Spring 2017 Mini Pathfinder Final Blog Post

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 By: John Her (Project Manager)

Moses Holley (Electronics and Control)

Edgardo Villalobos (Manufacturing-Solar Panel)

Johnathan Chan (Manufacturing-Chassis)

Adan Rodriguez (Mission, Systems, and Test)

Table of Contents

Executive Summary

Project Objectives

The Mini Pathfinder project for Spring 2017 is a scaled and modeled after NASA’s 1997 Sojourner rover of the Pathfinder mission. It will utilize the 3Dot board and a custom PCB. It is to be remotely operable with a fully functioning rocker bogie suspension system. It will be able to provide speed and battery telemetry to the user via the arxterra app and have a solar panel that charges the battery.

Mission Profile

Our mission is a scaled version of the Pathfinder project. We will remotely traverse a course of 27.8 meters in length. The course will have 3 stairs it will descend and 3 stairs it will ascend with each stair being 27mm. During this course the Mini Pathfinder will demonstrate electronic differential turning, solar charging, proper rocker bogie mechanics and provide telemetry.

System Design

The Mini Pathfinder will use the 3Dot and a custom PCB for the extra motors and the encoders.

Figure 1. System Block Diagram

Subsystem Design

Modeling Results

Spring 2017 Mini Pathfinder Motor Trade Off Study

Spring 2017 Mini Pathfinder Solar Cell Voltage Test

Spring 2017 Mini Pathfinder Rotary Encoder Tradeoff Study

Spring 2017 Mini Pathfinder Motor no Load Current and Voltage Test

Spring 2017 Mini Pathfinder Bogie Degrees of Freedom

Spring 2017 Mini Pathfinder Encoder Testing

Interface Definitions

We have three interface definitions for three different IC’s. The first is for the 3Dot board. The next two are for the custom PCB that will have the two extra motor drivers and the digital io expander for the rotary encoders.

Figure 2. Interface Definitions for the 3Dot Board

Figure 3. Custom PCB IC Motor Driver Interface Definitions

Figure 4. Custom PCB IC Rotary Encoders Interface Definitions

Cable Tree

Our cables will be routed from the motors and encoders through the suspension and into the electronics box. The solar panel will have a mount with a hole where the cable will connect so that it can charge the battery.

Figure 5. Cable Tree

Mission Command and Control

Figure 6.

Figure 7.

Electronics Design

After the trade off studies, we have decided on micro metal gear motors and hall effect sensor based rotary encoders. To control the extra motors not connected directly to the 3Dot, we will be using a custom PCB that is base on the adafruit motorshield which houses a PCA9685 and two TB6612FNG motor drivers. In addition to the motorshield, we will also implement a MCP2301 I/O expander to take the digital input from the rotary encoders. The power for the extra motors will be supplied from the battery boost on the back of the 3Dot board so that we can access the same voltage that is supplied to the motors on board the 3Dot.

Figure 8. Adafruit Motorshield (PCA9685)

Figure 9. Adafruit Motorshield (TB6612FNG)

Firmware

After discussing our project flow chart with an fellow Electronics and Control Engineer, Forest Nutter, we decided to redesign our flow chart. The initial image is the beginning stages of an overall view of the project.

Figure 10. Firmware Flowchart

PCB Schematic

Since the 3DoT only has a single motor driver chip that is capable of driving two motors, we needed to make a custom PCB to interface with the 3DoT that will allow for 4 additional motors and also be able to take digital input for the rotary encoders. We modeled the motor driver off of the adafruit motor shield version 2.3. The motor shield consisted of the PCA9685pw PWM driver and two TB6612FNG dual motor drivers, which is what the 3DoT uses. The PCA9685pw allows for control of PWM outputs through the I2C bus, which is available through the 3DoT, so that we could properly control the motor drivers. For the digital IO expander, we chose the MCP23017 due to it having 16 digital IO channels for our rotary encoders, which use two digital outputs per wheel for a total of 12 outputs.

Figure 11. Custom PCB Schematic

Our first schematic design had many errors that were easy to point out and a few that were only seen if looking very close. Fabian, previous EE 400D student, pointed out the schematic flaws and  gave recommendations. One of the mistakes I made was in forgetting the pull up resistors for the I2C communication. The I2C needs the pull up resistors because most of the devices are active low. Throughout my ICs and the voltage in, (VCC and VBoost), I forgot to place decoupling capacitors for circuit protection and for clean signals. My first completed schematic looked great with labels on the wires. By simply clicking the name of the wire and looking closely, I connected the TB6612FNG dual motor driver outputs to each other which caused them to short. My project manager, Jon Her, advised that we start from scratch. After the irritative process the above image is the finish schematic. It was a tough process, but having the schematic looked over and over ensured that we have a potential working PCB.  

PCB Layout

After the electronics and controls engineer(ENC), was finished with the schematic on EagleCAD, it was suggested that we try to make a printed circuit board(PCB) out of it and mount the PCB onto the 3DoT board like a “shield” because it was a level 2 requirement(See Figure 1). On the EagleCAD, requirements for the power lines had the size of 16mil. Data routes had 10mil. And there was a 20 drill size for vias. All of the lines had a 45 degree turn so that it doesn’t lose its connection when it is printed and powered up. The top and bottom planes of our PCB are ground copper poured planes. After placing all of the parts on the specified size of the layout, we made sure we used the DRC several times to make sure it completed all the requirements. We also ordered the parts and components before the PCB was made, so that it would arrive in a timely manner.

 

Dimension on 3dot board

Figure 12. Dimensions of the Custom PCB Shield

 

Completed PCB Design

Figure 13. Screenshot of the Routing Diagram

Figure 14. Final product with top and bottom ground copper poured planes in red and blue

We created a custom PCB for our 3Dot board(see figure 3). After we did a final DRC on our final PCB, we then sent it to the president, customer, and Fabian for approval. We had to revise our board several times before it was approved, but once it was, it was sent to 4PCB to be manufactured. We then purchased the stencil from OshStecil. The next steps are to use the stencil and put solder paste on the top layer of the custom PCB. Then we will put the parts and components in its respective places. After, we will heat the board up using a heat gun so that the components will attach onto the board.

Hardware Design

Chassis

To ensure that the 3Dot sat correctly into the chassis, small cutouts were made to allow the Bluetooth module room along with a few pins that were sticking out from the battery holder. A channel was also cut out to allow a wire to access the battery boost on the underside of the 3Dot. There were also channels cut out to allow access to the usb port and the power switch on the 3Dot.

Figure 15. Inside the chassis

To allow proper rocker bogie mechanics, a three beveled gearbox was utilized. Each gear has 16 teeth to allow for a 1:1 gear ratio from the left side of the suspension to the right side.

Figure 16. The rocker bogie gearbox

Solar

As a requirement, the Mini Pathfinder was to have a Solar Panel charge the battery on the 3dot board. To accomplish this, the solar panel needed to be scaled to the rover, while also being able to supply enough voltage and current. The solar cells also needed to be encapsulated. The model of the solar panel was closely modeled after the Sojourner Rover.

Figure 17. Solar Cell on the Mini Pathfinder

With the help of the chassis manufacturer for the mini pathfinder, we were able to scale the size in which the solar panel needed to be. The model was scaled using schematic renderings of the real Sojourner that were found on the internet. The size of the solar cell needed to be around 122x52mm.

Once the size of the panel was found, I needed to find solar cells that were able to charge the 3dot battery and that would fit that size and then encapsulate them. To meet this, I used a 5V 200mA already encapsulated cell that was bought in store. The size of the solar cell was 120x70mm, which fit the requirement of size.

Figure 18. 120x70mm 5v 200mA Encapsulated Solar Cell

 

A micro usb was attached to both the positive and negative leads of the solar panel.

Figure 19. Wiring Diagram

 

After finding the type of solar cell I’d be using, a way of holding the cell onto the rover needed to be found. Using Solidworks, I was able to create a holder to house the cell in place with a hole in the bottom to allow for the micro usb plug to pass through to connect to the 3dot board through the outside. This holder allowed for easy replacement of the cell, if needed. The cell could easily be removed by sliding in and out.  

Figure 20. Solar Cell Holder

Figure 21. Solar Cell in Holder

In conclusion, the solar cell needed to be tested more in order to observe how long it really took to charge the battery. Overall the solar cell was a success in looks and functionality as far as charging.

Verification & Validation Test

Verification and validation can be viewed at this link.

https://drive.google.com/open?id=1D4-kNlP_zy35XqHd-88Zd2Wl2X3w6gr05WJnChsNDzU

Project Status

Power Allocation

Figure 22. Power Allocation based on maximum battery current discharge at any given time.

Mass Allocation

Figure 22. Mass allocation

3d Print Allocation

Figure 23. 3d Print time allocation

Cost Report

While we were able to get many parts and pieces for free, what cost the most was the custom PCB parts and the rotary encoders.

Figure 24. Costs of the project

Burndown and Percent Complete

With all our tasks still left to finish and the progress we made on the project. We finished at %62 completion and remained behind schedule.

Figure 25. Project Burndown with completion at 62%

Concluding Thoughts

If there is anything I would change knowing what I know now, it would to ensure that progress is made consistently every week and that the project schedule be updated at every opportunity. Meeting up with Professor Hill is always a good idea as well. He has valuable input, and tries to help. The lectures may not cover everything but that is why there is so much documentation on Professor Hill’s website. I would also suggest reading over all the material and not taking any other classes that require a lot of time, as this class will already eat up all your time.

Project Resources

Project Video: https://youtu.be/HVbv6seOrCA

 

CDR:https://drive.google.com/open?id=1jm68b_I-lYIxEX2KnLQ9umSzJKdmA3KJs0HE2ciRDsY

PDR:https://drive.google.com/open?id=1ROLFfi2FNQnKXeBWZFecfNi36JnrB8bCFhlLQb2EYzE

Project Libre:https://drive.google.com/open?id=0BwLPwnTqIptrcWEwalpwLS1oVzA

Burndown:https://drive.google.com/open?id=0BwLPwnTqIptrWHE0c3lnbHEtYnM

Verification and Validation:https://drive.google.com/open?id=1D4-kNlP_zy35XqHd-88Zd2Wl2X3w6gr05WJnChsNDzU

Solidworks:https://drive.google.com/open?id=0BwLPwnTqIptremdfTTRaNkY5bFE

Fritzing Files: https://drive.google.com/open?id=0BwLPwnTqIptrc2xkWm5tYVdiM0U

EagleCAD:https://drive.google.com/open?id=0BwLPwnTqIptrM1pZbllodXVnbnM

Arduino Firmware: https://drive.google.com/open?id=0BwLPwnTqIptrQldiNFI1cDg3cW8

 

 

Spring 2017 Mini Pathfinder Encoder Testing

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By: Moses Holley (Electronics and Control)

Table of Contents

Introduction

The objective of this test was to gain an understanding of how RPM encoders work along with the Arduino code to manipulate them. We need the shaft encoders to detect wheel slippage and control the differential turning for the Mini Pathfinder.

Subsystem Relation

The RPM encoder test was first implemented using the OSEPP Motor Encoder. In this test, We gained an understanding of how the two A3144 hall effect sensors on the chip detect the rotating magnets. Then with the Arduino code converts the rotations in to RPMs. This test was used to measure the speed at which the wheels will turn at the 3dot output voltage of 5 volts. The n20 motors are rated at 6v at a speed of 32 rpm. We used an Arduino Uno because the 3Dot was having trouble uploading at the time.

Figure 1. Test Setup

Figure 2. RPM output

Arduino Code

Average RPM reading Code: This code waits for 10 readings then gets the avg of the RPMs.

// read RPM and calculate average every then readings.

// This code was retrieved online and we manipulated the reading[index] to get the correct readings.

const int numreadings = 10;

int readings[numreadings];

unsigned long average = 0;

int index = 0;

unsigned long total;

 

volatile int rpmcount = 0;//see http://arduino.cc/en/Reference/Volatile

unsigned long rpm = 0;

unsigned long lastmillis = 0;

 

void setup(){

Serial.begin(9600);

attachInterrupt(0, rpm_fan, FALLING);

}

 

void loop(){

if (millis() – lastmillis >= 1000){  /*Uptade every one second, this will be equal to reading frecuency (Hz).*/

detachInterrupt(0);    //Disable interrupt when calculating

total = 0;  

readings[index] = rpmcount * 5.45;  /* Convert frecuency to RPM, note: this works for one interruption per full rotation. For two interrups per full rotation use rpmcount * 30.*/

for (int x=0; x<=9; x++){

  total = total + readings[x];

}

average = total / numreadings;

rpm = average;

rpmcount = 0; // Restart the RPM counter

index++;

if(index >= numreadings){

 index=0;

}

if (millis() > 11000){  // wait for RPMs average to get stable

 

Serial.print(” RPM = “);

Serial.println(rpm);

}

lastmillis = millis(); // Uptade lasmillis

 attachInterrupt(0, rpm_fan, FALLING); //enable interrupt

 }

}

 

void rpm_fan(){ /* this code will be executed every time the interrupt 0 (pin2) gets low.*/

 rpmcount++;

}

 

RPM Code: This code gets the RPM of each reading.

// read RPM

// This code was retrieved online and manipulated the RPM.

volatile int rpmcount = 0;//see http://arduino.cc/en/Reference/Volatile

int rpm = 0;

unsigned long lastmillis = 0;

 

void setup(){

Serial.begin(9600);

attachInterrupt(0, rpm_fan, FALLING);//interrupt cero (0) is on pin two(2).

}

 

void loop(){

if (millis() – lastmillis == 1000){  /*Uptade every one second, this will be equal to reading frecuency (Hz).*/

detachInterrupt(0);    //Disable interrupt when calculating

rpm = rpmcount * 5.45;  /* Convert frecuency to RPM, note: this works for one interruption per full rotation. For two interrups per full rotation use rpmcount * 30.*/

Serial.print(“RPM =\t”); //print the word “RPM” and tab.

Serial.print(rpm); // print the rpm value.

Serial.print(“\t Hz=\t”); //print the word “Hz”.

Serial.println(rpmcount); /*print revolutions per second or Hz. And print new line or enter.*/

rpmcount = 0; // Restart the RPM counter

lastmillis = millis(); // Uptade lasmillis

attachInterrupt(0, rpm_fan, FALLING); //enable interrupt

 }

}

void rpm_fan(){ /* this code will be executed every time the interrupt 0 (pin2) gets low.*/

 rpmcount++;

}

// Elimelec Lopez – April 25th 2013

 

Conclusion

Although we gained a lot of understanding of how the RPM encoder works we will not use this model for our design. The shape of the OSEPP encoder is catered to a DC motor placed of it to be very close to the rotating magnets. We will have a different design that has the DC motor encased in the wheel which requires that the rotating magnet rotate around the motor. When we decide what kind of encoder will be used there will be an updated blog post.

Spring 2017 Mini Pathfinder Bogie Degrees of Freedom

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By: Johnathan Chan (Manufacturing-Chassis)

Intro

Since the Mini Pathfinder has to be able to climb up stairs as large as the wheels, we need to ensure that the bogie suspension has enough of an angle to pivot to overcome the stairs. Measuring the angle of the pivoting bogie will help us determine if it can do this.

Measurements

We were able to measure the degrees of freedom by laying the suspension flat on a piece of paper and making a mark of where it is when it is flat. Then we marked where it is completely up. After we used a protractor to measure the degrees of freedom which is 87 degrees.

Figure 1. Flat on the Ground

Figure 2. Suspension all the way up

Figure 3. Angle of which the suspension from flat on the ground to all the way up

Conclusion

With the suspension we created, the rover will be able to maneuver through obstacles the size of its wheels.

Spring 2017 Mini Pathfinder Motor no Load Current and Voltage Test

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By: Moses Holley (Electronics and Control)

Introduction

In this test, I will be testing the n20 motors at various voltages. The motors are rated for 6 volts, but the operating boosted voltage on the 3Dot board is 5 volts. The battery is rated at 3.6 volts, should we tap directly into the battery, but is typically fully charged at 4.2 volts [1]. The discharge cutoff voltage is at 2.75 volts, but wanted to test it at a slightly higher output of 3 volts.

Figure 1. Applying Voltage to the Motor

Results

Figure 2. Voltage and Current Results

Conclusion

There is no significant change in the current draw from the different voltages on all the motors. Since the 3Dot motor connectors will use the 5 volts from the boost converter, we will most likely utilize the same voltage output so that all the motors will spin at the same rate. This is an easier solution than programming the onboard motors to spin at the same rate that the other motors.

References

[1] http://www.batteryspace.com/prod-specs/1389-RCR123A36.pdf

Spring 2017 Mini Pathfinder Rotary Encoder Tradeoff Study

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By: Moses Holley (Electronics and Control)

Table of Contents

Introduction

The objective of this trade off study is to select an electrical device that can detect RPMs for our motors. One way RPM detection is important for our project would be our wheel slip detection.

Subsystem Relation

On the subsystem level, there are many things that we hope to accomplish with rotary encoders. We would like to detect wheel slip, wheel has lost traction or free spinning in the air, for each motor. We would also like to use the rotary encoders within differential turning and the climbing algorithm.

In order to fulfill this requirement, we researched optical shaft encoders, magnetic shaft encoders, and even considered designing a custom shaft encoder PCB.

Optical Shaft Encoder

Pololu’s optical encoders are sensor boards and reflective wheels added to micro metal gear motors with extended back shafts. They have the option of a 3-tooth and a 5-tooth encoder that provides a 12 counts per revolution or 20 counts per revolution. These encoders output are direct photo-transistor outputs. [1]

Figure 1. Optical Encoder

 

Magnetic Shaft Encoder

Similar to the optical encoder, Pololu’s magnetic encoders are attached to the extended shaft of an geared motor. These boards use 6-pole magnetic discs that can be used to add quadrature encoding. This board senses the rotation of the magnetic disc and provides a resolution of 12 counts per revolution of the motor shaft when counting the ends of both channels. [2]

Figure 2. Magnetic Encoder

Custom Shaft Encoder PCB

The custom shaft encoder was inspired by the magnetic shaft encoder just mentioned. The architecture is exactly like the shaft encoder. Although, after detailed research to find the exact EagleCad symbol for our hall effect sensor TLE4946-2K that the magnetic sensor uses. We discovered that the TLE4946-2K hall effect sensor can be with in TO-236-3, SC-59, SOT-23-3 packages. Digikey will send the package in SC-59. Fortunately, there are MOSFETs and Transistors that share similar packages. I choose PNP transistor that has a package of SC-59-BEC, SC59 (SOT23) Motorola, to be place holders for the hall effect sensor that we will purchase.

Figure 3. Magnetic Encoder Schematic and Layout

We were considering creating our own because we would have the ability to produce four from one square inch of PCB. The decision factor revolved around cost and time to have them implemented in our design.

Conclusion

In conclusion, we realized too late that we did not purchase the extended metal gear motors that would fit perfectly with the optical or magnetic shaft encoders. We decided to decline creating custom shaft encoders because they would be too time costly and we wanted to ensure that we had working encoders. We chose to purchase the magnetic shaft encoders instead. Although, we did not place the encoder behind the motor but inside a slit that held the motor attached to the suspension. We placed magnets on the inner wheel. As the wheel rotates the sensor should catch the change in poles from the magnet.

Resources

[1]https://www.pololu.com/product/2590

[2]https://www.pololu.com/product/3081

 

Spring 2017 Mini Pathfinder Solar Cell Voltage Test

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Solar Cell Blog Post

By: Edgardo Villalobos (Manufacturing-Solar Panel)

Introduction

The mini pathfinder will utilize one small encapsulated 5V 200mA solar cell. The reason for this is because it requires less cells to come up with the voltage and current required to charge the battery than if using the normal type cells, meaning less real estate on the small rover.

Results

The size of the solar panel for the Mini Pathfinder should be 122x52mm, but the size of the one on hand is 120x70mm. This cell will be connected through the usb port to recharge the battery on the 3Dot board.The measured voltage was 5.2V

Figure 1. Solar Panel Voltage

Conclusion

The voltage of this solar panel is enough to charge the 3Dot board through the usb port during operation. The next step will be to determine if the solar panel can output enough current.

Spring 2017 Mini Pathfinder Motor Trade Off Study

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By: Moses Holley (Electronics and Control)

Introduction

The objective of this trade off study is to find a motor that meets our robots requirements and also satisfies mission verification.

Subsystem Relation

Motor selection ultimately depended on the Mini Pathfinder’s size. Initially, the customer wanted a rover that could fit in one’s pocket and also in the palm of their hand. With this perspective we looked in to micro vibration motors. After a few meetings with the customer, we can to an consensus to have the Mini Pathfinder scaled down to 1:4.57 for length and height of the sojourner rover to minimally encompass the 3DoT Board. That in turn caused the wheel size to be 28 mm high and have the motors encased making the motor not visible.

Micro Vibration Motors

The vibration motors that we were interested in for our initial design can be seen here[1].  These motors require a gearbox to bring down the RPMs. Some of these motor RPMs were as high as 15000 RPM. In creating the gearbox we would have to alter the shaft and place the gearings on top of the shaft.

Figure 1. Micro Vibration Motor

Micro Metal Gearmotor HP 6V

The updated design scale granted to me to to choose a motor that must not exceed 19mm. The 19mm was given by the 2mm clearance of the 3D print of the wheels on top and bottom of the motor. The motors chosen has a 12mm diameter [2]. It also already had its own gearbox that produced 30 RPMs according to the specs. I figured this would be a great motor size just in case we make additional adjustments to the wheels. We later did make adjustments by adding shaft encoders. There was still enough clearance for the wheel and the shaft encoder.

Figure 2. Micro Metal Gear Motor

Conclusion

When choosing a motor for the Mini Pathfinder, we came to find out the size of the robot is a huge factor. Our first idea of the motor caused me to research for micro vibration motors. Those motors required many adjustments to benefit the Mini Pathfinder. Fortunately, we were able to resize our robot which actually granted us a motor that not only met clearances but also ideal performances through the assembled gearbox. After this trade off study, we decided to use the Micro Metal Gearmotor HP 6V motors for our design.

References

[1]https://www.digikey.com/product-detail/en/jinlong-machinery-electronics-inc/Z4TL2B124064X/1670-1016-ND/6009921

[2]http://www.ebay.com/itm/131747528794?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Spring 2017 Mini Pathfinder Updated Mission Profile

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By: John Her (Project Manager)

Introduction

The Mini Pathfinder mission has changed since the PDD where it will no longer participate with other robots in a game. Instead, the Mini Pathfinder will have the same mission as the Spring 17’ Pathfinder but scaled down.

New Mission Profile

We will remotely traverse a course of approximately 27.8 meters in length. The course will have 3 stairs it will descend and 3 stairs it will ascend with each stair being 27mm. During this course the Mini Pathfinder will demonstrate electronic differential turning, solar charging, proper rocker bogie mechanics and provide telemetry.  

Figure 1. Pathfinder distances in Red. Mini Pathfinder distances in blue

Since the Spring 2017 Pathfinder is inherited from the Fall 2016 Pathfinder, the distance from the center of the front wheel to the center of the rear wheel is a total of 19.22 inches or 488.188mm [1]. To get the scale factor, we find the distance from the center of our front wheels to the center of our rear wheels which has a measurement of 99mm. (488.188/99=4.9311919). We mapped the coordinates of the Spring 2017 Pathfinder and used google maps and its measuring tool to get approximate measurements.  

Conclusion

With the new Mission Profile set, we can continue with our design of the Mini Pathfinder.

References

[1]http://arxterra.com/the-pathfinder-fall-2016/#Hardware_Design

Spring 2017 Mini Pathfinder Size Calculations Update

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By: Johnathan Chan (Manufacturing-Chassis)

Intro

The size of the Mini Pathfinder will be determined by the size of the 3DoT board. The chassis should the the minimum size needed to encompass the 3DoT. Since the 3DoT has dimensions of 70mm in length and 35mm in width, we used this as part of the basis of our calculations. The other part of the calculations that we used are from the measurements from the patent drawings.

Calculations

The Sojourner rover patent files were found online and printed out. The drawings were measured and compared to the dimensions of the Sojourner rover found online. The measurements taken from the drawings were very close in proportion to the given dimensions of the Sojourner rover. The length and height of the Sojourner rover is 65cm x 30cm (650mm x 300mm) which gives a ratio of 2.167. The measurements of the drawing gave a length of 139mm and a height of 63mm which gives a ratio of about 2.21. This gives an error of about %2 ( [(2.21-2.167)/2.167] * 100% ≅ %2). Since only the overall dimensions of the Sojourner rover could be found, we used these patent drawings for the basis of our scaling of the electronics box (chassis). Comparing the given length of 650mm to the measured length of 139mm gives a scale of 4.68 for the patent drawings. The electronics box length is measured at 68mm and height at 29mm, this gives a ratio of 2.34. If we apply the ratio above for length to height (2.34), then we get a height of 30mm. So for the total scale factor for our Mini Pathfinder chassis for the length and height will be 4.57. We use the measurements taken from the patent drawings and get a scale factor of 6.87 for the width of the Mini pathfinder from the calculated dimensions.

Figure 1. Patent Image Measured

Using these scale factors, we can determine the size of solar panel we need as well with 560mm/4.57 ≅ 122.5mm for the length and 360mm/6.87 ≅ 52mm for the width. The dimensions for the wheels of the sojourner are 130mm in diameter. Using the scale factor the diameter of the Mini Pathfinder is 130mm/4.57 ≅ 28mm.

Preliminary Project Plan

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By Martin Diaz (Project Manager)

Adan Rodriguez (Mission System and Test)

Moses Holley ( Electronics and Control)

John Her (Manufacturing)

Edgardo Villalobos (Solar Manufacturing)

 

Table of Contents

WBS

By Martin Diaz (PM),

Adan Rodriguez(Mission,Systems)

 

The work breakdown structure organizes the work needed to complete the project by putting task under each engineer. For our WBS the work of the system engineer was organized into 3 blocks, System Design, Software, and system tests. The work of the ENC engineer was organized into 4 blocks, Electronic Design, Research/Experiments, Microcontroller and PCB, and finally MCU Subsystem and control. The work of the Manufacturing engineer was broken down into  5 blocks, Mechanical Design, Research, 3D simulations, and manufacturing parts and assemblies, and assemble Mini-Pathfinder.

 

Schedule

By Martin Diaz (PM)

The project schedule was created by using Project Libre. Each Task in the WBS was put as task into Project Libre and then the start and end dates were assigned. When a task depended on a other task to be finished first dependencies were assigned. This can be done by clicking and dragging arrows to other boxes. The program will automatically adjust the task.

Burndown

By Martin Diaz (PM)

The Burndown is a chart that shows how much work is left to complete the project vs time.  The Burndown was calculated by moving the task in the schedule to columns in excel and then assigning the percent completion for each task. The ideal percent completion and real percent completion were then plotted vs time.

Power Allocation

By Adan Rodriguez (Mission and Systems)

John Her (Manufacturing)

Moses Holley (ENC)

Edgardo Villalobos (Solar-Manufacturing)

 

The power rating for all of the components on the Power Allocation Report list were calculated using specification sheets of corresponding components. We approximated our mission duration to be 1 hour (one fourth the duration of the Pathfinder’s mission due to our rover being one fourth scale in size). Using the specification sheets to find current ratings of the components, we multiplied the current ratings by one hour to calculate power ratings in milliamp-hours. For the motor drivers, we looked at the power consumption of the IC and divided the operating voltage to get the current draw (0.78W/6V=130mA). The I2C I/O Expander is rated for output of 25 milliamps per pin and we will be utilizing 6 pins implying a total power consumption of 150 milliamp-hours. The Project Power Allocation was set to be slightly higher than the total Expected Power. Note that the Project’s Power Allocation value was used to aid in determining which battery to choose for our mission.

Mass Allocation

By Adan Rodriguez (Mission and Systems)

John Her (Manufacturing)

Moses Holley (ENC)

Edgardo Villalobos (Solar-Manufacturing)

 

Estimates of the 3Dot Board and Custom SMD Board were based off the fact that they are similar in size to the Raspberry-Pi Board (31 millimeters x 66 millimeters). The chassis, solar panel and suspension system were weighed with a scale. Corresponding Sources of expected weights is provided under the Source column. The Project Mass Allocation was set to be slightly higher than the total Expected Weight.

Cost Allocation

By Adan Rodriguez (Mission and Systems)

John Her (Manufacturing)

Moses Holley (ENC)

Edgardo Villalobos (Solar-Manufacturing)

 

The current battery that we intend to buy may be switched out for a different battery after the Mini Pathfinder is built and tested for its power efficiency. About one third of the products that will make up the Mini Pathfinder will be free of charge due to our team members already possessing certain products. Corresponding sources of expected pricing is provided under the Source column. Because the Mini Pathfinder didn’t have a cost requirement the Project Cost Allocation was set to be slightly higher than the total Expected Cost.