Rocker-Bogie Suspension System

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By: Adolfo Jimenez (Manufacturing)

Verified By: Jordan Smallwood (Project Manager)

Approved by: Miguel Garcia (Quality Assurance)

Table of Contents

Introduction:

In order to mimic the suspension capabilities of the rovers sent to Mars by NASA, our rover will incorporate the same rocker bogie suspension system utilized by the Mars rovers to traverse an extreme desert-like terrain. This suspension system, introduced with the original Mars Pathfinder project, is the same design preferred by NASA for nearly all the Mars rovers. The main advantage of this type of suspension system is that the load on each wheel is nearly identical and thus allows an equal distribution of force regardless of wheel position. Taking into consideration the harsh terrain found on Mars this type of suspension system provides a better alternative to that of the common 4-wheel drive soft suspensions found on most automobiles.

Figure 1: View of Differential Gearbox System without Box

Design enhancements:

For our project, since we are mainly building upon the design of previous semesters, we can utilize the things they did correctly and build upon things they may have overlooked. The main design difference, as it pertains to the suspension system, is the addition of a differential gear box. Whereas previous semesters utilized a barely functioning differential bar, or no differential at all, this semester we decided to remove the bar entirely and replace it with a much more functional differential gear box. This addition of a differential gear box will offset the wheel assemblies by about .8 Inches on each side and raise the main platform about .38 inches higher from the ground. Upon further research of rover suspension systems our group discovered a helpful blog on a website called Beatty Robotics. The website provides many helpful blogs describing the design and creation process for many custom Mars rovers and other robots. The particular blog post that helped us meet our needs pertained to a differential system used for a custom Spirit II Mars rover. Feedback on the blog pertaining to the parts used lead us to the website McMaster-Carr where we were able to order the parts to assemble our own Differential.

Suspension- Wheel Assembly:

Figure 2: Wheel Assembly

The wheel assemblies contain a total of 6 wheels with a symmetric build for both sides. Each side contains 3 wheels which are connected to each other by two links. The main linkage called the rocker has two joints, one affixed to an axel forming the differential mechanism and the other connected to the remaining two wheels. This linkage from the rocker to the other linkage between the two wheels is known as a bogie (hence the name rocker bogie). To go over an obstacle, the front wheel is forced against the obstacle by the center and rear wheels. The rotation of the front wheel then lifts the front of the vehicle up and over the obstacle. The middle wheel is then pressed and pulled against the obstacle by the rear and front wheels respectively until the wheel is lifted up and over the obstacle. Finally, the rear wheel is pulled over the obstacle by the front two wheels.

Suspension- Differential Gear Box:

Figure 3: Differential Gear Mechanism Close-up

The differential is composed of three identical beveled gears situated 90-degrees from each other at the center of the rover. Each gear is affixed to a 6-inch steel drive shaft that is mounted to the rover body by 2 mounted sleeve bearings. One gear connected to the left, one gear connected to the right, and the last gear assembled onto the main platform. The two rods facing opposite of each other on the left and right of the robot help serve as axels for the wheel assemblies. The axils are connected to the wheel assemblies by 2 parallel aluminum tubes that make up the rocker bogie suspension system. The inclusion of this differential insures that the robot’s body and pitch angle are always adapted even if one side of the rover steps over an obstacle. If one leg goes over an obstacle, an opposite force is applied to the other leg. So, if one leg goes up, the other leg goes down. This downward force onto the opposite leg helps the robot maintain traction in the leg assembly that is still on the ground. The way this works is when one side changes in pitch, say for instance one side begins climbing over an obstacle, this mechanism rotates the main body around the rocker joints by the average rotation angle of the two sides. For this differential mechanism, all gear ratios are the same. That means if the left gear rotates 10 degrees and the right gear rotates 20 degrees, the main platform will rotate 10 + 20 = 30/2 = 15 degrees or the averaged amount. This keeps the main box more level (less tilted) than it normally would be when going over large, uneven obstacles.

References:

  1. https://www.arxterra.com/2016-pathfinder-design-and-manufacturing-rocker-bogie-suspension-system-design/
  2. https://www.arxterra.com/news-and-events/members/pathfinder/pathfinder/pathfinder-generations/pathfinder-generation-4/
  3. https://en.wikipedia.org/wiki/Rocker-bogie
  4. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.538.6955&rep=rep1&type=pdf
  5. http://beatty-robotics.com/differential-for-mars-rover/
  6. https://www.mcmaster.com/

Pathfinder Preliminary Design Blog Post – Spring 2018

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By: Jordan Smallwood (PM), Diane Kim (E&C), Mohammad Yakoub (MST), Adolfo Jimenez (Manufacturing)

Approved by: Miguel Garcia (Quality Assurance)

Table of Contents

Project Overview

By Jordan Smallwood

Project Objective:

The Pathfinder is a project that has been passed down from generation to generation. The originators built the chassis and original idea back in the fall semester of 2016. A rover like this does not make its way into the EE department that often since the lot of us don’t typically have much experience with welding and fabrication. Luckily enough for our group we will be picking up the slack where the previous teams had left off. It seems as though every semester that attempts this project faces failure in one way or the other whether it is the differential rocker-bogie mechanism or leaving wires exposed to short the 12V golf cart battery. Either way, the overall aim of this project is to finally finish what other groups have started and that will be defined in the following sections of this report.

Mission Objective:

By Jordan Smallwood

The Spring of 2018 Pathfinder will follow the path laid down by previous Pathfinders. The mission will begin in front of the CSULB library where the rover will exit its cocoon state. The rover will then proceed to begin its journey through campus, a 0.09 mile journey to its charging station. There will be 10 predefined GPS checkpoints along the way and the rover will traverse a flight of stairs. Once the rover has arrived at the charging station it will begin to track the sun and provide the Arxterra user with up to date battery level conditions. Specifically the Pathfinder will demonstrate the following:

  • Custom solar panels capable of tracking the sun and exhibiting optimum orientation so that battery charge takes the least amount of time.
  • The rover will be able to enter and exit a cocoon state. The term cocoon state implies that the solar panes will fold up so that in the event of a dust storm the solar panels will not become damaged. This state will be entered if the rover is in launch, a dust storm or whenever the rover is operating over steep terrain.
  • The rover will be able to communicate with the Arxterra app providing information like battery level, panel angles, panel voltages and charging current.
  • The solar panels will have a form factor identical to those of the Spirit and Opportunity Mars Rovers.
  • The rover will exhibit a 6-wheel slip differential for turning and traversing rough terrain. Since the robot will be climbing over random objects, some wheels will not require the same speed as other wheels and this needs to be considered while operating the rover.
  • Demonstration of GPS navigation with obstacle avoidance.
  • The course mapped out by F’16 and S’17 will be the same course for S’18.
  • There shall be no modification to the rover that stands in the way of high desert operation.

Project Requirements

By Jordan Smallwood

Level 1 Requirements

  1. The pathfinder will travel a 0.09 mile course. This course includes going up a set of 3 stairs at a 70 degree incline and another set of 3 stairs with a decline of 70 degrees.
  2. Pathfinder shall launch from a cocoon state
  3. The Pathfinder will enter and exit the cocoon state by Arxterra app user input.
  4. Pathfinder shall allow the user to enter the “articulate state” program module which will be available once the Pathfinder has exited its cocoon state. This sequence will direct the solar cells at the proper orientation to allow max charge of the battery.
  5. The Pathfinder will update the user with information about panel angles, GPS location, battery level and charge current when in the “Articulate state”.
  6. The overall solar panel system will consist of two side panels, a rear panel and a base panel.
  7. The solar panel design will be identical to those of the Spirit and Opportunity Mars Rovers.
  8. A 6-wheel electronic slip differential shall be implemented
  9. Wheels under a no-load condition will be considered and power to that motor will be decreased.
  10. The Pathfinder shall demonstrate obstacle avoidance while making its journey through campus.
  11. Any modifications made to the Pathfinder shall not inhibit the rover’s ability to operate in high desert condition.
  12. Rocker bogie mechanism shall be improved by implementing a differential gear-box system as opposed to the differential bar.

 

Level 2 Requirements

By Jordan Smallwood

  1. Course Duration
    • The power budget of our overall design will determine the duration of our course, once this has been completed the actual distance traveled will either be verified by this or will have to be changed to a shorter distance.
    • In order to travel up these stairs our mass report along with our motor mock up will verify that this can be accomplished.
  2. Cocoon Launch
    • To perform the cocoon state function the solar panels will be mounted to worm gears attached to DC stepper motors to ensure smooth operation.
  3. Enter/Exit Cocoon State
    • The Pathfinder shall communicate via Bluetooth with the Arxterra user and will have an interface allowing the user to enter/exit the cocoon state.
  4. Articulate State
    • The articulate state module will adjust the positions of the solar cells using a proportional controller.
    • The proportional controller will accept the charge rate as an input and will output changes in orientation.
  5. Telemetry
    • While communicating with the user via Bluetooth on the Arxterra app the Pathfinder shall respond with packets of information related to this information.
  6. Solar Panels
    • These four panels will be constructed of aluminum such that the rover can operate in the harsh desert conditions typical of Mars.
    • The side and rear panel’s will be capable of position orientation to enter and exit the cocoon state and also optimize battery charge
  7. Solar Panel Form Factor
  8. 6-Wheel Electronic Slip Differential
    • A coded differential will be used ensuring that the wheels are spinning at the same rate.
    • IR range sensors will be mounted to the motors to determine the velocity of the wheels
    • Current sensors will be used to determine the load on the wheels
  9. No Load
    • To conserve energy, the rover will stop rotation of a freely moving wheel using the current sensors
  10. Obstacle Avoidance
    • Ultrasonic sensors will be used to determine if an obstacle is in its path.
    • An obstacle avoidance routine shall be implemented.
    • The rover will not make any attempt to climb an object that it is unable to clear
  11. Modifications
  12. Rocker-Bogie Mechanism
    • The differential gear box will be constructed of three miter gears, three machined shafts, six mounted bearings and shaft collars
    • This mechanism will be mounted below the Pathfinder and enclosed in an aluminum box with the electronics.
    • This box shall be easily removed for inspection and maintenance.

 

Work Breakdown Structure

By Jordan Smallwood

Figure 1: Work Breakdown Structure for Pathfinder Project

Product Breakdown Structure

By Mohammad Yakoub

Verified By: Jordan Smallwood

Figure 2: Product Breakdown Structure for Pathfinder Project

 

Resource Reports

By Mohammad Yakoub

Verified By: Jordan Smallwood

Power Report:

Figure 3: Preliminary Power Budget

Mass Report:

 

Figure 4: Preliminary Mass Report

Cost Report:

Figure 5: Preliminary Financial Report

System Block Diagram

By Mohammad Yakoub

 

Figure 6: Preliminary System Block Diagram

 

Interface Matrix

By Jordan Smallwood

Figure 7: Preliminary Interface Matrix

Software Design

By Jordan Smallwood

  1. Obstacle Avoidance: In order to make sure that the Pathfinder does not fail the mission, ultrasonic sensors will be used in the front of the rover to verify that an object is not too large for Pathfinder to climb over. This routine will take place within the software and more information will be provided at a later time.
  2. GPS Checkpoint Navigation: Pathfinder will use GPS location information from the on-board iPhone or Android device and follow the course as defined in the mission objective. This will involve some type of digital controller and will be implemented in software. Again, these are preliminary concepts and not much has been constructed as of now but will be provided as the semester continues.
  3. Motor Functions: Pathfinder will perform very basic motor functions such as go straight, turn around, turn left, turn right and stop.
  4. Read Encoders: To determine the speed that each wheel is spinning this function will examine the current speed of each wheel by counting the pulse trains given from the IR sensors mounted to the wheels.
  5. Stop Motors Under No-Load: By examining the current associated with each motor we can make sure we are not spending energy for nothing. This will most likely be a conditional statement and if the current state of the motor is under a no-load condition, then the power supplied will be cut off. Reinitializing the motor speed once a load is present will have to be tested though.
  6. 6-Wheel Differential: When making a turn the speeds of each motor needs to be considered since they may be traveling along different paths but need to arrive at the destination at the same time. By examining the speeds of the motors we can modify the PWM signal applied to ensure that we are traveling smoothly.
  7. Exit Cocoon/Articulate Solar Panels: When the user decides to either exit or enter the cocoon/articulate state the microcontroller will apply the functions necessary to do so.

 

Fritzing Diagram

By Diane Kim

Verified By: Jordan Smallwood

Figure 8: Fritzing Diagram

The components inside the chassis contains the following: batteries (2), dual motor drivers (3), ultrasonic sensors (2), servos (2), IR sensors (6), motors (6), and the Arduino Mega 2560 (1). Unlike the previous version which only had 1 battery, we will be using 2 batteries to power up the motor to decrease the size. The ultrasonic sensors are used to navigate the rover. The IR sensors are to be placed beside the wheels to measure the RPM by toggling the signal whenever the spoke of the wheel passes by. The VNH2SP30 dual motor drivers is used to control the speed of the motors thus the wheels. The servos are used for the pan tilt. All the peripheral systems are connected to the Arduino Mega 2560 to input and output signals.

 

Mechanical Design

By Adolfo Jimenez

Verified By: Jordan Smallwood

2D Drawings (Dimensions all in inches):

Rear and Top Side View:

Side View (left):

Figures(9,10,11): 2D Layouts of Physical Structure

For the pathfinder project, since we are mainly building upon the design of previous semesters most of the dimensions and physical parts will remain the same. The main design difference for the time being is the addition of a differential gear box. Whereas previous semesters utilized a barely functioning differential bar, this semester, we decided to remove the bar entirely and replace it with a much more functional differential gear box. This addition of a differential gear box will offset the wheel assemblies by about .8 Inches on each side and raise the main platform about .38 inches higher off the ground.

Differential Gear Box

Figures(12,13,14): 3D Layouts of Physical Structure

Two planar aluminum tubes for the rocker boogie suspension system are connected to each other by a differential mechanism. When one side changes in pitch say for instance one side begins climbing over an obstacle, this mechanism rotates the main body around the rocker joints by an average angle of two sides. Gear A connected to the left, gear B connected to the right and gear C is assembled on the main platform. In differential mechanisms, all gear ratios are the same. That means if gear A rotates 10 degrees and gear B rotates 20 degrees, the main platform will rotate 15 degrees.

Verification and Validation Plans

By Mohammad Yakoub

Verified By: Jordan Smallwood

 

Figure 15: Verification and Validation Part 1

 

Figure 16: Verification and Validation 2

 

Test

By Mohammad Yakoub

Verified By: Jordan Smallwood

3.3.1 Final Run

Description: The Pathfinder will follow a course That is 0.9 miles in length. The course will includes going up a set of 3 stairs at a 70 degree incline and another set of 3 stairs with a decline of 70 degrees. The robot will start the course in a cocoon state and will deploy solar panels.

Test Environment: Outside the classroom

 

3.3.2 Proportional Controller

Description: The Pathfinder will adjust solar cells using proportional controller.

Test Environment:  Inside a classroom

 

3.3.3 Cocoon

Description: User will use the Arxterra App to enter and exit cocoon mode.

Test Environment: Inside a classroom

 

3.3.4 Articulate Mode

Description: The user will use the arexterra App to activate ‘articulate mode’, and receive feedback from the Arxterra App.

Test Environment: Outside the classroom

 

3.3.5 Weighting

Description: Placing the fully assembled Pathfinder on a weighing scale.

Test Environment: Inside a classroom

 

3.3.6 Scale  

Description: Goliath should resemble the ‘Spirit Mars Rovers’

Test Environment: Inside a classroom

 

3.3.7 Obstacle Avoidance

Description: The Pathfinder will avoid obstacles while running the final course.

Test Environment: Outside the classroom

 

3.3.8 Solar panels

Description: The Pathfinder solar Panels will be made out of metal and use a stepper motor

Test Environment: Inside a classroom

 

3.3.9 Feedback

Description: The Pathfinder will relay information charging panel angles, GPS location, battery level and charge current through the Arexterra App

Test Environment: Outside the classroom

 

3.3.10 Diff Gearbox

Description: The Pathfinder box will be made out of three miter gears, three machined shafts, six mounted bearings and shaft collars.

Test Environment: Inside a classroom

 

3.3.11 Diff Gearbox Case

Description: The Pathfinder Diff Gearbox will be enclosed in an aluminum box.

Test Environment: Inside a classroom

 

3.3.12 Mods

Description: The add modifications on the Pathfinder will hinder its ability to function on hard terrain.

Test Environment: Inside a classroom

 

3.3.13 RPM

Description: Use current source to measure the RPM of each wheel at different loads.

Test Environment: Inside a classroom

 Schedule/Planning

By Jordan Smallwood

 

Figure 17: Schedule Part 1

 

Figure 18: Schedule Part 2

 

Figure 19: Burndown Chart

References

  1. https://www.arxterra.com/pathfinder-s17-preliminary-project-plan/
  2. https://www.arxterra.com/spring-2016-pathfinder-preliminary-design-documentation/
  3. https://www.arxterra.com/the-pathfinder-fall-2016/
  4. https://www.arxterra.com/spring-2016-pathfinder-system-block-diagram-interface-matrix/

Making A Turn

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By: Jordan Smallwood (Project Manager)

Approved by: Miguel Garcia (Quality Assurance)

The pathfinder will be performing tank type turns, that is it will be pivoting about it’s center to adjust it’s orientation. This can be done by simply adjusting the direction of each of the wheel sets. For example, if you wanted to make a left turn you would do so by setting the right wheels forward and the left wheels backward.

Depending on where you would like to end up at the end of a turn you must consider the arc lengths that each wheel must travel to perform a certain turn. The pathfinder will be pivoting about it’s center point which is described by the following:

Figure 1: Derivation of soft differential speed ratios

By examining the above figure, we can see that motors 1, 3, 4 and 6 will be traveling along the same arc length. The only difference is that the set of motors 1 & 3 will be spinning the opposite direction of motors 4 & 6. Motors 2 & 5 will also be traveling along the same arc the only difference is the radius related to that arc is smaller than the other motor sets.

If we calculate the radii of each of the motors we can determine an appropriate motor speed ratio to pivot the pathfinder.

Figure 2: Calculation of Magnitudes

If we let MS1 be the speed of motors 1, 3, 4 & 6 and let MS2 be the speed of motors 2 & 5 then we can say the following:

Figure 3: Relating Motor Speeds

Now we know that in order to pivot about the center point we need to have MS2 = 0.545*MS1. In a perfect world all of our motors would be matched and the PWM signal to each would be identical and we could simply supply a PWM signal to each motor with that ratio in mind. However, this is not a perfect world and the load on each motor is constantly changing so instead we will need to monitor the speed of each wheel with simple encoders. Since our motors do not include encoders we will have to engineer our own. For our purposes this will be simple IR sensors strapped to the motors aimed at the spokes on our wheels. We could potentially purchase new motors that have included encoders prior to the gearbox so that we can achieve much better resolution but that will have to be a project for a later semester.

References

  1. https://www.arxterra.com/digital-slip-differential-voltage-ratio/

Spring 2018 Maze Definition

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By: Eduardo De La Cruz (SpiderBot PM), Ernie Trujillo (Goliath PM), Miguel Gonzalez (Biped PM), and Intiser Kabir (AT-ST PM)

Approved by: Miguel Garcia (Quality Assurance)

Table of Contents

Introduction

By: Intiser Kabir (Project Manager of AT-ST Walker)

 

We, the Project Managers for this Semester, are creating the initial design of how the maze will be structured so we can finalize the design of how our robots will be. The maze creates a limitation on how big our robots can be, how they can turn, ways to indicate an intersection, and types of sensors we can use. The maze we are redesigning must have the following: 3-way intersections, dead ends, and more than 1 path to finish including the shortest path. The shortest path must incorporate a right-hand rule for the robot as a fell safe, in case the robot doesn’t know how to detect intersections. We discuss how big the room size is for the maze along with either increasing or decreasing the size of the original design of the maze. We decide what type of material the maze should be, as well as a replacement for the current black lines. We also had to think what should be a backup method of navigating through the maze like a hedge follower. With all this information, we can finalize our robots’ design as well the methods of navigation through this maze.

Update 2: New Design (April 9, 2018)

     Color sensors will no longer be implemented for our projects due to a customer revision of the maze definition. According to the customer, since we plan on using UV sensors for our line following design, it would be more optimal to implement intersection detection using a UV grid. Also color sensing was out of the question for robots like biped or velociraptor whom would have difficulty reading RGB due to required placement position.

New Design

Figure 1: New Maze Design

As can be seen above, the maze design is a derivative of the maze design created by the Fall 2017 teams. All  dimensions to the maze itself have not changed, we just added 4’’ x 4’’ cross hatched UV lines across the whole maze floor.  The robot shall be able to detect if it is in a new room based on the intersection of two UV lines. UV lines will have a 1 cm or .393 inch line thickness which has been tested by Kris (Spiderbot E&C responsible for UV studies) for functionality.

 

Below is a file to the new Solidworks maze:

https://drive.google.com/drive/folders/1aZvnYXNC2wg36CWjMIFUWP1x0KuAyuNA

Printing of this maze can be done by converting the maze to a drawing.

Update 1 (March 15, 2018)

Things to take into account

By: Ernie Trujillo (Goliath PM)

 

When it came to creating the maze definitions there were certain aspects that needed to be taken into consideration before finalizing the maze. The project manager’s were in agreement of having all the robots navigate through the same maze to minimize the expense of manufacturing multiple mazes. The first, and most important, limitation that we had to consider was that the customer wanted the maze to fit into the front of room ECS 316 (this gave us a maximum of 8ft x 18ft). We decided to model a maze to the similar dimensions as the Fall 2017 semester. The maze that we have created will be 52in x 56in, with each room being 4in x 4in. Our choice for the room size was intended to accommodate the dimensions of the robots from both the morning and afternoon section. Currently, the dimensions of each robot are as follows:

  1. SpiderBot – 6in x 6 in (from leg-to-leg, but the body will fit within the rooms)
  2. Goliath – 5in x 4in
  3. BiPed – 4in x 2.5in
  4. AT-ST – 4in x 4in

When we were generating a maze, one aspect that we wanted to implement was situations similar to the ones from the EE 346 maze which were: (1) intersection to the left, (2) intersection to the right, (3) T-intersection, (4) left corner, (5) right corner, (6) dead end, and (7) hallway. Also, in the event that the sensor suite from a robot is inoperable, we added a ‘simplest’ path solution to the maze which the robot can navigate through to reach the finish. This is done by having the robot follow the wall to its right through the entire maze.

Design Ideas and the Reasoning Behind It

By: Miguel Gonzalez (MP: BiPed)

 

After noting all the information provided above it is clear that there are an infinite amount of possibilities in creating the maze. To reduce any redundancies and make sure all our set rules applied to our designed maze each project manager agreed that it would be best if every member creates a unique but adequate maze in which they are free to make their own design twists. These mazes are simply preliminary designs, once each member creates their design we will gather together and try to create a new maze that will implement each other’s maze while making sure all limitations have been accounted for.

We will begin by addressing the design ideas behind each preliminary maze drawings. The first maze we are going to take a look at is a design by Eduardo. According to Eduardo his main goal when designing the maze was to implement rooms that represented real life 4in by 4in rooms, and have a curved line following. As we can see from the image below Eduardo implemented an intermediate difficulty maze and did a good job in having turnarounds, 3-way intersections, curved UV lines, and even provided colored dots at the intersections. In terms of functionality, having curved lines in between room allows robots such as the Spiderbot and BiPed to have easier times detecting the UV lines while performing a turn. The colored dots in the intersections also allows each robot to detect when it has reached an intersection and thus knows when a turning action needs to occur.

Figure 2: Eduardo (PM- SpiderBot): Preliminary Maze Design

 

The second design was created by me. I started the maze by creating an aspect ratio that would easily scale to the 52in by 56in life-size maze. The rooms were also scaled to model the 4in by 4in squares. It is important to keep in mind the scaling of the maze, this is to prevent errors and delays when printing out the maze. I calculated the ratios and implemented them in Microsoft Excel, where the maze was designed. For the first designed maze, I had the idea of cutting off or leaving two corners out of the maze to act as START and END pads. This sections of the maze would ideally be used as a location for teams to place their robots and begin app control while having space for any adjustment/calibration movement. Overall two designs were created but the issue for both was that the maze was a bit difficult for robots to complete. The lack of additional paths to exit also prove to be an issue as the ideal maze would account for a simple path solution in which robots having a hard time responding to its sensor inputs can use.

Figure 3: Miguel (PM-BiPed): Maze with START and END zones

 

               Figure 4a: Miguel (PM-BiPed): Maze 2            Figure 4b: Miguel (PM-BiPed): Maze 2 Solution

      The final maze design was created by Ernie Trujillo. From Ernie’s design, we can see that the maze has 13 rooms across and 14 rooms vertically giving us a total of 182 rooms. Each room will be  4” x 4’’ and the width of the lines will be 1cm thick ~ .393 inch. The maze has more than one path to exit and Ernie made sure to make the shortest path one that would allow for right wall following in the event a robot’s intersection detection code fails. As can be seen below, the maze is scaled at a slightly larger size from the existing maze scale. This is due to the fact that the initial sketch Ernie designed was made to have a 52’’ x 56’’ scale (like existing maze), however, like Eduardo’s design, Ernie didn’t account for line width. As a result, the maze has to accommodate an additional 13 cm across and 14 cm vertically, resulting in the maze dimensions being approximately 57’’ x 61.5’’.

Figure 5: Ernie’s Maze (Goliath PM)

Final Design Decision

(by Eduardo De La Cruz – Spiderbot PM)

      Having had taken into account all the constraints, design ideas, and making sure that the maze would accommodate all off our designs. We as a group decided that Ernie’s design was the best choice in defining what the maze should look like. Unlike the other mazes’ Ernie’s maze provides a simple path (shortest path) for robots to exit implementing the right wall rule as a fail-safe. It also has more than one not overly complicating path to reach the exit, which is important when it comes to the time it will take to finish the mission. Additionally, Ernie’s maze incorporates multiple dead ends which will come in handy in the robot avoidance part of the mission, and has multiple 3 way, and T-intersections. Each room will be 4’’ x 4’’ and will incorporate both UV lines and colored dots for intersection detection.

A to scale model of Ernie’s maze was generated below by Eduardo using solidworks showing how  the maze would look if we were to print the maze. Solidworks files are included at the bottom of the post.

Figure 6: Final Design Maze

      As can be seen above, the total the size of the maze will be 57.5’’ x 61.86’’. Since each robot will have its own run, the maze was designed to have only one entrance and one exit. We decided to put a UV strip along the midpoint of the rooms with line thickness of 1 cm ~ .393 inch and with rounded edges of 1 inch in radius on every corner to improve turning angles. This means we will be implementing UV sensors for line following in our robots. The material we plan on using for the fabrication of the maze will be cloth. Cloth provides a more durable surface on which to apply the UV ink. Other surfaces such as paper may experience ink fading over time. In every intersection we plan on adding colored dots 1 inch in diameter to implement color sensing for intersection type.

 

Below is a link to the Solidworks files, as well as a template

https://drive.google.com/drive/folders/1aZvnYXNC2wg36CWjMIFUWP1x0KuAyuNA

 

 

Spring 2018 3DoT Hexy: 3D Print Times

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By: Raymundo Lopez-Santiago (Mission,Systems, and Testing)

Verified by: Eduardo De La Cruz (Project Manager and Manufacturing Engineer)

Approved by: Miguel Garcia (Quality Assurance)

 

Update: 04/17/18

After the first protype, the design was changed accordingly to fix issues identified from testing the robot (under stress). The new design has been sent to Ridwan and we are currently waiting for a response. A new table with the 3D print times will be updated later.

 

Introduction    

This blog post covers the overall 3D print time for parts used in the 3DoT Hexy robot. Eduardo De La Cruz (Project Manager/Manufacturing Engineer) has made a sketch and model for 3DoT Hexy in Solidworks. A preliminary 3D print time for 3DoT Hexy is determined using a 3D Print quote from the Long Beach Makers Society and Ridwan. The quote is for using PLA/ABS material. In Fig.1, print times for each part are shown as well as the total print time for all parts using the Long Beach Makers Society’s quote. In Fig.2, print times for each part are shown as well as the total print time for all parts using Ridwan’s quote.  As defined in the core level 2 requirements, 3D printing time shall not exceed the 6-hour limit. Each part should also not exceed a 2-hour limit of printing. At this moment we are planning to 3D print most of the parts needed in the project. We are not including any PCB housing in this print time estimate. The total print time estimated from the Long Beach Makers Society quote with the current design is 6.8 hours which exceeds the total 3D print 6-hour limit requirement. Only one part exceeds the 2-hour limit of 3D printing requirement per part and that is the bottom plate. Our initial plan to tackle both these issues was to pursue an alternative design to reduce the print time for the bottom plate and to manufacture the top plate using laser cutting instead of 3D printing which will reduce our total print time to 4.8 hours. After requesting a quote from Ridwan, we no longer needed to change our project design since the total 3D print times quoted for this project reduced to 5 hours which meets the total 3D print requirement limit. This quote also states that the 2-hour limit of 3D printing requirement per part is not exceeded.

 

Related requirements:

Level 1 Requirements:

C-11:

For quick production of the prototype, the preliminary project shall be restricted to six hours of total printing time with a two hour limit for each single print.

Level 2 Requirements

L2-5:

The robot shall use 3D printed chassis and legs. This follows from the project level requirement about using 3D printed parts.

L2-5a:

The robot shall use PLA or ABS filament in the fabrication of the chassis and legs. This will minimize the mass of the robot, while at the same time being strong enough to hold its weight.

 

Fig.1: 3D print time estimate based on Long Beach Makers Society’s quote

 

Fig.2: 3D print time estimate based on Ridwan’s quote

 

Conclusion

To further get ahead on this project, we went ahead and used the 3D printing services from the Long Beach Makers Society for our prototype due to Ridwan taking longer to respond with the 3D print quote. We plan on using Ridwan’s 3D printing services for our final project print.

 

References

  1. https://docs.google.com/document/d/1GCPoru2ZqR_VMB8tJ2FTlfe8vI3Ci1x_8kVdWjqsFGM/edit?usp=sharing

Alumni Night – 2018

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More than 100 CSULB College of Engineering alumni and their families turned out Saturday to check out student research projects, eat tacos, and watch the Men’s Basketball team beat UC Riverside. Northrop Grumman, Southern California Gas Co., Boeing, Southern California Edison, SpaceX, Qualcomm, and other top local employers were represented. Members from past projects were […]

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