 V and single | ||
+ | battery capacity 5000mAh, which is sufficient for several hours | ||
+ | of continuous operation. Once the robot runs out of energy, | ||
+ | batteries can be replaced without restarting the control unit. | ||
+ | |||
+ | The main robot control unit is Pandaboard. Pandboard | ||
+ | is a low-power low-cost single board computer based on the | ||
+ | OMAP4430 dual core processor. Platform gives access to | ||
+ | many of the powerful features of the multimedia processor | ||
+ | while maintaining low cost. This will allow the user to develop | ||
+ | software and use available peripherals in many configurations. | ||
+ | The major components available on the PandaBoard, which | ||
+ | can be used in the robot, are as follows: | ||
+ | |||
+ | * Power Management Companion Device, | ||
+ | * Audio Companion Device, | ||
+ | * Mobile LPDDR2 SDRAM Memory, | ||
+ | * HDMI Connector, | ||
+ | * SD/SDIO/MMC Media Card Cage, | ||
+ | * UART via RS-232 interface via 9-pin D-Sub Connector, | ||
+ | * LS Research Module 802.11b/g/n, Bluetooth, FM, | ||
+ | * Camera Connector, | ||
+ | * LCD Expansion Connectors, | ||
+ | * Generic Expansion Connectors, | ||
+ | * Composite Video Header. | ||
+ | |||
+ | The device runs Linux kernel with either popular distribution. The most basic task of the Pandaboard is to control the | ||
+ | motor drivers – the RoboClaws | ||
+ | |||
+ | The RoboClaw 2X15 Amp is an extremely efficient, versatile, dual channel synchronous regenerative motor controller. | ||
+ | It supports dual quadrature encoders and can supply two | ||
+ | brushed DC motors with 15 amps per channel continuous and | ||
+ | 30 amp peak. With support for dual quadrature decoding it | ||
+ | get greater control over speed and velocity is automatically | ||
+ | maintains speed even if load increases. RoboClaw uses PID | ||
+ | calculations with feed forward in combination with external | ||
+ | quadrature encoders to make an accurate control solution. | ||
+ | RoboClaw is easy to control with several built in modes. | ||
+ | It can be controlled from a standard RC receiver/transmitter, | ||
+ | serial device, microcontroller or an analog source, such as a | ||
+ | potentiometer based joystick. | ||
+ | |||
+ | To control the speed of motor RoboClaw uses pulse width | ||
+ | modulation (PWM). Pulse width modulation is a method | ||
+ | of adjusting the current or voltage signals, which consists | ||
+ | of changing the pulse width of constant amplitude, used in | ||
+ | amplifiers, switching power supplies and systems control the | ||
+ | operation of electric motors. PWM powers the system directly | ||
+ | or through a low pass filter which smoothes the voltage | ||
+ | waveform or current. | ||
+ | |||
+ | Because the Pandaboard and the RoboClaw works with | ||
+ | different logic levels, a converter is required. For this purpose | ||
+ | KAmodLVC logic level converter has been used. KAmod-LVC module is an 8-bit bi-directional converted voltage levels. | ||
+ | The converter can be used to connect two digital systems | ||
+ | operating with different voltages (like 1.8V and 5.0V in this | ||
+ | case). | ||
+ | |||
+ | The basic orientation sensors embedded in the robot includes a gyroscope, accelerometer and magnetometer. The | ||
+ | sensor can be used to determine the position of the robot in two | ||
+ | planes. The diagram of components connections and relations | ||
+ | is presented in Fig 2. The alignment of the components in the | ||
+ | chassis is shown in Fig 3. | ||
+ | |||
+ | {{:wiki:robot:robot-uklasd-elementow.png?nolink&300|}} | ||
+ | |||
+ | Fig. 2. The block diagram of the robot components. | ||
+ | |||
+ | |||
+ | {{:wiki:robot:robot-3d.png?nolink&300|}} | ||
+ | |||
+ | Fig. 3. Internal design of the robot components. | ||
+ | |||
+ | |||
+ | The central point of control and communication is the | ||
+ | Pandaboard. This board has several communication interfaces which are to control the robot effectors and to collect | ||
+ | information from the sensors. Communication bus between | ||
+ | Pandaboard and motor controller was realized using RS232 | ||
+ | interface. For the purpose of control only lines RxD and | ||
+ | TxD are used. There is no hardware flow control, because | ||
+ | communication with the Pandaboard and RoboClaw is realized | ||
+ | in inquiry respond method and it is always initiated by the | ||
+ | Pandaboard. Therefore, if the control program waits for data | ||
+ | from the controller it is not necessary to control rate. The data | ||
+ | rate of this link is set to 38400bps. | ||
+ | |||
+ | |||
+ | The orientation sensor uses serial I2C bus. To communicate | ||
+ | with this bus the system uses duplex line Serial Data Line | ||
+ | (SDA) and one-way line Serial Clock Line (SCL). Both lines | ||
+ | are pull-up to power line so it is easy to detect transmissions | ||
+ | collision using hardware. In robotic system this bus combines | ||
+ | simplicity and functionality in one at a low investment of | ||
+ | hardware and software to give the desired effect. | ||
+ | |||
+ | |||
+ | Robot communication with the surrounding environment is | ||
+ | based on the built-in wireless card: Pandaboard WiFi. Each | ||
+ | robot has its own unique MAC address so it is possible to | ||
+ | communicate with the selected robot even if a group of robots | ||
+ | is working in the same network. | ||
+ | |||
+ | Robot design provides an easy way for extending the range | ||
+ | of sensors or effectors. It has been tested with ultrasonic sensors, laser rangefinders, cameras and Microsoft Kinect sensor. | ||
+ | Further extensions are possible using various interfaces: USB, | ||
+ | COM, I2C or SPI. | ||
+ | |||
+ | To determine the exact position of the robot can use the | ||
+ | Global Positioning System (GPS) receiver or the more accurate indoor marker-based Hagisonic Stargazer system. | ||
+ | Stargazer uses markers placed on the ceiling and on the basis | ||
+ | of their positions it can determine the location of the robot | ||
+ | with high accuracy. Another localization technique uses Hokuyo laser scanner and particle filter algorithm. | ||
+ | |||
+ | Twenty units have been built in the course of the project for testing and further | ||
+ | development purposes. The cost of all parts for a single unit | ||
+ | does not exceed 900 USD, which is a very low price for the | ||
+ | capabilities. The robot can develop speed of 3 m/s, it can put | ||
+ | itself into vertical position by climbing a wall. It includes an | ||
+ | on-board computer with 2-core CPU, running ordinary Linux | ||
+ | OS and providing large variety of extension ports. It meets | ||
+ | all defined requirements for testing the planned applications. | ||
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