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Two-Wheeled

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1. IMU Odroid Figure 5 2 Sketch of the Racer with components offering sufficient space for the components and the possibility to change the centre of gravity of the racer The Odroid the MD25 and the two motors with the corresponding wheels are mounted on the board at the bottom of the robot The MPU 9150 is attached at the upper half of the racer the part that is designed like a ladder At this position the IMU detects early and small changes of the inclination angle of the Racer The ladder provides the ability to change the centre of gravity depending on the position of the weight As a weight the battery was used later in the project 39 5 Project After the skeleton of the robot was build the next task began The next task was to install and run Ubuntu on the Odroid Installing a new operating system on the Odroid turned out to be more difficult than expected Firstly the officially supported operating systems are Android versions Instructions to install one of the many Linux distribution are spread over several community portals but most of them turned out to be not working Eventually after trying to install multiple versions of Ubuntu and its variants on the SD card the only working combination was Xubuntu 13 04 for Odroids on the eMMC Finally the Racer was ready to get its components mounted and afterwards the second milestone was reached 5 5 Request Data from the IMU Xubuntu runs on the Odroid the trans
2. The first task is to establish or to close the connection to the 12C interface and to guarantee that only one connection to the I C interface exists To accomplish this the singleton pattern is used The second task is to handle the communication to 12C interface that means to transfer the received byte arrays from the communication logic layer to the USB ISS and to pass the received byte arrays from the interface back to the communication logic layer 34 4 3 Procedure 4 3 Procedure After the program has started the initialisation phase begins In this phase the required objects are initialised The three main task of this phase are to establish the connection to the USB ISS start the internal clock of the IMU and set the configurations of the MD25 and the IMU Afterwards the IMU data is read once to calculate the inclination angle at start time After the initialisation phase has completed successfully the main cycle begins the control cycle The control cycle proceeds as follows the first step of the cycle is to set the speed of the motors depending on the calculated inclination angle The next step is to read the current accelerometer and gyroscope data from the IMU and calculate the current inclination angle with the help of the complementary filter Finally the most important information is printed on the console and afterwards written into the logfiles Now the cycle starts again with setting the motor speed At the end of the
3. at LOW level during the acknowledge pulse If the SDA line stays at HIGH level during the acknowledge pulse the signal will be interpreted as a not acknowledged signal NACK Figure 2 4 Transmission of the byte 10110001 and acknowledgement with ACK 2 1 4 Addressing Devices connected to the 12C bus have either a seven or a ten bit address 7 Bit Addresses With 7 bit addresses it is theoretically possible to connect up to 128 devices but 16 addresses are reserved so only up to 112 devices can be connected to the bus The 7 bit addresses are transferred as bytes This results from the fact that in addition to the 7 bits of the address an eighth bit is transferred This bit indicates whether the master wants to request or transmit data and is transmitted as least significant bit LSB Thus 7 bit addresses should be considered as 8 bit addresses as shown in Figure 2 5 Lx x x x x x x R Figure 2 5 7 bit address R W bit To start a transmission with a device the master sends a start signal and then transmits the address of the 12C bus If a device recognizes the address as it own it will send an acknowledge signal and the data transfer begins 10 Bit Addresses A 10 bit address is transmitted in two separated bytes as shown in Figure 2 6 The first part of the address is stored in the 2 and the 23 bit of the first byte The remaining part of the address is stored in the second byte The 10 bit addresses can be combi
4. 2 2 2 Co om onen 33 Sketeh of the Racer 2 00 en Re BA a Bade een na 37 Sketch of the Racer with components 0 0 000822 eae 39 Raw data of the accelerometer and the gyroscope 2 22 2 2 41 Coordinate system of the IMU 0 0 00 ee 43 Angle between the the xy plane and the gravity vector 44 Angle calculated by the gyroscope data o 45 Accelerometer data in x direction 2 2 22 CE on nn 46 Complementary Dilbert a a 46 1 Introduction The goal of the project is to construct a robot balancing on two wheels similar to a Segway but much smaller The project is separated into two parts the construction of the Racer and the creation of a controller algorithm In the first part of the project the focus lies on the hardware The goal is to control the motors read out the sensor data handle the request and transmission of data via a data bus and finally build up the Racer Based on the progress in the first part of the project the second part is focuses on processing the received data and the development of a controller to prevent the robot from falling over To accomplish this task sensors are needed which can determine the current position and inclination therefore an inertial measurement unit IMU is mounted on the robot The IMU contains an accelerometer that measures the acceleration in x y z direction and a gyroscope that measures the angle velocity The data provided from the two
5. a design pattern which ensures that a class can be only initialized once It is possible to set a global access to this instance This pattern is used whenever it is important to have only one object of a class for example to mange the access to an interface A singleton class is initialized by itself and do not provide the possibility to initialize more instances 24 3 Components 3 1 USB ISS 3 1 1 Overview The USB ISS Devb shown in Figure 3 1 is a multifunction USB communications module It provides an interface between an USB port and several different kinds of bus systems 12C SPI Serial port Analog Input or Digital I O The module offers the ability to switch the operating voltage between 3 3V or to 5V and to supply external circuitry with up to 80mA The USB ISS supports various fixed frequencies between 20khz 1000khz to transmit data via the PC bus In the PC mode the USB ISS always operates as an I C bus master and handle the I C start restart stop sequencing and acknowledge cycle The USB ISS has two LED A green one and a red one The green LED is the power indication and the red LED the reception of valid commands Figure 3 1 USB ISS 3 1 2 Specific Task The USB ISS is the interface to the PC bus and is used in the 100kHz mode It handles the communication among the Odroid X2 the MPU 9150 and the MD25 3 1 3 Presetting The USB ISS provides different 12C modes with different frequencies of transmission To
6. a sample rate of 250Hz The estimation module estimates next system s state and the LQR controller module generates the signals to control the motors 49 6 Comparison to other solutions The last part is the human machine interface and contains two modules the display module and the button module The display module displays relevant informations on a display with a sample rate of 20Hz The button module is responsible for the user interaction for example the start of the controller after pushing the button Procedure After the robot starts up and the initialization is done the sampling module began to read the sensor data Afterwards the data is handed over to the estimation module where the next system s state with the help of a Kalman filter and the sensor data estimated Based on this state the LQR controller module generates a signal to control the motors 6 1 4 Controller To determine the system s states the accelerometer gyroscope and encoder data are needed To calculate the inclination angle the gyroscope signal is integrated and afterwards combined with the inclination angle calculated by the accelerometer data To combine the two angles the complementary filter is used To calculate the inclination angle with the data of the accelerometer the following function is used 6 1 6 arctan2 accel accel where accel and accel are the accelerometer data along the x and z axes To determine the position and speed of
7. communication logic layer and the connection layer Each of these layers has a specific task The communication among the layers is strict hierarchical that means that a layer is only able to communicate with a layer that is directly above or beneath 4 2 1 Main Logic Layer The main logic layer provides the entry point and contains the main cycle of the program The main logic layer has access to the device interface layer and therefore access to the external devices It provides a platform where the data from the external devices can be accessed and contains the controller that processes received data and determines the speed value for the motors 4 2 2 Device Interface Layer The device interface layer is a kind of interface to the external devices It provides methods to interact and configure the external devices It also contains data from the external devices which are accessible by the main logic layer The device interface layer contains no logic 4 2 3 Communication Logic Layer The communication logic layer provides the logic behind the methods of the device interface layer The layer is responsible to create byte array in a way that the I C interface the USB ISS can handle them and pass them to the connection layer It also converts the byte arrays received from the connection layer into the required data type and pass it to the interface layer 4 2 4 Connection Layer The connection layer is written in C and has two main tasks
8. complementary filter the termios library and the singleton pattern The third chapter Components gives an overview of used hardware and the specific tasks in the robot The fourth chapter Software describes the architecture and the procedure of the software The fifth chapter Project describes the process problems and solutions of the Two Wheeled Racer project It begins with the initial situation and ends with the result of the project In the sixth chapter Comparison to other solutions two other approaches of a two wheeled balancing robot are presented and short comparisons to the solution of the Two Wheeled Racer are given The last chapter Conclusion gives a short summary and describes future work 10 2 Background 21 PC T C is a synchronous serial bus and stands for inter integrated circuit spi08 NXP12 Sem Inv It is based on two wires the serial data wire SDA and the serial clock wire SCL Both lines are bi directional which means each device connected to the bus can request or send data Any device connected to the I C bus is attached additionally to a supply voltage and the ground To ensure that only the requesting device receives the data all devices possess a unique address A device connected to the 12C bus can either act as a master or as a slave device The master device generates the required clock signal therefore the 12C bus must have at least one master device connected It is possible to attach multiple dev
9. drift of the gyroscope by the help of the accelerometer To use the complementary filter one needs to determine the current inclination angle from 45 5 Project 15550 15500 15450 15400 15350 15300 H 15250 15200 15150 15100 Accelerometer 0 100 200 300 400 500 600 cycles Figure 5 7 Accelerometer data in x direction complementary filter angle T Complementary Filter angle 700 900 1000 complementary filter T T ee ior Accel eter roscope 1 1 0 100 200 300 400 500 600 cycles cycles Figure 5 8 Complementary filter gyroscope and accelerometer separately These angles are the averaged using different weights as 5 2 0 j 0i a k where j k 1 a the current inclination angle determined by the gyroscope data 8 the current inclination angle determined by the accelerometer data and 0 the actual inclination angle The filter is simple to understand and easy to implement only the weights had to be adjusted therefore the next task was to implement the complementary filter and afterwards adjusting the weights of the two angles After the filter was implemented adjusted and tested the drift of the angle calculated by the complementary filter was removed as shown in Figure 5 8 Thus the complementary filter solved the angle drift problem 46 5 10 PID Controller Setting 5 10 PID Controller Setting The
10. sensors are used to calculate the inclination angle relative to the balancing point of the robot A PID control algorithm processes the calculated inclination angle and regulates the motors of the Racer based on the inclination angle to prevent the robot from falling over The Racer should be easily expandable hence an Odroid X fully fledged single board computer is used This computer is the brain of the robot and uses a Linux operating system All information are collected and processed there To request or transmit data to external devices an I C bus is used The I C bus also provides the ability to upgrade the robot easily because components that support the 12C protocol can be attached to the bus with minimum effort 1 1 Motivation Studying sometimes can be very theoretical and the practical relevance or a platform to test new solutions is missing For this purpose the Two Wheeled Racer project shall provide a platform to enable students to learn and solidify their knowledge by using the Racer as demonstration tool or to test their own ideas 1 2 Outline This document consists of seven chapters starting with the introduction The second chapter Background provides a background knowledge about the used technology It starts with the explanation of commonly used serial bus the SPI and I C bus followed by a description of the PID controller and its components The chapter also provides a short description of the 1 Introduction
11. sleep mode Inv12 In this state the internal clock of the IMU did not work and thus the IMU did not provide any data To wake up the IMU and start the internal clock a specific value must be written to the specific power management register After the program was updated and the internal clock of the IMU was started the application returned values that changed As a result of that the program was extended so that the values of all coordinates were read and monitored The values varied heavily although the IMU did not move therefore it could not be normal measurement noise For this reason the code of the test application was inspected and afterwards decided that the time had come to write a complete new application The reason for that was on the one hand that the source code had grown large and became rather unstructured and on the other hand contained constructions that could cause errors For example the test application did not consider whether a read command failed Therefore it could happen that two values are added even so they are not supposed to be added or variables get assigned wrong values Another problem of the test application was that the test application read the register one by one instead of using a burst read A burst read is a request command that starts reading at a selected register and reads the following registers afterwards A burst read reads as many registers as specified and is supported by the IMU and the MD25 The IMU e
12. switch to the 100kHz mode a write command with the specific register index and value must be send 25 3 Components to the USB ISS after the connection is established This configuration had only to be done once 3 1 4 Procedure Each interaction among the Odroid and an external device goes via the USB ISS The USB ISS converts the received data from byte arrays into 12C bit sequences and transfers it via the bus to the specific device It also converts the received 12C bit sequences from the external devices back to byte arrays so that the program can process them 3 2 MD25 Dual Motor Drive 3 2 1 Overview The MD25 Deva shown in Figure 3 2 is a H bridge dual motor driver and can be used in I C or Serial mode It requires 12V supply voltage to operate and has a integrated 5V regulator to supply external circuitry up to 1A peak or 300mA continuously The module is able to read motor encoders to determine the distance traveled and offers the ability to control the motors independently It has a feature to facilitate the steering and offers the ability to configure the acceleration of the motors The MD25 also provides the ability to read out the voltage of the connected battery and the used power consumption of the motors Similar to the USB ISS it has two LEDs a red LED and a green LED But in this case the red one is the power indication and the green one flashes whenever a valid command was received Hall Sensor Vcc Hall Sens
13. the wheels the encoder is used The robot has two control schemas the first stabilize the robot at its original position that means it tries to hold the position The second tries to stabilize without trying to hold the position that means after pushing the robot rolls forward to stabilize and remain at the position where it stops To accomplish this the LQR controller regulates the motors to stabilize the system The motors are control with the supply voltage this means the higher the voltage the faster the motor rotates 6 1 5 Comparison This approach needs a well founded background knowledge on the one hand to describe the system of the robot mathematically and on the other hand in cybernetics to control the motors based of the current state of the robot The project focused on creating a controller and not on constructing a robot therefore a hardware was used that already worked and is compatible to other components that can be attached to the system Hence there was no need to mind how the hardware was working or how the devices communicating among each other Compare to this solution the controller of the Racer is less complex and no well founded background knowledge in cybernetics were needed but using a PID controller without a 50 6 2 Zilog ZNEO based Self Balancing Robot mathematical system description that control the robot only based on the inclination angle quickly reach its limit The construction of the Racer is m
14. 0 and the specific value to configure the power management After the MPU 9150 receives this command and wrote the received value into the specific register the internal clock starts and the full scale rages of the gyroscope and accelerometer are set to default The default full scale rages of the accelerometer is 2g and of the gyroscope 250dps 3 3 4 Procedure In each cycle the gyroscope and accelerometer data are needed to calculate the current inclination angle Therefore during a cycle the Odroid requests for the gyroscope and accelerometer data by sending two read command The first command reads the data from the accelerometer and the second from the accelerometer 28 3 4 Odroid X2 Micro HDMI MIPI CSI Connector User Switch Resetable Fuse LCD 38 DC Jack Power S W Eu Reset S W nterface 50 pin USB Host x2 Socket Exynos4412 Prime 12 CPU Module gt USB Host x 2 USB Hub Ethernet Audio Codec DCDCG 3V Converter Level Shifter LAN 10 100 Hardkernel KOREA UART 1 8V Console Port Audio Out USB Host x 2 Audio In Figure 3 4 Odroid X2 3 4 Odroid X2 3 4 1 Overview The Odroid X2 Har shown in Figure 3 4 is a single board computer measures 90mm x 94mm and is based on a 1 7GHz Quad Core with 2GB memory The single board computer requires 5v supply voltage with current up to 2A It possesses six USB 2 0 ports a Micro USB port a RJ45 jac
15. 3 1 Overview The MPU 9150 Spa Inv12 Inv shown in Figure 3 3 is an inertial measurement unit It contains a triple axis accelerometer a triple axis gyroscope a triple axis magnetometer and a temperature sensor The module requires a supply voltage between 2 4V and 3 46V and an operational current up to 4 35mA The integrated gyroscope and accelerometer have programmable full scale ranges The full scale range of the gyroscope can be set to 250 500 1000 or 2000 degrees per second dps and the accelerometer to 2g 4g 8g and 16g The magnetometer has a full scale range of 12004 T The MPU 9150 is extremely shock tolerant in fact up to 10 000g 27 3 Components Figure 3 3 MPU 9150 3 3 2 Specific Task The MPU 9150 is connected to the Odroid using the I C bus and the USB ISS and acts as a slave device It provides the gyroscope and accelerometer data to determine the inclination angle 3 3 3 Presetting As described above the MPU 9150 needs supply voltage between 2 4V and 3 46V but is connected to a 5V circuit supplied by the MD25 Therefore a voltage converter is used to transform the supply voltage from 5V to the required 3 3V After each start up of the robot the MPU 9150 is in a sleep state To wake up the MPU 9150 a write command is transferred to the MPU 9150 via the USB ISS and the I C bus This command contains the register index of the power management of the MPU 915
16. Institute of Machine Learning and Robotic Lab University of Stuttgart Universit tsstra e 38 D 70569 Stuttgart Diploma Thesis Nr 3494 Two Wheeled Racer Marcel Dreher Course of Study Software Engineering Examiner Prof Dr rer nat Marc Toussaint Supervisor Prof Dr rer nat Marc Toussaint Commenced July 7 2013 Completed December 6 2013 CR Classification B 7 1 Abstract The following document describes the process problems and solutions of the project Two Wheeled Racer The project focuses on constructing the robot and providing the core communication principles in addition with basic balancing control The single board computer Odroid X is used as a brain for the Racer to process the data received from an accelerometer and a gyroscope and solve the inclination angle problem To reduce the noise of the sensors the data are filtered and combined with the help of a complementary filter A PID control algorithm is running on the Odroid X to react on the inclination angle calculated from the sensor data and to prevent the robot from falling over Two 30 1 gear motors controlled by a MD25 H bridge dual motor drive are used as actuators The data are transferred among the hardware components with the help of the I C protocol Contents 1 Introduction 1 1 1 2 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 1 3 2 3 3 3 4 3 9 3 6 3 7 4 1 4 2 4 3 5 1 5 2 5 3 5 4 9 9 5 6 8 7 Motivations 2 re o
17. Signal To end the data transmission and free the bus again the master has to send a stop signal to inform the other devices The stop signal informs the devices that the transmission has finished According to that the bus is free again and all devices switch into a listening mode and wait for the next start signal Figure 2 3 shows the stop signal the applied voltage of the SDA wire must changes from LOW level to HIGH level while the SCL wire is at the HIGH level SDA SCL Figure 2 3 Stop signal Repeated Start Signal Sometimes it is necessary to send an argument or command before requesting data but sending a stop signal after the transmission of an argument would free the bus and another master is be able to block the bus In order to prevent this the 12C protocol provides a repeated start signal The repeated start signal is equal to the normal start signal with the only difference that the bus is already held by the master Thus the master is able to continue the transmission without freeing the bus in between Acknowledge Signal After a byte is send an acknowledge clock pulse follows In this clock phase the transmitter releases the SDA line that means it stays at HIGH level or changes to it If the receiver 13 2 Background receives the byte successfully it will confirm by sending an acknowledge signal ACK as shown in Figure 2 4 To accomplish this the receiver must pull the SDA line down and hold it stable
18. USB ISS converts the received 38 5 4 Construction of the Racer and installing Ubuntu on the Odroid data into a I C bit sequence and transfers it via the bus to the specific device USB ISS specification Devb has instructions how commands and data must be stored in a byte array to execute a specific task The LEDs of the MD25 and USB ISS flashed consequently both devices received valid commands but sometimes the received data was not correct or did not make sense at all Therefore the motors were connected and the MD25 was supplied by the 12V supply voltage because the missing of these parts could cause the problem As a result of that it turned out that the writing worked properly This follows from the fact that the the application was able to change the speed of the motors but the request of data from the external device caused problems It seemed that the test application which has in the meantime grown large and unstructured caused the problem The problem should be solved when a new application was build However despite all these difficulties the first milestone was reached 5 4 Construction of the Racer and installing Ubuntu on the Odroid The next goal was to build the skeleton of the Racer and to install Ubuntu on the Odroid Therefore the first task was to buy the material and assemble the skeleton of the racer The robot was build as shown in the Figure 5 2 This structure features a simple design while still Front Back
19. a negative value means the robot inclining forward and vice versa Depending on this values the motor is controlled so that the value is close to 0 6 2 5 Comparison This approach is similar to the solution of the Racer project Both approaches use a PID controller that regulates the motors depending on the inclination angle to prevent the racer from falling over but based on data from different sensors The software architecture is in both solution a layer based structure The construction is function oriented and well suited for balancing because of the wide form of the robot provides a certain level stability The two solution are very similar but the construction of the this solution is well suited for balancing but the brain of the Racer is a fully fledged single board computer instead of the microcontroller and provide therefore more possibilities to use 53 7 Conclusion 7 1 Summary The background knowledge of the used technology were given An overview of the used components and the specific task in the Two Wheeled Racer were depicted The architecture and procedure of the software developed during the project were described The Procedure of the project was described with the initial situation and the result Finally two further approaches were briefly presented and compared to the Two Wheeled Racer solution 7 2 Future Work Creating a detailed mathematical model of the Racer to use a more complex controller to control the robo
20. al as based on work of Col07 JR 75 ECM 08 SAS12 The filter acts as low pass filter and high pass filter simultaneously The filter reduces the disadvantages of the accelerometer and the gyroscope The gyroscope provides exact results over short periods but drifts away over a long period However the accelerometer provides imprecise results over a short period but good results over a long period The complementary filter acts on the one hand as a low pass filter to reduce the noise of the accelerometer signal in case of vibration and on the other hand as a high pass filter to reduce the drift of the angle calculated by the gyroscope signals The complementary filter is a simple alternative to the complex Kalman filter because it is easier to understand implement and in some cases generates results almost as good as those created by the Kalman filter SAS12 The formula of the complementary filter for two data sets is 2 6 y t j u t 7 v t where j i 1 and u t v t represents arbitrary input data at certain time t 23 2 Background 2 8 termios The termios h is a C C library for Linux operation systems that provides the possibility to configure the input output and transmission of data via a serial port with another terminal or device The termios library contains the termios struct struct termios tc lag_t c_iflag input flag tcflag_t c_oflag output flag tcflag_t c_cflag control flag tc lag_t c_l
21. and an amplification factor K The 21 2 Background control deviation is calculated from the difference between the reference value RV and the actual value AV at a certain point in time 2 1 e t AV RV The amplification factor determines how strong the controller reacts on control deviations A large amplification factor causes the p controller to react strongly to small deviation The equation of a p controller is 2 2 y t Kp elt 2 4 Integral Controller I controllers Rob13 con12 are proportional to the temporal integral over the control deviations The controllers integrates over the control deviation within a specified period t and multiplies it with an amplification factor K The control variable depends on the time period and the control deviation Small time periods causes the control variable to change faster than large time periods but then the controller tends to hunt and the system can became unstable Integral Controllers regulates until the deviation is completely eliminated but they are not as fast as p controllers This results from the fact that the control variable of an i controller increases slowly because of the integral over the control deviations in contrast to a p controller that reacts instantly on the control deviation The equation of an i controller is 2 3 y t Ki J e t dt 0 2 5 Derivative Element D elements Rob13 con12 reacts on the rate of change of the control deviation and
22. and the Odroid X2 3 6 EMG30 The EMG30 Devc shown in Figure 3 6 is a 30 1 gear motor with a integrated encoder The motor requires 12v supply voltage and current up to 2 5A It has a rated torque of 1 5 a a no load speed of 216 rpm and a rated speed of 170 rpm The integrated encoder counts 360 steps per output shaft turn and can be read by the MD25 30 3 7 Assembly Figure 3 6 EMG30 3 7 Assembly Figure 3 7 shows the Two Wheeled Racer with dimensions 9 5 cm lt gt 49 3 cm Figure 3 7 Two Wheeled Racer 31 4 Software 4 1 Overview The software has been developed using C and C programming language on a Linux based operation system It is designed based on a layered architecture and is strictly hierarchical as shown in Figure 4 1 The software operates in cycles In each cycle the program executes a predefined sequence of operations to attend multiple tasks communicating with external devices processing the received data from external devices creating logfiles with the most important data and controlling the robot to prevent it from falling over Main Logic Layer Device Interface Layer Communication Logic Layer Connection Layer Software Hardware Figure 4 1 Layered architecture 33 4 Software 4 2 Software Architecture The software is constructed based on a layered architecture It consists of four layers the main logic layer the device interface layer the
23. d be used As operating system a Linux based distribution was chosen and C C as programming language The choice of the programming language fell on C C because it is a hardware related programming language For the communication among the Odroid and the external devices an 12C bus was chosen This has two advantages the first is that all devices are able to use the 12C protocol and therefore able to transmit data via the 12C bus The seconds is that the USB ISS is able to handle the 12C start restart stop sequencing and acknowledge cycle 5 3 Interaction with the MD25 via the USB ISS After the general conditions were specified the prototyping phase started The first milestone was to drive the motors and read the voltage of the power source via the MD25 The USB ISS was the first component to handle with because the USB ISS provides the interface between the Odroid and the 12C bus The documentation leaded to the incorrect conclusion that an additional driver for Linux operating systems was needed to use the USB ISS This resulted from the fact that the documentation where only available for Windows operating systems After a while of trying to run the USB ISS with the additional driver it finally turned out that the standard Linux USB driver was sufficient The next step was to establish a connection to the USB ISS and to communicate with it An application with the associated source code Har was found which was able to establish a co
24. d on page 23 Hacker http www hacker motor shop com e vendo php shop hacker amp Sessionld amp a article amp ProdNr 25000331 amp t 28 amp c 5649 amp p 5649 TopFuel LiPo 20C ECO X 5000mAh 8S Last accessed 03 12 2013 Cited on page 30 Hardkernel http hardkernel com main products prdt_info php g_code G135235611947 ODROID X2 Last accessed 03 12 2013 Cited on pages 29 and 38 InvenSense Inc MPU 9150 Product Specification revision 4 0 edition Cited on pages 11 27 and 40 InvenSense Inc MPU 9150 Register Map and Descriptions revision 4 0 edition 2012 Cited on pages 27 and 41 W T H JR A Comparison of Complementary and Kalman Filtering EEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS AES 11 321 325 1975 Cited on page 23 57 Bibliography Kau07 NXP12 Rob13 SAS12 Sem Spa spi08 B Kaufmann Was ist das Singleton Pattern und wie wird es in C implementiert 2007 http fara cs uni potsdam de kaufmann page GenCppFaqs amp faq Singleton Cited on page 24 NXP Semiconductors UM10204 I2C bus specification and user manual v 5 edition 2012 Cited on page 11 Roboternetz http www rn wissen de index php Regelungstechnik Regelung stechnik 2013 Last accessed 03 12 2013 Cited on pages 21 22 and 23 N S N Anjanaparua K S Self Balancing Robot Using Android Phone In International Conference on Advancement in Engineering Studies amp Technology p
25. d to the master but shares the MOST MISO and SCK wire As a result the slaves must have tri state outputs Daisy Chain In the daisy chain configuration see Figure 2 17 all slaves share the SS and the SCK wire In this case all devices connected to the bus are active at the same time but they do not share the MOSI and MISO wire The structure of the Daisy Chain configuration is like a chain the master is connected to the first slave via the MOSI wire the first slave is connected to the next slave via the MISO output to the MOSI input and so on The last slave in the chain is connected with the master via the MOSI output of the slave and the MISO input of the master again In this configuration all devices act together like a large shift register that means the data bytes received during a cycle will be send to the next device during the next cycle 20 2 3 Proportional Controller Master Figure 2 16 4 Wire Single Master Multi Slave Master Slave 1 sc Slave 2 Figure 2 17 Daisy Chain 2 3 Proportional Controller For all p controller Rob13 con12 applies that the control variable y is proportional to the control deviation e From this it follows that the controller reacts on control deviation without any delay but only if a variance between actual value and reference value exists Therefore the p controller is not able to remove the offset completely The control variable depends on the control deviation e
26. d write bit at the LSB position Therefore the given 7 bit binary number had to be shifted one bit left to get the correct address Afterwards the address of the IMU was changed in the application and therefore the MPU 9150 could be found As a result of that the next task was to read out the data of the accelerometer and gyroscope The data of the accelerometer and gyroscope are stored in internal registers of the IMU Each value of the X Y and Z coordinates consist of two 8 bit numbers and form a 16 bit two s complement number therefore two registers must be read and added up afterwards To sum up the bytes the high byte must be shifted eight digits left and added to the low byte To read out the data the test program had to be extended by a method that reads out the high byte and the low byte of the value of a coordinate These bytes then needed to be processed as described above but the return value of the application was always zero 40 5 5 Request Data from the IMU 16000 T T T T aro T 300 T T T T y T 14000 J APA A AT A kalia Ab Aa o ld daa nh 200 4 12000 H 4 100 4 10000 4 8000 4 OF 7 6000 in 100 L 4 4000 4 200 2000 4 300 4 ol 2000 1 1 1 1 1 1 400 1 1 1 0 100 200 300 400 500 600 700 0 100 200 300 400 500 600 700 Figure 5 3 Raw data of the accelerometer and the gyroscope To understand this behaviour more information was needed After start up the IMU is in a kind of
27. e until it was falling over Finally round about 20cm from the top of the racer were removed to reduce weight and to reduce the oscillation when the accumulator was mounted at the bottom This changed the system behaviour and the accumulator had to be placed at a new position where the motors were able to react fast enough and have the power to prevent the robot from falling over while not becoming too unstable Several positions and parameter configurations of the controller were tested and finally a position was found Now the accumulator was attached halfway up of the Racer Tests showed that the robot was able to hold itself up longer than before but the parameter configuration was still not correct To make the adjustment easier the robot was remote controlled via a ssh connection from a different computer in the same network This offered the advantage of adjusting the parameter without connecting a display to the Racer and the possibility to review the logfiles directly after the test runs The logfiles showed that the i component of the PID controller became immense and for this reason the p and d component were not able to compensated the i component when the robot managed it to change the inclination direction and therefore the i component was limited This limitation did not change much at all but shows a further problem The controller regulates the motors based only on the inclination angle This leads to the fact that the motors stopped
28. ee A o e e lol a ol AF e Pl Outline 220 ls o A o Do os Sey ae ha in Background PU ms Proportional Controller Integral Controller Derivative Element PID Controller Complementary Filter tEIMIOS li ote eek Ee Singleton Pattern Components USBAISS 2 3 ed aro nase MD25 Dual Motor Drive MPU 9150 22 Beet ida Odroid X2F 2a ee echt ob ae TopFuel LiPo ECO X 5000 35 EMGIO it Assembly noria E Software Overview cir a Software Architecture Procedure Project Initial Situation 2 2 2 2 Planing Phase Interaction with the MD25 via the USB ISS 2 2 22 nn Construction of the Racer and installing Ubuntu on the Odroid Request Data from the IMU Connected all Devices to the same PC Bus 2 2 Co oo on Put together the Two Wheeled Racer 11 11 17 21 22 22 23 23 24 24 25 25 26 27 29 30 30 31 33 33 34 35 5 8 Calculate the Inclination Angle o e e 5 9 Remove the Angle Drift 2 2 CL on on nn nn 5 10 PID Controller Setting on on nn Dd Result 2 paeen er ee Dan AR de 6 Comparison to other solutions 6 1 Self Balancing Two Wheeled Robot o 000 ee eee 6 2 Zilog ZNEO based Self Balancing Robot 7 Conclusion Tab SUmMmMmary aaa rar de A a ep 12 Future Work aa sn Br ea ea nd nn Ha
29. em depends on how the IMU was mounted to the racer and is shown in Figure 5 4 0000 x Figure 5 4 Coordinate system of the IMU If the IMU does not move the data from the accelerometer represents the gravitational acceleration and points towards the center of the earth It represents a vector that points vertical down To evaluate the inclination angle the normal of the xy plane was calculated and afterwards the angle between the gravity vector and the normal was determined as shown in Figure 5 5 43 5 Project normal of the xy plane So desired angle A gravity vector Figure 5 5 Angle between the the xy plane and the gravity vector The resulted angle was 90 when the racer was vertical upright Hence 90 must be subtracted to get an inclination angle of 0 when the racer is vertical upright Finally the result was multiplied with 1 to determine the front side of the racer Thus the inclination angle is positive when the racer inclined forwards and vice versa Later it turned out that the inclination can also determined by using the formula 5 1 6 arctana accel accelx Now the approach was implemented and some tests were made This approach worked properly but did not work when the racer accelerated or slowed down because in this cases the vector representing the accelerometer data does not point down vertically Therefore another method was needed to determine the inclination angle when the robot is movi
30. erial Clock wire SCK It is possible to connect an arbitrary number of devices to the bus This results from the fact that a device connected to the bus has no specific address as they do for 12C bus The master selects a slave via the SS wire The data transfer on the SPI bus is full duplex which means the master and slave transfer data at the same time SPI does not support a multi master bus Only one master can be connected to the bus The master always initiates the data transmission and provides the clock signal The clock frequency is usually between 10kHz and 100MHz 2 2 2 Connection Establishment To establish a connection to a slave the master configures the clock and selects a slave via the SS wire Normally the SS wire is active at LOW level so the master has to hold the specific SS wire at LOW level during the whole data transfer To guarantee that only one slave communicates with the master most slave devices have tri state outputs Tri state denotes an additional high impedance output signal of a device in addition to the normal LOW and HIGH signals In this state the device behaves like it is not connected to the bus Thus multiple devices can be connected to one wire without influencing each other 2 2 3 Data Transfer After the master configured the clock and selected a slave the data transmission begins As described above the data transfer operates in full duplex mode with the aid of shift registers Therefore any d
31. es that after the arbitration is done only one master owns the bus and transfers data The arbitration can continue for many bits until one master is left The arbitration works as follows several masters start transferring data at the same time As long as they send identical output signals it is not possible to recognize that multiple masters are transmitting at the same time The arbitration takes place as soon as the output signals differentiate from each other A master looses the arbitration when its output is at HIGH level while another master s output is at LOW level As a result of that the master with the HIGH level output stops sending because the level of the SDA line does not corresponds to the output level of itself Thus the master recognizes that another master is also transferring data and switches off the output An example of the arbitration solution is shown in Figure 2 9 The I C protocol does not offer the possibility to set priorities for devices because the control of the bus depends on the bits to transmit Data Master 1 Data Master 2 loses arbitration SDA SCL Figure 2 9 Multi master conflict avoiding 16 2 2 SPI 2 2 SPI 2 2 1 Overview SPI stands for Serial Peripheral Interface and is a synchronous serial bus It is based on the master slave principle and has four wires The Slave Select wire SS the Master Output Salve Input wire MOSI the Master Input Slave Output wire MISO and the S
32. evices connected to the SPI bus must have a internal shift register see Figure 77 With every clock pulse the master shifts a data bit over the MOSI line into the shift register of the slave The slave shifts at the same time a data bit over the MISO line into the shift register of the master The transmission ends after the master free the SS line again 2 2 4 Communication Modes SPI has no official specification therefore it has no specified communication protocol For this reason SPI provides the possibility to switch between four communication modes These 17 2 Background Figure 2 10 Data transfer among two shift registers modes are defined by two parameters The clock polarity CPOL and clock phase CPHA The CPOL determines the clock idle state and the CPHA determines whether the data will be sampled at first or second edge CPOL LOW and CPHA LOW The idle state of the clock is set to LOW level and the data will be sampled at the first edge The first edge is a rising edge therefore the following data will also be sampled at a rising edge see Figure 2 11 MISO Figure 2 11 SPI mode 0 CPOL LOW and CPHA HIGH The idle state of the clock is set to LOW level and the data will be sampled at the second edge The second edge is a falling edge therefore the following data will also be sampled at a falling edge see Figure 2 12 CPOL HIGH and CPHA LOW The idle state of the clock is set t
33. flag local flag cc_t c_cc NCCS special characters The termios struct consists of four 32bit masks for the different flags and an array for the special character sequences which are used as control characters Every struct variable configures another area The c_iflag variable configures how to process the input before the transmission for example convert Carriage Return CR to Newline NL The c_oflag configures how to process data before output such as expand tabs to spaces The c_cflag configures the general control for instance enable the parity check and finally the c_lflag which configures the terminal properties for example enable the line by line transmission The termios library also provides methods to configure the termios struct or to control the transmission It supports two different modes the canonical mode or cooked mode and the non canonical mode or raw mode The canonical mode provides the line by line transmission which means that complete lines are processed A line ends with a control character such as EOL end of line However in the non canonical mode characters are processed one by one and control characters are not processed because they often consists of more than one character The termios library provide many more possibilities to configure the input output the transmission and the terminal itself but here only a rough overview should be given 2 9 Singleton Pattern The Singleton Pattern Kau07 is
34. han a few seconds The first thought was that the motors were not strong enough and reacted too slowly The MD25 provides the ability to configure the acceleration of the motors Therefore the acceleration level was set to maximum However this did not show any improvements To figure out what exactly causes the problem the program code was extended so that more logfiles were created The new logfiles contained the angle the values of the PID controller elements the motor speed the accelerometer data and gyroscope data This data revealed that the calculated angle drifts which means the angle changes even the IMU did not move the IMU This came from the fact that the gyroscope provides exact results over short periods SAS12 but drifts away over a long period as shown in Figure 5 6 Gyroscope angle 21 4 1 1 L 1 1 L 1 1 1 0 100 200 300 400 500 600 700 800 900 1000 cycles Figure 5 6 Angle calculated by the gyroscope data The accelerometer on the other side provides imprecise results over a short period but good results over a long period SAS12 see Figure 5 7 For this reason a solution must be found to fuse the data This solution should combine the strengths and cancel out the weaknesses of the both sensors to determine the current inclination angle without drift One possibility was the complementary filter the complementary filter uses the advantages of the gyroscope and the accelerometer and tries to remove the
35. ices which can act as a master to the I C bus a so called multi master bus But in this case it must be guaranteed that only one master is active at one time or rather act as a master To accomplish this the 12C protocol provides an arbitration solution A device connected to the I C bus can either act as a receiver or as a sender regardless of its role as a master or a slave device but the master device always initiates the data transfer If the bus is free that means no data transmission is in progress the SDA and the SCL wires will be at HIGH level Each clock pulse is going to transfer one bit 2 1 1 Speed The I C bus offers multiple transfer rates e Low Speed Mode 10 kBit s e Standard Mode 100 kBit s e Fast Mode 400 kBit s e High Speed Mode 3 4 MBit s Clock Synchronization If the receiver device requires more time to process the received data than the sender device needs to transfer data the receiver is able to force the sender into a wait state The sender device pauses as long as it takes the receiver to processes the data and get ready for the next transmission To accomplish this the receiver holds the SCL wire at LOW level The transfer 11 2 Background cannot continue until the device frees the SCL wire again A synchronized clock is generated The LOW period determined by the device with the longest clock LOW phase and the HIGH period determined by the device with the shortest clock HIGH phase 2 1 2 Data Validit
36. k for a 10 100Mbps Ethernet connector a Micro HDMI port a MIPI Camera Serial Interface connector an UART console port a slot for SD cards an Audio Out an Audio In a 50 Pins Interface for LCS GPIO ADC I C and SPI and a e MMC module socket 3 4 2 Specific Task The Odroid X2 is the brain of the Racer and uses an embedded Multimedia Card e MMC with 16GB The operating system running on the Odroid is a specialized Xubuntu 13 04 distribution where the program for controlling the Racer is executed 3 4 3 Presetting As described above the Odroid X2 needs 5V supply voltage but is connected to a 12V circuit Therefore a voltage converter transforms the given 12V to the needed 5V The Xubuntu 13 04 distribution had to be installed on the eMMC to use the Odroid and tools to support the development for example qtCreator emacs and gnuplot 29 3 Components To accomplish that the program was able to communicate via the USB port with the external devices the access permission must be set 3 5 TopFuel LiPo ECO X 5000 35 3 5 1 Overview The TopFuel LiPo ECO X 5000 3S Hac shown in Figure 3 5 is a lithium polymer accumulator and is the power source of the racer It has three cells a capacity of 5000mAh and a nominal voltage of 11 1v It has a load duration of 20C and a weight of 377g Figure 3 5 Lithium Polymer Accumulator 3 5 2 Specific Task The accumulator provides the supply voltage and current for the MD25 EMG30
37. mission of bytes to the USB ISS the communication between the USB ISS and the MD25 via the I C bus and the control of the motors worked Hence the next goal was to read data of the accelerometer and the gyroscope The first step to reach the next milestone was to attach the MPU 9150 to the I C bus To achieve this the wires of the 12C bus were soldered on to specific pins of the IMU and the address was used as specified in the product specification Inv Running a first test however revealed another problem the IMU could not be detected Since the IMU has no LED to indicate whether a signal has been received correctly or not the wires were checked with a multimeter to confirm they were soldered correctly which was in fact the case The red LED of the USB ISS flashed whenever the application has send a command thus the interface must have received valid commands and the problem must be either occurred during the transmission via the 12C bus or on the IMU itself To exclude an error during the transmission the signal transmission was monitored with an oscilloscope It showed that the USB ISS transmitted the correct address but the IMU did not recognize it as its own and therefore it did not return an acknowledge signal This fact implies that the problem was either that the IMU was damaged or that the address was not the address the IMU expected Eventually the problem was that the specified address in the product specification disregarded the rea
38. n acknowledge signal and the master starts the transmission After each transmitted byte the receiver must send an acknowledge signal If the slave receiver sends a NACK signal the master will generate a stop or a repeated start signal If the receiver is the master and transmits a NACK signal the slave transmitter must release the SDA wire to allow the master to send a stop or a repeated start signal After all data was transferred the master generates a stop signal to notify that the transmission is over and to free the bus The Figure 2 7 and 2 8 show two different examples of data transmission ST Slave Address R W ACK Data ACK Data ACK NACK Sp Figure 2 7 Sequence of requesting or transmitting data ST Slave Address W ACK Data ACK Data ACK NACK RST Slave Address R ACK Data ACK Data ACK NACK Sp Figure 2 8 Sequence of combined transmission with the help of the repeated start signal 15 2 Background 2 1 6 Arbitration As described above the I C bus allows to connect multiple masters To avoid conflicts and guarantee that only one master is active at one time the I C protocol provides the arbitration solution A master is able to start a transaction only if no other transmission proceeds and therefore no other master blocks the bus Sometimes it is possible that several masters start a transaction at the same time which leads to conflicts To avoid this the arbitration ensur
39. n was used That means whenever a connection to the USB ISS is needed the program checks whether a connection is already established If so the program will not open a new connection but returns a reference to the existing connection object This ensures that all objects use the same connection to the USB ISS and do not impede each other Although this reduced the occurrence of the error but it did not solve it entirely This is where the termios library came in It provides the ability to configure how to transmit data between devices and offers methods to manipulate the transmission For example it allows to change the transmission mode to a raw mode In this raw mode characters are processed one by one and special characters are not interpreted As a result of that the error that the device is temporary not available was eliminated but at this point a new error occurred The received data was not correct whenever the devices were read alternately After some further observations it became clear that the received values where in fact delayed The application received data that was expecting earlier and therefore the received data was assigned to wrong variables To fix this problem sleep functions were implemented because the process time of the external devices was disregarded but this did not solve the problem Tests showed that this problem occurred whenever the application requests data from the one device in one step and in the next step fr
40. ned with the 7 bit addresses This is possible because of structure of the transmitted bytes The first byte contained the bit sequence 11110 followed 14 2 1 PC by the 2 and 2 bit of the address and the read write bit For this reason all bit sequences starting with 11110 are reserved because this bit sequence indicates a 10 bit address The second byte contains the rest of the address l l J J12 o1x ix jaw IX IX IX XXX x x Figure 2 6 The structure of the two bytes containing the 10 bit address To transmit an address the master sends first a start signal and then the first byte of the address The master waits for an acknowledge signal from a slave with a 10 bit address If the master receives an acknowledge signal it will transmit the second byte which contain the rest of the address A device sends an acknowledge signal if it recognize the address as it own Now the data transfer begins 2 1 5 Data Transfer To transfer data the bus must not be marked as busy which means no transmission is in progress If this is the case the SDL and SCL wires are at HIGH level and consequently the 12C bus is ready for a new transmission To start a data transfer the master transmits the start signal followed by the address of a device After the start signal was transmitted the other devices switch into a listening mode and compare the transferred address with their own addresses The device with the transferred address returns a
41. next problem which occurred was that the MD25 was not able to set the desired speed of the motor in one controller cycle The MD25 changes the speed of the motors of maximum value 10 every 25ms but the controller cycle took only round about 15ms therefore the controller cycle must be prolonged In order to prolong the controller cycle sleep functions were implemented and afterwards the parameters of the PID controller had to be adjusted Another issue of adjusting the parameters was the fact that the reaction of the motors depend on the charge level of the accumulator After a while of trying to configure the controller it slowly became apparent that the motors have reached their limits with weight and inertia of the racer This results from the fact that the accumulator was attached on the top of the ladder and thus the centre of gravity was too high That means minor deviations from the balancing point made the racer falling over because the motors do not have enough power to compensated the velocity of fall Therefore the accumulator was mounted at the bottom of the ladder but now the racer became very unstable and started to oscillate Multiple positions for the accumulator were tried but every time either the centre of gravity was too high and therefore the motors were not able to react fast enough or had the power to compensate the velocity of fall to prevent the racer from falling over Or the racer was to unstable and started to oscillat
42. ng The gyroscope measures the angle change rate for each coordinate and the integral over time of these data represents how much degree the angle had changed in this period Therefore the gyroscope data of the y coordinate must be integrated over a certain time period and add it to the previously determined angle to get the current inclination angle of the racer 5 9 Remove the Angle Drift Now two methods to determine the inclination angle were known one to determine the inclination angle at start time with the help of the accelerometer and one to determine inclination angle while the Racer was moving with the help of the gyroscope Accordingly the 44 5 9 Remove the Angle Drift next task was to find a controller that regulates the motors based on the current inclination angle of the robot to prevent the robot from falling over To gather information about controllers and how other solutions solved this problem several different papers and other solutions have been studied A controller that was easy to understand and often used in different projects was the PID controller The PID controller is easy to implement and provides good results if the controller is applied correctly Consequently the PID controller was the right controller for this project After the PID controller was implemented the configuration of the parameters began But after a while of trying to set the parameters correctly the Racer was not able to balance longer t
43. nnection to the USB ISS on Linux operating systems Based on the source code of the application a short test program was written This program was able to set the operation mode of USB ISS was able to read the serial number the module ID and the firmware version of the device Once the program worked properly the next task was to figure out how to transfer data to an external device connected to the I C bus via the USB ISS In preparation of this the decision was made to upgrade the firmware of the USB ISS from version 4 to version 5 because it provides an additional very useful function It allows to check the bus whether a device with a specific address is connected This upgrade however was required to be performed on a windows machine since the official documentation does not provide a solution to upgrade from a Linux system After the update was done a device was required that could be connected the 12C bus to test the new function T hus the MD25 was attached to the bus To test the new function it was sufficient to supply only the microcontroller on the MD25 by the 5V supply voltage provided by the USB ISS After the function was tested and the MD25 was detected by the USB ISS the next step was to interact with the register of a connected device Due to the fact that the USB ISS is able to mange the start restart stop and ACK cycles automatically the data and commands must be stored in a byte array and transferred to the USB ISS The
44. not on the control deviation itself They react faster than p controllers even on small deviation But they are not able to detected permanent offsets Therefore a d element acts only in combination with a p and or an i element as a controller D elements calculates the rate of change of the control deviation and multiplies it with an amplification factor K The amplification factor determines how strong the controller reacts 22 2 6 PID Controller to the rate of change The equation of a d element is de t 2 4 y t Ka E 2 6 PID Controller The PID controller Rob13 con12 is a combination of a p i and d element Correctly applied the controller unifies the advantages and compensates the disadvantages of the three control elements The controller reacts fast on control deviation because of the p and d element The i element of the PID controller ensures that the offset disappears The controller reaches fast the set point has a small overswing and only for a short period Therefore the PID controller is fast stable and has no permanent offset The equation of the PID controller is the addition of the equations of the p i and d elements de t dt 2 5 g t K e t K e t dt Ka 0 2 7 Complementary Filter The complementary filter is used to combine multiple data In this project the filter is used to combine the inclination angles calculated by the accelerometer signal and gyroscope sign
45. nsures that during the burst read the values stored in the registers do not change therefore sampled values of the current cycle could not be mixed up with values sampled from the previous cycle After a period of coding the new software was at the same level as the test application but the new application ran much more stable and provided new functions for example the application was now able to store the data in a logfile for better monitoring and the ability to plot the results After some tests the results were plotted and it could be verified that the values of the accelerometer and the gyroscope were correct except for some small measurement noise The Figure 5 3 shows the raw data obtained from the IMU Now the application was able to read out the data of the IMU correctly and thus the third milestone was reached 41 5 Project 5 6 Connected all Devices to the same PC Bus The next step was to attach the MD25 IMU and USB ISS to the same bus but every time the application tried to request data from the MD25 or the IMU an error occurred The devices repeatedly were shown as temporally not available The issue was that the same serial port in one application was opened several times and the alternating transmission via different connections caused some trouble Therefore the program code was changed to allow at most one connection to the serial port instead of one for the MD25 and one for the IMU To accomplished this the singleton patter
46. o HIGH level and the data will be sampled at the first edge The first edge is a falling edge therefore the following data will also be sampled at a falling 18 2 2 SPI MISO Figure 2 12 SPI mode 1 edge see Figure 2 13 MISO Figure 2 13 SPI mode 2 CPOL HIGH and CPHA HIGH The idle state of the clock set to HIGH level and the data will be sampled at the second edge The second edge is a rising edge therefore the following data will also be sampled at a rising edge see Figure 2 14 MISO Figure 2 14 SPI mode 3 19 2 Background 2 2 5 SPI configurations SPI provides multiple configurations how the slaves can be connected to the master Mostly three configurations are used 3 Wire Master Slave the 4 Wire Single Master Multi Slave and the Daisy Chain 3 Wire Master Slave In the 3 Wire Master Slave configuration as shown in Figure 2 15 only three wires are required because only one slave is connected to the bus In this case the SS pin can be set fix to HIGH level and therefore the SS wire is not needed But some devices requires a falling edge of the SS line to start interaction and in this cases the SS line is still needed Master Figure 2 15 3 Wired Master Slave 4 Wire Single Master Multi Slave The 4 Wire Single Master Multi Slave configuration is shown in Figure 2 16 and is the mostly used configuration of a SPI bus Each slave has an independent SS wire connecte
47. oid A second voltage transformer was needed because the IMU receives the supply power not directly from the power source but from the MD25 The MD25 has an integrated 5V regulator to supply external circuitry and therefore supplies the 12C bus with supply voltage The IMU is supplied via the 12C bus but requires only 3 3V As a result of that a voltage transformer was integrated between the MD25 and the IMU This time a linear converter was used and worked properly because the amperage was not that high After all components were supplied with supply voltage and the IMU the MD25 and the USB ISS connected to the bus and mounted on the racer the application was copied on the Odroid Afterwards a test phase followed to check whether all wires are connected correctly and the application runs correctly on the Odroid which turned out to be the case 5 8 Calculate the Inclination Angle Now the assembly of the Racer was complete and the controller ready to be programmed hence the second phase of the project began The first goal was to determine the inclination angle of the racer To achieve this the accelerometer data and gyroscope data had to be processed in a way that the current inclination angle could be calculated The inclination angle was needed because depending on this angle the speed and direction of the motors should be regulated The first step was to consider how to determine the inclination angle at the start time The coordinate syst
48. om the other device In this case the next few requests return wrong values because the stream still contained old bytes A method that clear the input stream before the next request was needed The method tcflush from the termois library provided this capability and solve the problem Now the application was able to read out the data of the motors and IMU alternately and returned correct values The fourth milestone was reached 5 7 Put together the Two Wheeled Racer After the data transmission worked correctly the next task was to complete the assembly of the Racer Thais means to attach all components on the racer to connect the MD25 IMU and the USB ISS to the I C bus supply all components with the supply power and run the application to control the racer and devices on the Odroid Once all components were attached to the racer and connected to the bus the components needed to be powered by the supply power As supply power a lithium polymer accumulator that provides 12V supply voltage was used but the Odroid requires 5V supply voltage Thus 42 5 8 Calculate the Inclination Angle a voltage transformer was required At first a linear converter was used but it quickly became very hot and eventually shut down This happened because the Odroid requires up to 2A and the linear voltage transformer was not designed to handle such high amperage Therefore a step down converter was used and integrated between the power source and the Odr
49. on a inverted pendulum balancing on two wheels and was build with LEGO Mindstorms The core piece of the robot is the NXT a programmable robotics kit with a 32 bit ARM7 microprocessor To run the real time operation systems nxtOSEK on the ARM7 the bootloader was modified To prevent the robot from falling over a Linear Quadratic Regulator LQR is used and is a state based controller Three sensors are used to determine the system s state of the robot an accelerometer and a gyroscope to calculate the inclination angle and an encoder to determine the position and speed The main focus of the project was to stabilize an unstable system and rejecting disturbance 6 1 2 Hardware The structure of the robot was kept simple The centre of the robot is formed by the NXT unit On both sides of the NXT the two motors with the corresponding wheels are attached The gyroscope and accelerometer are mounted on the NXT 6 1 3 Software The software can be separated in three parts the initialization module the digital control system and the human machine interface The initialization Module has two task the first is to calibrate the gyroscope that means to determine the gyroscope offset The second is to initialize the required variables The digital control system consists of three modules the sampling module the estimation module and the LQR controller module The sampling module reads out the sensor data of the gyroscope accelerometer and encoder with
50. or Ground Hall Sensor B Hall Sensor A Hall Sensor Vcc Hall Sensor Ground Hall Sensor B Serial l2C Select Hall Sensor A Figure 3 2 MD25 26 3 3 MPU 9150 3 2 2 Specific Task The MD25 is connected to the Odroid X2 via the 12C bus and supplies the bus with 5V supply voltage The module acts as a slave device and controls the two connected EMG30 motors 3 2 3 Presetting Two configurations need to be done before the MD25 is used The first is a hardware configuration and must only to be set once It is needed to switch the MD25 to the I C mode This is achieved by removing the jumper of the configuration pins The second configuration is a software configuration that sets the acceleration of the motors and must be done each time the robot starts In order to set the acceleration the Odroid sends a write command via the USB ISS and the 12C bus to the MD25 after the program was started and a connection was established This command contains the index of the acceleration register and the value that should be written into this register After the acceleration is set the MD25 is ready to work 3 2 4 Procedure In each cycle the Odroid sends a write command via the USB ISS and the PC bus to the MD25 This command contains the register index of the motor and the speed value After the speed value is written into the register the MD25 increases or decreases the speed every 25ms based on the acceleration rate 3 3 MPU 9150 3
51. ore complex compared to this solution this results from the fact that the Racer is build out of several different components that are connected and communication via an IgC bus For this reason the Racer can be a easily and nearly arbitrary upgraded 6 2 Zilog ZNEO based Self Balancing Robot This approach was developed by Spemcer Bridette Bur07 6 2 1 Overview The Self Balancing Robot is a two wheeled robot It uses two reflective objective sensors to calculate the inclination angle The core piece of the robot is the Zilog ZNEO microprocessor The microprocessor process the data from the sensors and calculates the inclination angle which is used by an PID algorithm To prevent the robot from falling over the microprocessor generates signal based on the information provided by the PID controller to regulate the two servo motors Data is transmitted via the serial I O pins The robot forms an inherently unstable platform that is highly susceptible to tip over 6 2 2 Hardware The robot was constructed with the scooterbot kit The scooterbot kit contains two round plates with 7 in diameter two 3 wheels and two servo motors and the required screws and wires The two plates are attached with four risers to each other The bottom plate has cutouts for the wheels and brackets to mount the two servo motors The upper plate has a central hole to pass wires Additionally the two plates provide the possibility to mount extra devices The bracket
52. p 45 50 2012 Cited on pages 23 45 and 49 P Semiconductors The I2C bus specification Page 8 14 Cited on page 11 Sparkfun https www sparkfun com products 11486 MPU 9150 Last ac cessed 03 12 2013 Cited on page 27 Die Zweidrahtbussysteme 12C Bus und SPI Bus Eigenschaften Protokolle An wendungen im Vergleich der beiden Systeme 2008 Cited on page 11 All links were last followed on December 03 2013 58 Decleration I hereby declare that the work presented in this thesis is entirely my own and that I did not use any other sources and references than the listed ones I have marked all direct or indirect statements from other sources contained therein as quotations Neither this work nor significant parts of it were part of another examination procedure I have not published this work in whole or in part before The electronic copy is consistent with all submitted copies place date signature
53. program the logfiles will be closed and the speed of the motors set to null 35 5 Project 5 1 Initial Situation At the beginning of the project only the hardware components were available the MD25 with motors and wheels the MPU 9150 the USB ISS and the Odroid Based on these components the planing phase began 5 2 Planing Phase In the beginning phase of the project the first task was to specify the general conditions for the construction what kind of material should be used to construct the Racer how should the racer be designed and where should the components be mounted to reach a compromise between stability and high dynamics The choice of the construction material fell on wood because wood is a cheap raw material and it is easy to work with The look of the Racer is a bit like a ladder on two wheels T his design provides two advantages on the one hand there is enough space at the bottom of the Racer to mount most of the components On the other hand a weight can be attached at an arbitrary point of the ladder This makes it possible to change the centre of gravity and therefore alter inertia and dynamics of the robot Figure 5 1 shows a sketch of the Racer Figure 5 1 Sketch of the Racer 37 5 Project After the general conditions of the construction are clarified the technical details of the Racer had to be defined what kind of operating system programming language and communication system or protocol shoul
54. s of the motors were mounted from the bottom side to the bottom plate This modification were done because otherwise the robot was not able to tip over because the distance to the ground was to small On this brackets the sensors were mounted too The motor controller that regulates the motors is attached on the bottom plate and on the top of the upper plate the microprocessor is mounted The two motors are connected to a motor controller that receives signals from the micropro cessor The motor controller process these signals an regulates the motors based on these signals Attached to the motor are the two wheels The sensors are directly connected to the microprocessor ol 6 Comparison to other solutions 6 2 3 Software The architecture of the software is a layered based structure and consists of four layers the hardware abstraction layer the device interaction layer the integration layer and the user interface layer Each layer has a specific task but the interaction among the layers is not strictly hierarchical Hardware Abstraction Layer The hardware abstraction layer forms the interface to the microprocessor ports and registers and is required to interact with the onboard device peripherals for example to control the LEDs Device Control Layer The device interaction layer forms the interface to the external devices the motor controller and the sensors It provides on the one hand functions to retrieve data from the device
55. s or transmit commands to control the devices and on the other hand it provides the possibility to configure the devices The layer is also for the calibration of the sensors responsible Integration Layer The integration layer contains the PID controller In this layer the sensor data are processed and based on this information signals are transferred to the motor controller to control the motor and prevent the robot of tipping over User Interface Layer The user interface layer provides the possibility to interact with the robot during the runtime The main task of the layer is to test monitor and exercise the functions provided by the other layers 6 2 4 Controller To control the robot and thus prevent the robot from tipping over a PID controller is used The controller regulates the motors depending on the inclination of the robot To determine the inclination the two reflective object sensors provides the controller with data The sensor consists of an infrared emitting diode and a NPN silicon phototransistor These two components are mounted in a protective housing to minimize noises The phototransistor measures the reflected light from the LED and varies the voltage based on the measured value The voltage is converted into a digital signal to process the data Based on this data the values 52 6 2 Zilog ZNEO based Self Balancing Robot are mapped on a range from 1000 to 1000 The value 0 means the robot is vertical upright
56. t Bibliography 49 49 l 55 55 55 57 List of Figures 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 2 10 2 11 2 12 2 13 2 14 2 15 2 16 2 17 3 1 3 2 3 3 3 4 3 9 3 6 3 7 4 1 5 1 5 2 5 3 5 4 9 9 5 6 8 7 5 8 Data transfer the first bit is a logical 1 and the second bit a logical 0 12 Start signal iia eee ce en ge ee a a A Be 13 Stop signal as 2 8 Ka a e RES eee 13 Transmission of the byte 10110001 and acknowledgement with ACK 14 T bit address R W bit gi bw ee ar ee a see Kia 14 The structure of the two bytes containing the 10 bit address 15 Sequence of requesting or transmitting data 2 2 EI mn nn 15 Sequence of combined transmission with the help of the repeated start signal 15 Multi master conflict avoiding 2 2 CE nn nn 16 Data transfer among two shift registers 2 2 on on 18 REMOS OS a a eee a RE De a A is ae ge 18 SPI mode L si ce a a a ar De SE Bs 19 SPI mode 2 242 str aa ek he ee ee aa 19 SPL MOdES tt o ir iio Aula Sep gs dar Dee phe BE ne 19 3 Wired Master Slave onen 20 4 Wire Single Master Multi Slave 2 2 CE on on nn 21 Daisy Ch in sa ae ra Mean en pte Bele de 21 USB ISS ta a ae 25 MD25 2 4 5 0 o a ne on Aa u ee Seg 26 MPSS a a BN Sed a ok 28 Odrord 2 ee O a Ge Be N 29 Lithium Polymer Accumulator 2 2 22 on En 30 EMG30 u rar pete Ba Bei ee A A il 3l Two Wheeled Racer rn 31 Layered architecture
57. t more accurate As a result of that the software and controller can be extended so that the racer does not only try to balance but drive around After the Racer is able to drive around it can be used for different tasks for example a camera can be mounted on the Racer to sense the surrounding 55 Bibliography Bur07 Col07 con12 Deva Devb Deve ECM 08 Hac Har Inv Inv12 JR 75 S Burdette A Zillog ZNEO based Self Balancing Robot with PID control 2007 The George Washington University Cited on page 51 S Colton The Balance Filter A Simple Solution for Integrating Accelerometer and Gyroscope Measurements for a Balancing Platform 2007 Cited on page 23 Regler und Regelstrecken 2012 Cited on pages 21 22 and 23 Devantech http www robot electronics co uk htm md25tech htm Devan tech MD25 12V 3A Dual H Bridge Motor Driver Last accessed 03 12 2013 Cited on page 26 Devantech http www robot electronics co uk htm usb_iss_tech htm Devantech USB ISS Last accessed 03 12 2013 Cited on pages 25 and 39 Devantech http www robot electronics co uk htm emg30 htm EMG30 mounting bracket and wheel specification Last accessed 03 12 2013 Cited on page 30 M Euston P Coote R Mahony J Kim T Hamel A Complementary Filter for Attitude Estimation of a Fixed Wing UAV In IEEE RSJ International Conference on Intelligent Robots and Systems pp 340 345 2008 Cite
58. when the balancing point was reached This fact caused the problem that every time the Racer was driven in a direction to hold up itself and reached the balancing point only for a control cycle but did not change the inclination direction the motors stopped and the robot was falling in the same direction again Thus the controller tried to compensated the falling velocity again which caused a more and more unstable system To reduce this behaviour the offset was weighted depending on the angle between the balancing point and the current angle This was achieved by shifting the balancing point in the opposite 47 5 Project direction of the inclination direction the further the larger the inclination angle was The result was that the Racer now was able to hold up itself longer then before 5 11 Result The result of the project was on the one hand the Two Wheeled Racer which was build of several individual hardware components that communicate via an 12C bus On the other hand software that provide methods for requesting and transmitting data among the components and processing data The software also contains a PID controller that prevent the robot from falling over even if only for a time 48 6 Comparison to other solutions 6 1 Self Balancing Two Wheeled Robot This approach was developed by Brian Bonafila Nicklas Gustasson Per Nyman and Sebastian Nilson SAS12 6 1 1 Overview The self balancing two wheeled robot is based
59. y To send valid data bits the applied voltage of the SDA wire must not be changed while the applied voltage of the SCL wire is at the HIGH level Otherwise the signal will be interpreted as a control signal Figure 2 1 shows an example of a data transfer Figure 2 1 Data transfer the first bit is a logical 1 and the second bit a logical 0 The transmitted bytes are transferred with high bit first that means the Most Significant Bit MSB is the first bit transferred 2 1 3 Control Signals To control and initiate the communication among devices and to guarantee that only one sending and one receiving device is active at one time control signals are required Control signals can be identified by the change of the voltage level of the SDA wire while the applied voltage of the SCL wire is at HIGH level An exception to this is the acknowledge signal Start Signal To initiate a data transfer among two devices the master has to inform the other devices In order to inform the other devices the master sends a start signal which marks the bus as busy That means only the master which was sending the start signal is allowed to interact with another device and it is the only one which can free the bus again To send a start signal the applied voltage of the SDA wire must changes from HIGH level to LOW level while the SCL wire is at HIGH level Figure 2 2 depicts this 12 2 1 PC SDA SCL Figure 2 2 Start signal Stop

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