Spring 2016 Pathfinder Charging Control Circuit

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20160308_161724

by: Tuong Vu (Sensors, Actuators and Power)

Table of Contents

Introduction:

This document is to explain the charging control circuit of the pathfinder. The customer wants the pathfinder to have a self-charge capability. This circuit will help regulate voltage and circuit during the charging time of the batteries by the solar panel. The purpose is to prevent the damage to the batteries from overcharging.

Electronic Components:

  • 2 X resistors 1k ¼ watts
  • solar panel : NPower Amorphous Solar Panel Battery Maintainer Kit – 2.5 Watts
  • 2 X batteries : 10000MAh lead Battery
  • N- channel IRF840

Understand Components:

circuit

Figure 1

  According to the diagram above, two pins are reserved for this circuit from the Arduino, specifically   one analog pin and the other digital pin.  Analog pin is used for the intake voltage data from the voltage divider.  We implement the voltage divider to prevent damaging the I/O pins on the arduino, see table 1.  Ideally  the mosfet acts like switch such when voltage into the gate is much higher than the threshold voltage, the mosfet turns on, which means the drain and source  pins  are in series together. Arduino can generate a 5 volts output, which is enough to turn the mosfet on. When the  drain and source are connected the solar panel  is directly in  series with  the battery, allowing the current to flow and effectively charging the battery.

circuit1

The batteries and the solar panel switch place

 

Arduino Code:

Code  generates a  sequence of  addition   of  input voltage  taken from the  voltage divider,  which  will  go through  an if statement  in order  to   turn  the  Mosfet  on.

/*————————————————————–

Program:       Volt_measure

Description:  Reads value on analog input A2 and calculates

The voltage assuming that a voltage divider

Network on the pin divides by 11.

 

Hardware:     Arduino Uno with voltage divider on A2.

Software:      Developed using Arduino 1.0.5 software

Should be compatible with Arduino 1.0 +

Date:             22 May 2013

Author:          W.A. Smith, http://startingelectronics.org

————————————————————–*

// number of analog samples to take per reading

#define NUM_SAMPLES 10

int sum = 0;                // sum of samples taken

unsigned char sample_count = 0; // current sample number

float voltage = 0.0;                  // calculated voltage

int r8 = 8;

void setup()

{

Serial.begin(9600);

pinMode(r8,OUTPUT); // output pin.

}

void loop()

{

// take a number of analog samples and add them up

while (sample_count < NUM_SAMPLES)

{

sum += analogRead(A0);

sample_count++;

delay(10);

}

// calculate the voltage

// use 5.0 for a 5.0V ADC reference voltage

// 5.015V is the calibrated reference voltage

voltage = ((float)sum / (float)NUM_SAMPLES * 5.015) / 1024.0;

// send voltage for display on Serial Monitor

// voltage multiplied by 11 when using voltage divider that

// divides by 11. 11.132 is the calibrated voltage divider

// value

Serial.print(voltage * 11.132);

Serial.println (” V”);

sample_count = 0;

sum = 0;

if  (voltage < 4)

{

digitalWrite(r8,HIGH);

//delay(5000);

}

else if ( voltage > 4)

{

digitalWrite (r8,LOW);

//delay(5000);

}

}

//delay(100000)    .

This code was written by W.A. Smith, but is modified with the if statement by us. The Arduino is taking samples and applying them through the equation in the code ( see code) thus gives the voltage increment  we need. The output voltage generated by the arduino is the 8  digital pin,  this is where  the mosfet going to get the voltage to turn on or off.

table

figure 2 ATmega 328P specifications

Test results

result1

The above picture shows that the battery has 5.04 V before charging

result2

This picture shows that the battery now has 7.77 V after charging

Source Materials:

Arduino: Read Analog Voltage click here

NASA: How do Photovoltaics Work? click here

Spring 2016 Pathfinder Design and Manufacturing – Tilt System Design

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tilt system

By: Lindsay Levanas (Design and Manufacturing)

Table of Contents

Introduction

In view of the fact that Spring 2016’s Pathfinder will utilize both a Google Tango tablet and a phone as the main viewing system,1 the tilt system will be primarily designed around these two objects. Note that the pan system already in place on the current Pathfinder design will remain, allowing for the tilt system to be added on to it to form a complete pan and tilt system.

Tablet Encasement

As stated in the level 1 requirements, the Google Tango tablet must be encased for it’s own protection.1 To allow the user access to the tablet, a box with lid design was chosen, with the lid having a cut-out window for the tablet’s primary sensors. Measurements for the tablet are as follows:

Height: 4.72 in

Width: 7.73 in

Depth: 1.5 in

Note that the height and width measurements came from the tablet’s specifications.2 The depth however had to be measured as the tablet’s back shape is uniquely slanted as seen below in Figure 1 and 2.

figure1

Figure 1
figure2

Figure 2

Therefore to allow for the tablet sensors to aim forward, the flat side of the sensors needs to be aligned with the phone and the resultant distance between the two measured. While slightly difficult to accurately document, Figure 3 and 4 attempts to pictorially illustrate this.

figure3

Figure 3figure4

Figure 4

Therefore, the inside depth of the tablet box is 1.5in.

Next the placement of the necessary sensors on the tablet must be measured so that the cut-out window in the lid can be properly placed. Using Figure 5, 6 and 7 as a guide, the sensors were found to be enclosed in a rectangle 1.6 inches from the tablet’s side edges and .8 inches from the top.

figure5

Figure 5figure6

Figure 6figure7

Figure 7

Lastly, to ensure that the tablet fits into the box, .02 inches was added to both sides of the height, width and depth totals while the thickness of the box was chosen to be .23. Therefore, the tablet box (with lid) measurements are as follows:

Inside                               Outside

Height: 4.76in                                5.22in

Width: 7.77in                                 8.23in

Depth: 1.54in                                  2in

 

Phone Encasement

Similar to the process used above, the box for the phone was designed around the measurements listed in the body specifications.3 Adding the same extra room as the tablet for the phone to fit and the same box thickness, the dimensions become as follows:

Inside                                Outside

Height: 5.69in                                6.15in

Width: 2.82in                                 3.28in

Depth: 0.31in                                  .77in

Again following the same procedure for the lid cut-out as was done for the tablet, the camera hole was found to be a .68in square centered 1.41 inches down from the center top of the lid. Figure 8 and 9 were used for reference.

figure8

Figure 8figure9

Figure 9

Attaching the tablet and phone

To line up the phone’s camera with the tablet’s sensors, the two encasement boxes share circular cut-outs for screws to hold them together. For the tablet box, this means 2 screw holes on the top and bottom edge centered 1.645 inches from the top center of the box. For the phone box, this means 2 screw holes on the sides centered .5 inches from the top and 2 screw holes on the sides centered 5.725 inches from the top. When all aligned, the phone’s camera and the tablet’s sensors will now be on the same level.

 

Swivel point

For the phone and tablet box (hereafter referred to as tilt box) to be able to tilt, the midpoint of the system needs to be found. Taking into account the height of the tablet box and the width of the tilt box, a cylindrical extrusion is added to one side of the tablet box 1.64 inches deep from the back. Mirroring this, the other side will contain two holes of equal distance apart from the same center point so that a servo can be attached.

 

Tilt base

To hold both the servo and tilt box, a base is needed to connect the two sides. The width of this base will vary depending on the servo used, but the height is based on the height of the pan servo already attached to the current Pathfinder, as the tilt system will be structured around it. Considering a sample servo of width 1.75 inches, the base of the tilt system should be at least 10.48in (the width of the servo + the width of the tablet box). The height should be at least 2.125 inches from base to phone box in order to clear the pan servo.

 

Finished Product

figure10

figure11

 

Source Material

  1. Spring 2016 Pathfinder Preliminary Design Documentation, Level 1 Requirement, 2/19/16 http://arxterra.com/spring-2016-pathfinder-preliminary-design-documentation/
  2. Project Tango Development Kit User Guide, Technical specifications, 8/6/2015 https://developers.google.com/project-tango/hardware/tablet#technical_specifications
  3. Samsung Galaxy S6 – Full phone specifications, Body, http://www.gsmarena.com/samsung_galaxy_s6-6849.php

Spring 2016 Pathfinder Preliminary Project Plan

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WBS

By:

Peiyuan Xu                        (Project Manager)

Xiong Lee                          (Mission, System and Test Engineer)

Table of Contents

Work Breakdown Structure

by:

Peiyuan Xu                         (Project Manager)

WBS

This work breakdown structure demonstrate all the work needed to be done for this project Pathfinder Rover. There are four branches that indicates different job duties and division works assigned to the system and subsystem engineers.

Project Schedule

Top Level Schedule

schedule1schedule2schedule3schedule4

The charts above shows the preliminary project schedule and tasks that assigned to team members. Each task has a start date and end date indicated the period of the task.

Burn Down and Project Percent CompletionBurn Down

project overview

 

The Burn Down graph shows the overall project progress and remaining time to complete the project.

The Project Overview graph shows the project percent completion directly from calculation.

System Resource Report

by:

Xiong Lee                                   (Mission, System and Test)

Mass Report

mass report

Our mass is capped to 10 pounds or 4535.92 grams. Looking through the report, we have a contingency of 2519.56 grams. Our total expected mass should be a little over half the mass capacity of the rover. Most of the materials we are using are ABS plastic which is 3D printing. These materials are very light and will help us achieve the goal of staying under 4535.92 grams.

Power Report

power report

The Power budget is how much current our electronics draw. This report is from the specification sheets only. We have not measured the current these electronics draw. Our goal is to use this report to choose a battery that can give us 4 hours of run time. We will have to limit what we put into our design. The motors are the hardware that draws the most current.

Project Cost Estimate

Cost report

Our budget that we have is 500 dollars. We are reusing some of the parts that were on the previous pathfinder. Most of the parts we are reusing are the electronic parts. We need to figure out how many battery we need to run for 4 hours. We added two batteries onto the cost budget. We have a contingency of $225.12 dollars. With a margin of 82 dollars, we have $143.12 left under the budget.

 Source Materials

http://www.amazon.com/Baitaihem-Arduino-Wireless-Bluetooth-Receiver/dp/B00J1D6UBA

 

https://www.pololu.com/product/2507/specs

https://www.adafruit.com/products/191

http://www.gearbest.com/development-boards/pp_43066.html

http://www.tenergy.com/31016

https://www.sparkfun.com/products/13784

 

 

 

Spring 2016 Pathfinder Preliminary Design Documentation

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opp rover

By:

Peiyuan Xu                        (Project Manager)

Xiong Lee                          (Mission, System and Test Engineer)

Juan Acosta                      (MCU Subsystem and Control Firmware)

Tuong Vu                          (Sensors, Actuators and Power)

Lindsay Levanas             (Design and Manufacturing)

Table of Contents

Program Objective/Mission

By:  Peiyuan Xu (Project Manager)

The spring 2016 Pathfinder Rover was inspired by the design of NASA’s MARs Exploration Rover-“Sojourner”. The purpose of this Rover is to explore the beauty of CSULB campus at night in a self-sufficient way. The Pathfinder is allowed to have the solar panel charging the battery for up to 8 hours during the day time. Then the customer will spend 4 hours at night walking and exploring with the Pathfinder . The customer can use Arxterra control panel on the PC to navigate the Rover by using the cursor to click a point on the map. This generation of Pathfinder Rover is designed to test and implement SLAM (Simultaneous Localization and Mapping) technology for autonomous vehicles.

Program Requirement

  1. The Pathfinder project must be completed by May 2, 2016, the last day of EE 400D class. (From the Syllabus here)
  2. The cost of the project should be limited to $800 (Need customer verification)
  3. The Project Final Documentation must be turned in by April 25th, 2016. (From the syllabus here)

Project Level 1 Requirement

  1. The pathfinder shall be able to explore the terrain at CSULB campus at night
  2. The speed of the pathfinder shall be slower than human walking speed and faster than the Sojourner rover.
  3. The pathfinder shall be able to explore the campus at an interval of 8 hours charging (during day time) and 4 hours run time (during night time).
  4.  Sealed electronic enclosure required to protect electronics from dust
  5.  The pathfinder shall be self-sufficient by using 3 solar panels
  6.  Sealed pan and tilt system for the Android phone/Google Tango Tablet.
  7.  The tango will be able to gather depth perception data and send it to the Arxterra control panel.
  8. The pathfinder shall be able to go to the place wherever the cursor points on the Arxterra control panel.
  9. The customer shall be able to see what the rover sees on the camera

Source Materials

  1. Fall 2014 Pathfinder Preliminary Design here
  2. Curiosity Rover Wiki here
  3. Getting start with Project Tango API here
  4. Google Project Tango Overview here
  5. Project Tango Indoor Mapping here
  6. Project Tango Intro to Point Cloud here
  7. Project Tango Intro to Depth Perception here
  8. Autonomous Quadrotor Flight Based on Google’s Project Tango here

Design Innovationcreativity3

creativity1 creativity2 creativity4
creativity6

 

System Requirements (Level 2 Requirements)

By:  Xiong Lee (Mission, System&Test)

  1. In order to navigate through the terrain of the CSULB campus, the suspension and chassis will be designed to clear at least twice the diameter of the wheel. (found in the mars rovers) The Rocker Bogie design will be implemented to achieve a clearance of at least two times the diameter of the wheel.
  2. Due to the customer’s request to not go faster than walking speed, the pathfinder will not exceed 3ft/sec (about 2 mph).
  3. The motors will be calculated to ensure it will not go faster than 3ft./sec.
  4.  Results: TBD
  5.  The motors will be able to climb up an incline of 45 degrees. An experiment will be conducted to see what motors we need to get to achieve this requirement.
  6. The pathfinder will go faster than the curiosity rover (3in/sec). The motors will be calculated to go faster than 100m/sol.
  7. To explore the campus for 4 hours at night, we will install the battery or batteries to handle this run time.
  8. The solar panel will be able to charge the pathfinder 8 hours so it can finish its mission of running for 4 hours.
  9. The electronic enclosure will be made out of ABS plastic material to protect the electronics.
  10. The pan and tilt system will be 3D printed and designed like the previous semester.
  11. The pan and tilt system will be slightly modify to accommodate the dimensions of the Google tango tablet.
  12. The Tango tablet will need to be able to communicate with an app to receive data from its point cloud to the control panel.
  13. To see whatever the rover sees, LED lights will be installed onto the pathfinder, so the customer can see whatever the rover is in front of.
  14. To make sure we don’t waste power to the LED lights when it’s still got enough light to see, there will be a switch and light sensor to turn the lights on and off.
  15.  The pathfinder will go from 0.5 to 4 meters when clicked on the control panel. (The tango can scan approximately from 0.5 meters to 4 meters).

Source Materials:

  1. Mars Exploration Mission (Overcoming Obstacles) here
  2. Bogie Runt Rover (with chassis and Rocker Bogie Suspension) here
  3. Study Compared Older and Younger Pedestrian Walking Speed here
  4. The Mars Science Laboratory Mission here
  5. Arxterra Mini-Rosco Pan and Til System here
  6. Google Project tango overview here

Product Breakdown Structure

pbs

 

The main parts from hardware to software of our pathfinder is shown in the above PBS (product breakdown structure). Starting from the hardware, the chassis needs to be chosen to be able to handle the terrain in CSULB campus. One of the better idea we got was to use a rocker bogie system similar to the mars rovers. (Curiosity, Spirit and Opportunity, and Sojourner). The mars rovers are able to handle the harsh terrain of mars so choosing this suspension system would be a good choice to start the design. A pan and tilt system need to be installed to the pathfinder so we can scan the area with our Google Tango and android phone to be able to gather data on how far everything is. The solar panel needs to be able to charge up our battery during the daytime so we can have the Pathfinder running for good amount of time at night. Lastly, the software needs to be able to control everything on the hardware side to make sure the pathfinder will run correctly.

Electronic System Design

By: Juan Acosta (MCU Subsystem and Control Firmware)

Tuong Vu (Sensors, Actuators and Power)

System Block Diagram

system block diagram pathfinder

In the system block diagram, it shows how everything is connected to be able to control the pathfinder. The pathfinder will be running on mainly the arduino. The arduino will have a bluetooth module to communicate with the android phone and the control panel. On the arduino, there is a motor shield that will be able to run the motors in forward or reverse. It will also control the servos of the pan and tilt system to scan 180 degrees. To run the arduino, a battery will be installed and charged with the solar panels. Our main component is the Google Tango which will be use to 3D scanning the environment and send the depth perception data to the PC which will then give command to Arduino to control the Rover.

Subsystem Requirements

  1. The solar panels will have to charge the batteries for the Pathfinder in order to allow a 1:2 run ratio. (ex. 30 mins. run, requires 60 mins. charging time.) Current candidates require more testing of motor current draw.
  2. The solar panel(s) will resemble the Arxterra shape logo. In order to achieve this, we will be using multiple solar panels. (minimum of 3, maximum of 6 for weight and size concerns.)
  3. The Arduino Mega will act as a Voltage controller for the motor shield for the PWM supplied to drive the motors.
  4. The Arduino Mega will act as a charge controller in order to prevent the batteries from over charging and generating unwanted heat.
  5. The software code will allow the Pathfinder to drive forward, turn left or right, and rotate 90, 180, or 270 degrees.
  6. The Arduino UNO will control the pan and tilt servo for field of view through the android phone.
  7. The android phone will be used to communicate with the Bluetooth component and the Arxterra Control Application.

Power Flow Diagram

Power Flow Diagram

Battery is going to be the source of the power for the pathfinder, and many type of battery can be used in this application. The battery has to be able to deliver enough voltage and current to both the Arduino and motors & servos. High voltage has the potential of damaging the motors & servos and Arduino. Thus, buck regulators are installed in order to lower the incoming voltage from the battery. Over charging the circuit will result in damaging the battery, so a charge/discharge circuit will govern when the battery will connect to the solar panel or not.

Code Block Diagram

code block diagram

The Code Flow Chart shows how the Pathfinder will operate. It will be able to operate manually or on autopilot. Manually controlling the Pathfinder will involve the Android phone being used as a medium between the Arxterra Control Center and the Pathfinder’s commands. On the other hand, the autopilot feature will involve the Point Cloud System. Based on the depth perception data from the Google Tango tablet, communication will occur between the Tango tablet and the Arduino and allowing the pathfinder to voyage to set destination.

Interface Definitions

interfacematrix

The interface matrix above details the connection between the microcontroller and the motor- shield, solar panels, and Bluetooth module. It also indicates that the Arduino UNO will use pins to control a servo, monitor voltage, and act as a charge controller by monitoring the solar panels.

Mechanical Design

By:  Lindsay Levanas (Design and Manufacturing)

Mechanical Design

The above model illustrates Pathfinder’s conceptual design based off of both the level 1 and level 2 requirements. As stated in the level one requirements, Pathfinder must be solar powered, hence the thin rectangles on the top of the body.  A pan and tilt system for either an Android phone and Tango tablet is required and is modeled as a box (the length and width of an Android phone2) on a pole. The box will contain the phone (and Google Tango) and the wires will run down the inside of the pole into the body of Pathfinder. Pathfinder’s body then will house the electronics in a sealed enclosure as defined in the level 1 requirements. Lastly, Pathfinder will utilize a rocker bogie suspension system as a level 2 requirement to meet the level 1 requirement of being able to explore the CSULB campus

Source Materials

Axterra Website here

Android Phone size  here

 

Design and Unique Task Description

Power System Design

By:  Tuong Vu (Sensors, Actuators and Power)

Here are the specifications of our motors, wheels, and chassis.

motors (6) 140 Pre-wired motors
wheels (6) 2.55” Press Fit Wheels
Chassis (1) ABS Robot Chassis

Our servos with be the same servo used by the previous team. Using lithium battery will reduce the charging time of our rover, the specification of the battery is as the following (Tenergy 31016 Lithium Li-Ion 18650 11.1V 4400mAh Battery Pack).  We are planning to use two of them, one for two front wheels and the other for the two wheels in the back.  Our solar panel is going to be Solar Panel – 9W; we need 3-4 panels to have enough voltage to charge the batteries. Using two DC-to-DC (4.5 – 45V to 3.0 – 35V) Converter Module Board Step Down Transformer Module – BLUE, we can step down the incoming voltage from the battery.

Power system design

 

Source Materials

  1. Battery we need is here
  2. Dimension of the solar panel here
  3. DC to DC converter module board here

More on Mechanical Design

By:  Lindsay Levanas (Design and Manufacturing)

  • Rocker bogie design

    • Structure must be such that Pathfinder’s chassis can clear twice the wheel’s diameter. To do this, the distance between the bottom of the chassis and the bottom of the wheel must equal twice the wheel’s diameter.
    • The struts must be calculated to allow for level orientation of the chassis. Back-of-the-envelope calculations used for the 3D model are provided below however more formal calculations will be needed for the final design.
  • Rocker Bogie back of envelope
    • Material and cable tree for the rocker bogie suspension system will need to be defined.

  • Solar panel layout and shape

solar panel designOnce the power systems engineer has selected the solar panels, they will be balanced on the top of Pathfinder in the shape of the Arxterra logo. The rough sketch the 3D model is based on is shown above, however more accurate measurements will need to be made once the solar panel dimensions are known.

  • Pan and tilt system

    • The materials, dimensions and location of the pan and tilt system will be based around the mapping device (either Android phone or LIDAR) selected for Pathfinder.
    • The servos will be housed inside the main body of Pathfinder.
    • Wires will be contained inside the pan and tilt structure.

     

 

 

Spring 2016 Pathfinder Research Project

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pf1 pf2

 

By:

Peiyuan Xu (Project Manager)

Xiong Lee (Mission, System and Test Engineer)

Juan Acosta (MCU Subsystem and Control Firmware)

Tuong Vu (Sensors, Actuators and Power)

Lindsay Levanas (Design and Manufacturing)

 

Table of Contents

Project Manager Research

 

Source Material

  1. Pathfinder Preliminary Documentation. 11/12/14 http://arxterra.com/wp-content/uploads/2014/11/Pathfinder-Preliminary-Documentation.pdf
  2. Pathfinder Final Documentation. 12/12/14 https://www.arxterra.com/pathfinder-final-documentation/
  3. Pathfinder Course Mapping. 10/30/14 https://www.arxterra.com/pathfinder-course-mapping/
  4. Pathfinder Final Video. 1/20/15 https://www.youtube.com/watch?v=p75FGE_HQl0

Review of Literature

Analysis of Past Level 1 Requirements 

Requirement Evaluation Rubric:

  1. Is the requirement, Quantitative, Verifiable, and Realizable?
  2. Is the requirement response to customer’s expectations?
  3. Does the requirement move the design process forward?
  4. Does requirement provide links to source material?

Rubric

 

Spring 2016 Discussion of Requirements from Fall 2014:

The Group clearly stated the issue that automation industry meets and the needs for them to develop autonomous and self-Sufficient machines. The project objective was generated properly based on the customer’s expectation. However, on the requirements level, the group did not use enough quantitative, verifiable, and realizable thinking to write their level 1 requirements. For number 5 and 6 of their requirements, there was no quantitative variables that can be measured or proved to meet their requirements. Those requirements could be improved by mentioning more details of the environment such as quantitative temperature, wind speed, dust level, etc. In addition, the word “shall” should be used instead of “must” in those two requirements. Some of the requirements are lack of source links for us to research them in details. Their preliminary research posted nearly at the end of the semester and included level 2 requirements as well. Their final documentation and preliminary research had very much the same content. Their final video documentation was made properly as it contains their design of work and testing activities. But one thing I noticed that for the video documentation, they did not include the final testing of Pathfinder running in the Mediterranean environment which was one of their requirements.

 

Spring 2016 New Project Objectives:

  • Pathfinder should be able to explore the desert area for a whole day.
  • Google Tango tablet will be used and installed onto the Pathfinder.
  • Solar panels will be used to charge the batteries.
  • Pathfinder allows to move certain amount of time and stops to wait for solar panels charging the battery and then continue exploring.
  • Pathfinder should autonomously go to a destination by clicking a point on the photo that google tango captures.
  • Make the Pathfinder cool

 

Spring 2016 New Level 1 Requirements:

Many changes will happens on the Pathfinder this semester. These include using solar panels to charge the batteries and also google Tango tablet will be used to navigate pathfinder instead of using GPS navigation/waypoints. Therefore our requirements will various from Fall 2014 semester. These may include:

  1. The pathfinder shall be able to handle the desert terrain. Meaning it will function properly for up to 100 degrees and has proper suspension system that can handle bumpy road condition.
  2. The pathfinder shall be self-sufficient by using solar panels.
  3. The pathfinder will explore the desert for at least 15 minutes and then it will recharge for up to 1 hour and repeat the steps for the rest of the day.
  4. Sealed environment for microprocessor, electronic components and Tango tablet
  5. An extra portable charger will be used to charge Tango tablet separately or an extra small panel will be used to do so.
  6. The weight of Pathfinder shall not exceed 17 pounds

 

Spring 2016 Preliminary Budget:

For our preliminary budget, we will assume to spend up to $150 on appropriate solar panels that have enough power to charge batteries in short amount of time. The Google Tango can be borrowed from the president form CSULB HKN society. Other mechanical parts and electronics can cost up to $150. Total cost will be limited to $300 negotiable.

Spring 2016 Discussion of Schedules:

  • The final project will be due on May 9th (The Final Exam date).

http://web.csulb.edu/depts/enrollment/registration/final_exam/spring_chart.html

  • It is important to break down project to small tasks and schedule the due dates for each task. The project breakdown structure will be done by system engineer and from that, due dates for each task will be determined and announced by project manager.

 

Systems Engineer Research

By Xiong Lee (Mission, System, Tests)

Source Material:

Level 2 Requirements from Fall 2014 semester:

sy1 sy2 sy3 sys4

Summary of Level 2 Requirements:

Overall, their level 2 requirements were very good. They gave good documentations of what they did for their level two requirements. For example, how they designed their pan and tilt system for their android phone. There were things that could have been better documented. They didn’t list sources where they got the specs of their batteries, shield, arduino from.

Microprocessor and Arduino:

  • Atmega 2560 microprocessor
  • Arduino mega ADK
  1. Specs of the arduino
Microcontroller ATmega2560
Operating Voltage 5V
Input Voltage (recommended) 7-12V
Input Voltage (limits) 6-20V
Digital I/O Pins 54 (of which 15 provide PWM output)
Analog Input Pins 16
DC Current per I/O Pin 40 mA
DC Current for 3.3V Pin 50 mA
Flash Memory 256 KB of which 8 KB used by bootloader
SRAM 8 KB
EEPROM 4 KB
Clock Speed 16 MHz
USB Host Chip MAX3421E
Length 101.52 mm
Width 53.3 mm
Weight 36 g

Found on the website:

https://www.arduino.cc/en/Main/ArduinoBoardMegaADK

Some proposed level two requirements based on our level one requirement:

  1. A better electronic enclosure will be designed to keep the electronics protected (cooled).
  2. The solar panel should be able to charge the two 7.4 volt batteries for the motor as well as the 11.1 volt system battery.
  3. There will be an enclosure for the tablet to protect it from the environment.
  4. There will be Bluetooth communication from the tablet and arduino.

Testing:

Their testing of their products can be found here. They tested their GPS, Communication Bluetooth, batteries, weight and height clearance and their coding. Most of these testing had good documentations of what they did in the experiment. One thing was where they got their sources material from. They didn’t show sources to how the battery should be tested or etc…

 

Flowcharts/System block diagram:

http://arxterra.com/pathfinder-axterra-gps-communication-part-three/

http://arxterra.com/pathfinder-code-flowcharts/

http://arxterra.com/pathfinder-arxterra-communication-commands/

http://arxterra.com/pathfinder-pin-interface/

Their flowcharts and block diagrams were good. They specified everything they had on the pathfinder from their three batteries to the Bluetooth and GPS. For our system diagram, we’ll have to add the tablet and solar panel into the diagram. Our flowcharts will change because we have a different mission than what they have from the customer.

 

Interface System:

Their use of a separate pcb to store the sensors, regulators, Bluetooth, etc… (Shown above in the system block diagram) helped them make their electronics and wiring cleaner. Their diagram showed how each product interfaced with each other. On our project, we’ll have to make our Google Tango tablet communicate with the Arduino on the pathfinder. We’ll also have to use the arduino to communicate with the solar panel so it can charge up the batteries of the system and motors.

 

Electronics and Control Research

Sensors, Actuators and Power

By: Tuong Vu

E&C Division

Level 2 Sub-Requirements: (Based upon original level 2 requirements)

Servos :

  • The servo must be able to support the weight of the Google Tango, which is about 82 lbs. (370 g). Google tango  needs  to  be  on the  a  rotating platform in order to  navigate  the  pathfinder;  therefore,  the  servo  needs to have the capability  of rotating 360 degree.

Motors :

  • Generate enough torque to rotate the wheels in order for the chassis to move.
  • Need to handle  high  current
  • Protect these motors with a Buck regulator.

Battery.

  • Battery needs to supply enough voltage and current to drive the motor.
  • Keep stock battery.
  • Ni-Lithium battery 10000ma at 5 volt for Google Tango.

Solar panel.

  • The solar panel has to fit the pathfinder, and the weight of solar panel should be around 5 lbs. max. Need to be able to deliver enough current and voltage to charge the Google Tango   and motors’ batteries.

Buck regulator.

  • Batteries and motors protection, a simple buck converter can be used to step down the voltage. This is critical, over charging the battery   and oversupply the motors lead to heat building up within the components.

Charge/ discharge voltage regulator

  • Charge/ discharge voltage regulator disconnect or connect batteries from the solar panel at a certain voltage range. Pathfinder will have self-charge capability with this circuit installed.

Device Recommendations & Test Proposals:

Servos:

  • We will be using the stock motor from the previous class. (This decision may change in the future)
  • Test Servo to see if it can hold 5 lbs.

Motors:

  • We will be using the stock motor from the pathfinder. Base on testing, our motor needs about 1.8 voltage and 1.6 amps to turn on.
  • Test for the motor voltage and current required to turn under various load.

Solar Panel.

ec1

  • Conduct solar panel test to find the average output voltage and current.
  • Test charge/discharge circuit by using it to charge a 12-voltage 10A battery with the solar panel.

Buck regulator:

  • The role of the buck is to lower the voltage from the solar panel to the motors, protecting them from shock or heat damage. The current motor  on the path finder  is about 1.8 voltage  to turn on, so buck  regulator  needs  to lover  the voltage from the  solar panel or battery  down to 1.8 voltage.  Texas Instrument, Digi-key, and Mouser Electronic have the Buck Regulator we need for our project. We can self-build the Buck Regulator circuit.
  • We need to conduct some test to make sure the Buck Regulator can integrate with circuit.

Charge /discharge voltage regulator.

  • We will have to design this circuit from the ground up. The idea is using a power P–Channel Depletion Mosfet as a switch to control the flow of current from the solar panel to the motors’ batteries and Google Tango Tablet.
  • We need to build and test the design to make sure circuit can connect and disconnect the batteries from the solar panel.

Battery

  • We are using batteries from the previously installed on the pathfinder.
  • Test for the Maximum Voltage level of the batteries, in order to calibrate the voltage level that the “Charge /discharge voltage regulator” has to disconnect the batteries from the solar panel.

 

MCU Subsystem and Control Firmware

By: Juan Acosta

Source Material:

  1. Arxterra Website, Arduino

https://www.arxterra.com/rosco-and-pathfinder-arduino-code-versions-available/

  1. Arxterra Website, GitHub, Pathfinder_Rover

https://github.com/arxterra/Pathfinder_Rover

  1. Arxterra Website, Pathfinder, Pathfinder Final Documentation

http://arxterra.com/news-and-events/members/pathfinder-4/

 

Discussion based on previous Level 1 & 2 Requirements:

The previous design of the Pathfinder used modified Servos for pan and tilt control of the phone. Instead of modifying an existing servo, they should have bought an inexpensive servo with no limitations on turning radius to solve this minor issue. This could have saved a little time and helped moved the project along by allowing more time to focus in other areas that were having major issues.

The main loop program flow for the previous Pathfinder project was successful in drawing out the tasks of the Pathfinder. They implemented simple true or false checks in order decide what action the Pathfinder should take next. This looks like a fast, simple and effective way of implementing the main loop program.

The previous design’s code flowcharts were a good starting point for their final software implementation. They clearly defined sensor input triggers and appropriate decisions based on those inputs. They did not mention if their decisions or actions were a result of Level1 requirements, but it looks like they carefully planned out all of the necessary decisions the Pathfinder would have to make based on the terrain and lap objectives.

 

Discussion based on New Level 1 & 2 Requirements:

For the MCU Subsystem and Control Firmware section of the Electronics & Control Division, I will have to: 1) write the firmware required to translate commands from the tango tablet into control signals to the motors and servos in order to move the Pathfinder or move the pan and tilt field of view for the Google Tango, 2) Read sensors such as wheel decoders and translate into data bytes for calculating speed and distance to travel, and 3) implement control algorithms for controlling the charging of the Pathfinder’s solar panel charging network.

In order to code for tasks 1 and 2, I will reference and then modify the Pathfinder Code Flowcharts created by a past semester’s blog posting. I will also reference previously uploaded code for the Pathfinder that is available on GitHub from the Arxterra website.

Lastly, in order to code the algorithms for measuring and controlling the charge of the battery via solar panels, I will have to do further research on safe charging procedures and requirements and battery protection. I hope to have a scaled version of the Pathfinder available for prototyping and testing of the control firmware before final implementation to the final design.

Based on previous code for the Pathfinder, some of the level 2 requirements will have to be modified or deleted. For Example, our design will incorporate the Google Tango so there will be no need for obstacle avoidance measures and sensors since our design won’t be autonomous as it was defined as a level 1 requirement that the Google Tango is to act as a remote control with field of view. Examples of some of the code that I will have to tailor to our design are the programs written to measure battery consumption, drive the motors, and drive the servos. Programs that I might have to develop are charge controlling algorithms to safely charge and discharge the Pathfinder’s battery cells for optimal usage as define by the level 1 requirement needing the Pathfinder to be able to spend a day exploring the Amboy Crater.

A few of the programs previously written for the Pathfinder have not been uploaded or tested, so it will be crucial for me to start testing and debugging algorithms that are available on GitHub to determine which ones are viable and which ones I will need to code myself. It will be important for me to have working knowledge of how to code and upload programs onto the Arduino Board, so I will attend any and every training session that the Electronics & Control Division Manager hosts in order to continue to move this project forward. The Previous Design utilized an Arduino Mega so I will have to research on similarities and differences between the Uno and the Mega and see which one would be a better level 2 requirement solution.

 

Design and Manufacturing Research Work

By: Lindsay Levanas

Source Material

  1. Pathfinder Preliminary Project Documentation, Project Requirements 1. Sealed pan and tilt camera platform for an Android phone, pg. 3-4, 11/12/14 http://arxterra.com/pathfinder-preliminary-project-documentation/
  2. Pathfinder Preliminary Project Documentation, Project Requirements 2. Sealed environment for microprocessor and electronic components, pg. 4, 11/12/14 http://arxterra.com/pathfinder-preliminary-project-documentation/
  3. Pathfinder Preliminary Project Documentation, Project Requirements 5. Must be able to safely traverse mountainous terrain and avoid obstacles, pg. 5, 11/12/14http://arxterra.com/pathfinder-preliminary-project-documentation/
  4. Pathfinder Pan and Tilt Camera Platform, Theory, 10/26/14 http://arxterra.com/pathfinder-pan-and-tilt-camera-platform/
  5. Pathfinder Pan and Tilt Camera Platform, Procedure, 10/26/14 http://arxterra.com/pathfinder-pan-and-tilt-camera-platform/
  6. Pathfinder Preliminary Project Documentation, Major Project Elements 1. Sealed pan and tilt camera platform for an Android phone, pg. 7-8, 11/12/14 http://arxterra.com/pathfinder-preliminary-project-documentation/
  7. Pathfinder Preliminary Design, 11/12/14 http://arxterra.com/pathfinder-preliminary-design/
  8. Pathfinder Preliminary Project Documentation, Major Project Elements 2. Sealed environment for microprocessor and electronic components, pg. 8, 11/12/14http://arxterra.com/pathfinder-preliminary-project-documentation/
  9. Pathfinder 3D Printing, Introduction, 12/11/14 http://arxterra.com/pathfinder-3d-printing/
  10. Pathfinder Custom PCB Design, Background, 11/11/14http://arxterra.com/pathfinder-custom-pcb-design/
  11. Pathfinder Preliminary Project Documentation, Major Project Elements 5. Must be able to safely traverse mountainous terrain and avoid obstacles, pg. 10, 11/12/14http://arxterra.com/pathfinder-preliminary-project-documentation/
  12. Pathfinder Custom PCB Design, Schematic Components, 11/11/14 http://arxterra.com/pathfinder-custom-pcb-design/

 

Introduction

During the fall of 2014, the first Arxterra Pathfinder project was outlined and implemented. The basic concept was to mirror Mars rovers, both in their basic construction and autonomous ability. To this end, requirements were created to help guide the original designers in building a simplified Earth base model. Now, during the spring of 2016, a new group of engineers will work together to build upon the previous Arxterra Pathfinder project to bring it closer to the rovers that have been sent to Mars. Following below is a review centered on the design and manufacturing elements of Pathfinder’s requirements as discussed in its original documentation. The review will consist of the evaluation and modification of previous requirements to encompass the new project goals to implement Google Tango and solar panels in the current Pathfinder model, as well as new requirements where necessary.

 

Review of Pathfinder’s 3D simulated sealed pan and tilt camera platform for an Android phone requirement

Pathfinder’s first original requirement was to utilize a sealed pan and tilt camera platform for an Android phone.1 Using the dimensions of the Pathfinder’s base and the field of view measurement calculations from the Android phone’s camera, a design was selected and modeled.5 While the measurement requirements are quantitative, verifiable and realizable, the resulting 3D model of the pan and tilt platform is not, as not all measurement dimensions are given. The dimension of each piece is not defined, and so a working 3D model of this platform cannot be duplicated.  Located at the subsystem level (level 2), this 3D modeling requirement is linked to the project level (level 1) requirement for a sealed pan and tilt camera platform for an Android phone.6 With the proper measurements, this 3D model would move the design process forward, as materials for the parts could then be selected (by trade-off study, though this process is currently missing from Pathfinder’s documentation) and the final product could be constructed on Pathfinder’s base.

For the spring 2016 Pathfinder project, the above requirement and it’s subsequent requirements, trade-off studies, and measurement calculation process will not change much accept to accommodate a Google Tango tablet as the camera, instead of an Android phone. Also, as the 3D model of the pan and tilt platform is not clearly defined, a trade-off study of different designs and their measurements will be done.

Lastly, a new sublevel requirement will be added to account for temperature control of the sealed pan and tilt platform.

 

Review of Pathfinder’s 3D simulated preliminary design requirement

Another of Pathfinder’s project level (level 1) requirements was to create a sealed environment for the microprocessor and electronic components.2 Therefore a subsystem (level 2) requirement to 3D model the sealed environment was created.8 However, unlike the pan and tilt platform, the sealed environment for the electronics wasn’t modeled alone. Instead, both sealed environments were 3D modeled together with the body of Pathfinder to create the preliminary design requirement.7 As this design features 3D modeled pictures only, it is qualitative and not verifiable or realizable. Also, while the 3D modeled sealed environment for the electronics is linked to one of the project requirements, the Pathfinder 3D model as a whole is not. Therefore, it should be worded such that it encompasses the other two sealed environment requirements and should replace them as a project level (level 1) requirement. The sealed pan and tilt camera platform for an Android phone requirement, and the sealed environment for the microprocessor and electronic components requirement should then be redefined as subsystem (level 2) requirements so that the link back to the project level (level 1) requirements is easily traceable. Placed in this order, the preliminary design requirement would move the design forward, as then the subsystem requirements for the sealed environments would naturally follow. Finally, note that there are no links to source material and that no equations are used to calculate the initial set up for the preliminary design requirement.7

Similar to the 3D simulated sealed pan and tilt camera platform for an Android phone requirement, the 3D simulated preliminary design requirement is lacking in measurements and design trade-off studies. However, as the spring 2016 Pathfinder project will incorporate a Google Tango tablet and solar panels in its design, different structural trade-off studies then those mentioned to be missing will be conducted to account for the new design conditions.

Lastly, a new sublevel requirement will be added to account for temperature control of the sealed environment for the microprocessor and electronic components.

 

Review of Pathfinder’s 3D printer requirement

Based on the original documentation, the 3D printing of the sealed pan and tilt camera platform for an Android phone is a subsystem (level 2) requirement.9 As measurements are not given, the 3D printer requirement is qualitative only, and not verifiable or realizable. Had this requirement been listed under the project level (level 1) requirement of making the sealed pan and tilt camera platform for an Android phone, it would have been a subsystem (level 2) requirement, but it was not. 3D printing was however mentioned under the project level (level 1) requirement to make a sealed environment for the microprocessor and electronic components,8 but then there is no documentation on that manufacturing process. Both of the project level (level 1) requirements mentioned should contain 3D printing as a subsystem (level 2) requirement to help link the two levels together. No links to source material are mentioned, though one about the quality expectations of 3D printers would help. Such a source would allow for a more realistic and detailed requirement. Providing the quality of the 3D printed sealed pan and tilt camera platform for an Android phone is high, this requirement moves the design forward in that it may now be integrated onto the body of Pathfinder. Also, although none are mentioned, this requirement is based on the 3D simulation’s measurements and dimensions.

 

Review of Pathfinder’s Custom PCB Design requirement

As there is a project level (level 1) requirement for Pathfinder to safely traverse mountainous terrain and avoid obstacles, it follows that there is a subsystem (level 2) custom PCB Design to limit the amount of wires in the open.10, 11 Though a qualitative requirement, it is still both verifiable and realizable. No links to source material is listed, however there is both a picture and pin assignment chart included in the document, making it possible to replicate and verify the PCB design requirement.12 Slimming the electronic components on to a PCB moves the design forward to meet its project (level 1) requirement of safely traversing mountainous terrain and avoiding obstacles.3

For the spring 2016 Pathfinder project Google Tango will be used instead of the Android phone’s camera, GPS system, and sensors. In addition, Solar panels will be used to charge the batteries, therefore powering Pathfinder’s system. Both of these features will be implemented into the PCB while their previous counterparts are removed. As such, a different PCB board will be used based off of the new schematic that the electronics and control engineer (PCB Design) will design.

 

Conclusion

Pathfinder’s design and manufacturing will include 3D simulated models of Pathfinder as a whole, of the sealed pan and tilt camera platform for a Google Tango tablet, and of the sealed environment for the microprocessor and electronic components. From these models, parts may be either 3D printed or purchased. Finally, a custom PCB run by solar panels will be assembled.

 

Creativity Exercise:

Problem Statements:

  • Weight requires more current to run than solar panels can easily provide.
  • Runs on batteries, not solar panels. How and where can solar panels be fitted to Pathfinder?
  • Battery for Tango Tablet can only last about 45 minutes. How are we going to charge it constantly?
  • Cooling system for electronics. How do we keep the electronics from overheating?

 

 

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