Difference between revisions of "S17: Sphero Droid"

Sensor's mounting platform

Motors

• DC Motors

The DC motors used in the project are 100 RPM low-cost single shaft straight geared motors. They are suitable for lightweight robots that do not require high power or torque.
The DC motors are connected to the wheels which are in contact with the base of the ball. The DC motors are driven by a driver module which controls the motor direction and speed.

Driver module

Control inputs of driver module

• Servo Motors

Write about the servo motor used and its uses.

Bluetooth Module

Bluetooth module HC-05 is used to communicate between the spherical robot and mobile application. It is implemented to establish the connection between the two so that we can remotely control the robot (to send start and stop signals) and receive the data from the robot directly on the Android application. The data being sent by the robot is current GPS location, ultrasonic range sensor values, and temperature sensor values.

Hardware Interface

We have four major hardware modules interfaced with a single SJOne board using different communication protocols. For simplicity sake, we have given a description of how each module is individually interfaced with the SJOne board. In reality, all these modules are connected to a single SJOne microcontroller.

Ultrasonic Range Finders

The ultrasonic range finders have been interfaced with the SJOne board using PWM. How is it triggered??

Ultrasonic range finders interfacing with SJOne board via PWM

Motors

The DC motor is connected with the SJOne board via the motor driver module using GPIO. The GPIO signals from SJOne board provide inputs to the motor driver module, which in turn drives the DC motors in forward or reverse direction or stop signal. Servo motor is interfaced with the SJOne board using PWM.

DC Motors and driver module connected to SJOne board using GPIO

Servo motors interface with SJOne board via PWM

The hardware interface of how the DC motors are connected to the wheels which are driven from the SJOne board and how the servo motor is connected with the pendulum to steer the robot in right or left direction can be viewed in the figure below.

Internal Hardware connection (Motors)

GPS Module

GPS module communicates with SJOne board via UART communication.

GPS interface with SJOne board via UART communication

Bluetooth module

The Bluetooth HC-05 module is connected with the SJOne board via UART communication.

Bluetooth connection with SJOne via UART

Software Design

PCB Design

SD Card Writing

Android Application

Software Design

Sensors logic

DC and servo motor logic

Implementation

GPS Module

Hardware Design

Venus GPS Module

Antenna for the GPS Module

The GPS module used in our project is Venus GPS logger (Venus638FLPx) by Spark fun Electronics. This module is the successor of Venus634LPx and it has a higher update rate and can be configured to operate at an update rate of 20Hz.It can be connected to the PC using a serial to USB converter and configured with the help of a GPS viewer software by SkyTraq which has a GUI and is easy to use.This is handled by the software by sending appropriate commands to the GPS logger when any option is selected by the user.

GUI of the SkyTraq GPS Viewer

By opening the correct COM port after connecting the GPS module to the PC, serial communication between the GPS module and PC can be established. The GPS logger works at a default baud rate of 9600bps but it can be configured to work at a baud rate of up to 115200bps. The changes in the configuration of the GPS module can be made permanent by writing the commands to the flash instead of the SRAM. The "Cold Start", "Warm Start" and "Hot Start" buttons on the bottom left corner of the screen define how fast a fix can be achieved by the GPS logger.

Hot Start: When a 3V battery is connected to the GPS module, it helps the GPS logger in saving information about the previous fix in its memory. This ensures that a fix is attained quickly when the system is switched on the next time. A warm start will happen if the module is switched on again before a specified amount of time, typically two hours.

Warm Start: As mentioned above if the module is switched on after about more than two hours then it will take a while for the module to attain a fix. It will take more time to attain a fix compared to the warm start, but is less than the time taken to attain a fix when the module is not fixed with a battery at all.

Cold Start: When a battery is not connected to the module at all then there is no information available about the previous fix and it would take a long time to attain a fix.

The output of the GPS module can be in NMEA format or SkyTraq Binary Message format. For sending the data from the GPS module to a controller it has to be configured to send data in the NMEA format. There are many message types in the NMEA format but for our project, the GGA type of NMEA output has been used which contains the time, position and fix related data for the GPS receiver.

The GGA message will have the following format

$GPGGA,hhmmss.sss,ddmm.mmmm,a,dddmm.m m m m,a,x,xx,x.x,x.x,M,,,,xxxx*hh<CR><LF>

                1      2       3  4     5 6 7 8 9    10   11
  

             1   UTC of position in hhmmss.sss format
             2   Latitude in ddmm.mmmm
             3   Latitude hemisphere indicator, ‘N’ = North, ‘S’ = South
             4   Longitude in dddmm.mmmm
             5   Longitude hemisphere indicator, 'E' = East, 'W' = West
             6   GPS quality indicator 
                    0: position fix unavailable 
                    1: valid position fix, SPS mode 
                    2: valid position fix, differential GPS mode 
                    3: GPS PPS Mode, fix valid 
                    4: Real Time Kinematic. System used in RTK mode with     fixed integers 
                    5: Float RTK. Satellite system used in RTK mode. Floating integers 
                    6: Estimated (dead reckoning) Mode 
                    7: Manual Input Mode 
                    8: Simulator Mode
             7   Number of satellites in use
             8   Horizontal dilution of precision
             9   mean sea level
             10  Differential reference station ID
             11  Checksum

Hardware Interface

GPS module is interfaced with the microcontroller via UART.

GPS Interfacing with SJOne board via UART

Software Design

Software Flow for the GPS

Implementation

SDCard

Hardware Design

Hardware Interface

Software Design

Implementation

Bluetooth module and Android Application

Hardware Design

Hardware Interface

Software Design

Implementation

PCB Designing

Hardware Design

PCB board

PCB Schematic

PCB board

PCB board } Hardware Interface Software Design Implementation Testing & Technical Challenges Describe the challenges of your project. What advise would you give yourself or someone else if your project can be started from scratch again? Make a smooth transition to testing section and described what it took to test your project. Include sub-sections that list out a problem and solution, such as: My Issue #1 Discuss the issue and resolution. Conclusion Conclude your project here. You can recap your testing and problems. You should address the "so what" part here to indicate what you ultimately learnt from this project. How has this project increased your knowledge? Project Video Upload a video of your project and post the link here. Project Source Code Sourceforge Source Code Link References Acknowledgement Any acknowledgement that you may wish to provide can be included here. References Used List any references used in project. Appendix You can list the references you used.