Spring 2017 Velociraptor: Fritzing Diagram

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Table of Contents

Authors

By: Mohammar Mairena (Electronics & Control Engineer)
Approved By: Jesus Enriquez (Project Manager)

Introduction

Before one can create a custom printed circuit board (PCB), one has to create a Fritzing diagram. A Fritzing diagram is a virtual electronic circuit that is modeled after a circuit tested on the breadboard. Fritzing is used to provide the layout of the breadboard given the tools needed for a future PCB design.

Fritzing Diagram

The diagram shown is the Fritzing diagram our group used for the Preliminary Design Review (PDR). The diagram is a very rough idea of the parts we are using for the final schematic. This diagram is meant to provide a general idea of the parts needed for the final PCB design. Each part shown serves a purpose.

The breadboard consists of the 3Dot board, three servo motors, two DC motors, an external battery, an A/D converter with rotary/shaft encoders, an additional low-dropout voltage regulator for the extra servo motor and a GPIO expander. Two DC motors are used to control the legs of the raptor, one servo motor to control the head and another to control the tail. The extra servo motor will be used to control the turning motion of the Velociraptor. Since the 3Dot board is only capable of utilizing two servo motors and two DC motors, a PWM expander is necessary for our additional servo motor. The PWM/Servo driver is not shown and should replace the GPIO expander in the design. The PWM/ Servo driver with i2C interface has the capacity to add extra servos through two pins, SDA & SCL (Data and Clock).

 

Note: The 3Dot board was taken from Fall 2016 Velociraptor’s fritzing diagram.

Resources

  1. http://web.csulb.edu/~hill/ee400d/Technical%20Training%20Series/07%20FritzingDocumentation.pdf        
  2. https://www.arxterra.com/fall-2016-velociraptor-w-fritzing-diagram/ 

Spring 2017 Velociraptor: RGB Color Sensor

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Table of Contents

Authors

By: Mohammar Mairena
Approved By: Jesus Enriquez

Introduction

The Velociraptor will compete in a game similar to Pacman. One of the requirements is that the Velociraptor shall attempt to collect as many red dots as possible while navigating the maze utilizing either a static or dynamic walk. As a result, we will be using an IR sensor to detect the dots in the maze. My choice for the color sensor is the Sparkfun RGB Color Sensor. The reason I chose this specific sensor (APDS-9960) is because of the detection range and the operating voltage at 3.3 volts. In comparison to other sensors, this one has a lengthy detection range of 4-8 inches.

Analysis

The SparkFun sensor includes examples of Arduino library code for color sensing and proximity detection. I tested the color sensor and proximity sensor with the library code. After hooking up the sensor to the breadboard and uploading the code, I placed different colors up to the sensor. I had a hard time distinguishing colors using the serial monitor on the Arduino interface.

Conclusion

In retrospect, the SparkFun RGB Color Sensor is an ideal infrared sensor for the Pacman game however, detecting the different colors (red, blue, green) proved to be very difficult. Another disadvantage of this sensor is that it is very miniscule and would only detect the red dots if they were large in size. Completing this experiment helped me realize how minute the sensor was and how important it is going to be to correctly place the sensor on the robot.

Resources

  1. https://www.sparkfun.com/products/12787

Spring 2017 Velociraptor: SolidWorks Hardware Design Model

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Table of Contents

Authors

By: Andrea Lamore (Manufacturing)
Approved By: Jesus Enriquez (Project Manager)

Introduction

Throughout the engineering design process, the SolidWorks model for the Velociraptor went through a series of changes as our team went through trial and error with the different components for the robot. This post includes some of the thinking that went behind the hardware design of the robot.

Hardware Design

Servo Holder

Previously we planned on 3D printing and ordering all the parts necessary to build out first prototype. I modified and added a few parts to the velociraptor skeleton in anticipation of some problems that might occur during the build phase.

Mounts for the server were added to the bottom of the velociraptor for hip movement. Two or one servos could be placed here to accomplish hip rotation.

Head & Tail

Horizontal ball bearing will be used to facilitate rotation of the head and tail and the hip. The weight of the velociraptor is being supported by the legs, meaning that the body will resting on the hip mechanism which is attach to the legs – bearing will be added along the shaft of the hip that attaches to the leg. In order for the horizontal bearings to turn properly the outer and the inner radius of the bearing must not both be resting on the same surface. Circular extrusions for the parts resting on the bearing will be used to allow for proper slipping. The same horizontal bearing mechanism will be used to facilitate head and tail rotation.

Leg Mechanism

An issue with the Theo Jansen mechanism is the inability to keep the foot parallel to the floor is. Instead the foot moves in parallel with the legs circular motion. This means that that the whole body will shift back and forward with the foot motion when the velociraptor takes steps. With our first prototype, where we intended to use servos, a mechanical mechanism to keep the foot parallel to the floor could easily be incorporated into our design. A rounded out sole and a pair of springs attached to a pivoting joint at the angle was incorporated into the design in order to keep the foot parallel while  it is carrying the weight of the velociraptor(when it is the supporting foot being used to stand). The rubber sole will give the velociraptor height in order to prevent the toe from hitting the floor on steps and to keep the foot from slipping.

 

 

 

 

 

 

 

 

Conclusion

After going through the design process, there was still consistent changes throughout the semester in terms of Hardware design as our team consistently went through prototyping. As a result, we ended up deciding to do most of the manufacturing through laser cutting instead of 3D printing according to our original plan.

Spring 2017 Velociraptor: Servo Torque Test

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Table of Contents

Authors

By: Mohammar Mairena, Electronics & Control Engineer

Approved by: Jesus Enriquez, Project Manager

Introduction

The torque needed to move the different parts of the robot are specified by the Design and Manufacturing engineer. By testing the torque required at a specific location of the robot, one can prove the servo chosen will handle the stress placed at a certain location.

Analysis

Based on the measurements given by the Design and Manufacturing engineer, the servo placed at each hip will need to support 400 g at a horizontal position.

The experiment was done using a water bottle, HXT900 Micro Servo provided by Professor Hill, and a piece of string attached to the water bottle. The water bottle weighed approximately 408 grams, mimicking the weight that the servo (at the hip) will handle. The servo must rotate completely, without a stall under the 408 g load. The torque requirement at the hip was successful and rotated without a stall. Power came from the 3.3 V pin on the Arduino Uno and the current reading at 3.3 V came from the digital multimeter from the lab. At 3.3 V and under a 408 gram load, the HXT900 Micro Servo drew 180 mA of current.

Since the shaft radius of the servo is 2 mm and the weight of the water bottle is 408 grams, we can multiply them to get the Torque required at the hip. 2 mm converts to .2 cm, 408 g converts to .408 kg. Together, the torque required is .0816 kg*cm, which is equal to 1.13 oz-in.  

 

HXT900 Servo Placement Voltage Current Drawn Weight Torque Needed Shaft Radius
Hip 3.3 V 180 mA 408 g 1.13 oz-in 2 mm

 

 

Conclusion

It is important to note that at each hip, the servo will need to provide 1.13 oz-in of torque. As a result, the current drawn at each hip will be around 180 mA. Since the servos at the hips will only be used to make turns, the current drawn does not place much stress on the 3Dot battery. Max current output is 500 mA for the 3Dot Battery. The servos will not exceed the 500 mA limit.

Resources

  1. https://hobbyking.com/en_us/hxt900-micro-servo-1-6kg-0-12sec-9g.html
  2. http://www.rcuniverse.com/forum/giant-scale-aircraft-3d-aerobatic-110/2197950-how-do-you-test-servos-torque.html

Spring 2017 Velociraptor: Range of Motion Prototype

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By: Andrea Lamore (Manufacturing)
Approved By: Jesus Enriquez (Project Manager)

Table of Contents

Introduction

The range of motion of the leg determines the type of step the robot will take. A static walk requires a different stride from a dynamic walk and it is important to pick the linkages in the leg according to the type of walk that the robot will be using. The robot is to fulfill the following requirement:

L1-7: The Velociraptor shall be able to perform a static walk

 

Prototype

The velociraptor we are building shall have a static walk which uses two DC motors, so the Theo Jansen linkage was chosen as the optimal leg design for the robot. The following is the 3D printed model of the Theo Jansen Linkage. Before choosing the Theo Jansen Linkage [1] a series of other leg designs were cutout from cardboard and pinned together at the joints to simulate range of motion on a 2D plane.

Figure 1: Theo-Jansen Leg Mechanism Prototype

Conclusion

The 3D printed model of the Theo Jansen Linkage was scaled up for this prototype just to get an early idea of whether or not to implement this idea into our design. This leg mechanism will be rotating upon a single axis of rotation using a DC motor to over all drive the load of the robot.

References

[1]: https://en.wikipedia.org/wiki/Jansen%27s_linkage

Spring 2017 Velociraptor Preliminary Project Plan

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Project Team:
Jesus Enriquez (Project Manager)
Oscar Ramirez (Mission, Systems, & Test)
Mohammar Mairena (Electronics & Control)
Andrea Lamore (Manufacturing)

Table of Contents

Work Breakdown Structure

By Jesus Enriquez (Project Manager)

The figure below shows the Work Breakdown Structure for the Velociraptor project splitting the responsibilities and tasks of each member within their respective division. The structure was developed through research and development of Level 1 Requirements that were agreed upon between the Customer and Project Management team. Specific tasks were assigned as solutions to complete the mission profile of the project as explained in the Preliminary Design Document.

Project Schedule

By Jesus Enriquez (Project Manager)

The following figure below show the project timeline from a Top Level Project and System/Subsystem Level perspective. The tasks within the Top Level Perspective derive from the Level 1 requirements as agreed upon between the Customer and the Project Management team. The top level consists of 4 main components: Planning, Design, Assembly, Project Launch. These different components have specific tasks that are critical paths to one another throughout the semester in order to reach project completion.

The system/subsystem level project schedule is structured to compliment the Product Breakdown Structure and the tasks assigned to each respective division. These tasks are split amongst the systems and subsystems engineers as shown in the figure which include MST, E&C, and Manufacturing.

Top Level Schedule

System/Subsystem Level Tasks

Burn Down & Project Percent Completion

The figure below shows the burn down report graphically representing metrics of the project and how well our project team is meeting project deadlines. Our project was graphed in percentage terms over the course of 15 weeks (full semester). As detailed in the figure, the “Orange” data shows us the actual work or state of the project completed, whereas the “blue” data shows us the ideal task completion our project should follow. This Burn Down report follows the task as given in the Gant Chart shown in the Project Schedule.

 

System Resource Reports

By Oscar Ramirez (Mission, Systems, & Test)

Mass Report

The goal for the mass of the velociraptor was to be able to carry a sufficient load (secret weapon) while continuing to operate normally. The mass of the robot should not affect basic functions such as walking or turning. The mass ideally should be less than one kilogram since power consumption from our motors will begin to become an issue. The total expected weight of the robot is 850 grams and falls below one kilogram, which should be sufficient enough for our motors to handle. The aluminum frame while sturdy is a lightweight metal with a low density and weighs less than polylactic acid (3d printed plastic).

Power Report

The amount of power that will be consumed by the velociraptor will ideally less than 5500mA. For this we will need four batteries that can provide this much or greater combined current. The majority of the power being consumed is from the Servo and DC motors but the 3DoT board and the custom PCB will also have an expected current draw of 750mA. The rest of the current drawn from the robot is almost negligible compared to the motors and boards but is still accounted for. Finding the type of batteries that can supply this much combined current should not be too much of an issue since most batteries that can power our robot typically output more than 1500mAh.

 

Project Cost Estimates

By Oscar Ramirez (Mission, Systems, & Test)

Cost Report

The overall cost of the project should be $266.54 therefore a budget of $300 should cover all expenses and uncertainties. The highest factors contributing to this cost are the motors and custom PCB, which should take a considerable amount from the budget since they are the main components. There is some uncertainty with the custom PCB cost since we have gotten some rough quotes from different suppliers. The material should be relatively cheap since we are using aluminum but the cost to stencil the aluminum to our design is a cost that has been accounted for in the miscellaneous section of the cost report. More miscellaneous costs include wire, small components, and additional parts. Overall this project could be completed with a budget of $300 but this is not accounting for the 3DoT board.

Resources:

  1. https://hobbyking.com/en_us/towerpro-mg92b- 360-mini- digital-robotic- servo-3- 5kg-0-048sec- 13-8g.html
  2. http://arxterra.com/fall-2016- velociraptor-w- preliminary-project- plan/
  3. https://www.adafruit.com/products/2019gclid=CjwKEAiA3NTFBRDKheuO6IG43VQSJAA74F77G0GPI6v5JDgxwulfMspg8EP1gATbZGylBD57y4JpBoCU9Pw_wcB
  4. https://www.metalsdepot.com/products/alum2.phtml?page=sheet
  5. http://cds.linear.com/docs/en/datasheet/1107fa.pdf
  6. https://www.arxterra.com/spring-2016- velociraptor-preliminary- project-plan/

 

Spring 2017 Velociraptor Preliminary Design Documentation

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Velociraptor Team:

Jesus Enriquez (Project Manager)
Oscar Ramirez (Mission, Systems, & Test)
Mohammar Mairena (Electronics & Control)
Andrea Lamore (Manufacturing)

Table of Contents

Program Objective/Mission Profile

By Jesus Enriquez (Project Manager)

The Velociraptor Biped, inspired by that of the Titrus-III model developed by the Tokyo Institute of Technology, is to meet customer expectation through demonstration in a negotiated battle defined between the customer and the Robot Company project teams. While carrying out the mission, the Velociraptor will be operated through video support from a remote location using an assigned support vehicle from The Robot Company. The Velociraptor will be further controlled by a designated user through the Arxterra mobile application.

References:
EE 400D S’17 Project Objectives and Mission Profiles

Requirements and Verification

Program/Project: Level 1 Requirements

By Jesus Enriquez (Project Manager)

  1. The velociraptor budget shall not exceed an estimated cost based on an agreement between the customer and the project team
  2. The Velociraptor Biped Robot shall demonstrate that it has met the capabilities expected from the customer during the EE 400D Final on May 15th, 2017
  3. The Velociraptor should resemble a Velociraptor of the Theropodous Dinosaur Suborder
  4. The Velociraptor will use a 3DoT board embedded system
  5. The Velociraptor will use the Arxterra Android or iPhone Application and/or control panel to control the Velociraptor
  6. The Velociraptor shall operate with an external power source for a minimum time based on an agreement between the customer and project team regarding the mission objective
  7. The velociraptor shall use an external PCB with an I2C interface as the 3DoT board
  8. The Velociraptor shall use a 3DoT board while using I2C to communicate with electronic sensors, A/D converters, and GPIO
  9. The Velociraptor with its support vehicle shall have no more than one top secret weapon, approved by the management team

References:
Fall 2016 Velociraptor (Th): Preliminary Design Document
Spring 2016 Velociraptor: Preliminary Design Document

System/Subsystem: Level 2 Requirements

Mission, Systems, & Test

By Oscar Ramirez (MST)

  1. The Velociraptor Biped Robot shall use a 3DoT board as a servo motor driver and main microcontroller unit on the Biped
  2. The 3DoT board shall also work alongside the main PCB board and other on board sensors, drivers, and the Bluetooth communication system
  3. The Bluetooth communication system on the Velociraptor Biped shall be used to sync the user’s Android/iPhone device
  4. The user shall communicate with the Velociraptor Biped Robot via the Arxterra Android/ iPhone application to perform all the required tasks
  5. The power source shall be able to fit inside or on the robot and must be integrated into the Velociraptor Biped such that it does not affect the functionality of the robot
  6. The Velociraptor Biped’s 3DoT board shall use the appropriate libraries to communicate with the accelerometer, A/D converter, servo motors, and all other components on the PCB
  7. The Velociraptor Biped testing shall be conducted twenty-five feet from the robot and via a live feed to simulate the challenge conditions that are TBD

Electronics & Control

By Mohammar Mairena (E&C)

  1. The external battery should last for up to one hour
  2. The robot shall equip the right amount of torque to bear the weight of the Velociraptor
  3. The Velociraptor will use one DC motor for each leg
  4. The Velociraptor should use rotary encoders/sensors
  5. The Velociraptor will use one servo motor for the head and one servo motor for the tail to work independently of each other

Manufacturing

By Andrea Lamore (Manufacturing)

  1. The structure of the Velociraptor shall be made of Aluminum and/or 3D printed material
  2. The feet of the Velociraptor will be padded with rubber soles
  3. There will be a total of TBD motors within the body of the Velociraptor
  4. The Velociraptor shall be capable of calculating its center of gravity dependent on the position of its motors allowing it to adjust itself
  5. The Velociraptor will use servos and motors capable of supporting the body with the legs
  6. The Velociraptor shall be capable of achieving a static walk

References:
https://www.arxterra.com/fall-2016-velociraptor-preliminary-design-documentation/ https://www.arxterra.com/3dot
https://www.arxterra.com/fall-2016-velociraptor-th-preliminary-design document/#Electronics_Subsystem_Requirements

Design Innovation

By Jesus Enriquez (Project Manager)

After researching through the different designs of the previous generations of Velociraptor Biped Robots, it was noted that the certain types of leg mechanisms such as the Theo Jansen linkage was not appropriate to get the Robot to walk in a dynamic fashion but rather a static motion since it can only move forward and backwards rotating along a single axis. This limits the robot in terms of flexibility to move and turn in a dynamic fashion. Considering the mission of this robot per the customer’s request, it is essential that the robot have flexibility in its ability to move and turn under certain conditions. Using the creative process, our group was able to generate a few solutions.

Creativity Presentation

System/Subsystem Design

Product Breakdown Structure

By Oscar Ramirez (MST)

Power

The Velociraptor Biped will be powered by a portable power source that while not taking away any functionality or balance to the Biped must also be able to power the robot.

Body

The frame of the robot must have a strong material considering it will have a higher center mass when walking dynamically. The frame will consist of the head, tail, legs, and chassis. Aluminum will be ideal for this since it is not only a strong but lightweight material. Aside from the physical advantages to using aluminum the cost will also benefit the design since aluminum is going for about $30 per 4 square feet at 1.6mm thickness. This translates to a little more than one and a half kilograms of aluminum but not all of the 4 square feet sheet will be used and the frame of the robot will likely be the bulk of the mass.

Sensors and Drivers

An accelerometer will be used to help while walking to track motion and ensure that the system is not off balance. An analog to digital converter will also be used with the DC motors to track the position of the motors rotation and translate it into digital data that will be read into our microcontroller. Drivers will also be used for the DC motors since the microcontroller cannot directly control the speed of the motors.

Motors

As required by the customer, DC motor will be incorporated into our design. There will be two total DC motors that will provide motion to our Velociraptors legs and carry the majority of this load. Servo motors were used in the past but DC motors are better suited for the task since the can handle more torque. Servo motors will still be used in our design but they will be restricted to controlling the head and tail to move in sync with the center mass of the robot. Stepper motors will also be used to help provide more stability and needed torque for the legs.

PCB

There will be two PCB boards incorporated in our design. One of them will be our 3DoT board that will contain our microcontroller and control the servo motors and the other will be the main PCB board that will have all other sensors, communications systems, and drivers.

Software and Communication

The Velociraptors software will be based in C++ and written in an Arduino sketch. This sketch will control all motor functions and communicate to the Bluetooth module. The Bluetooth module will then sync with the users Android or iOS device and be controlled via the Arxterra control panel application. This application will have a GUI that will let the user perform any function of the robot such as walking, turning, and use of the on board secret weapon.

References:
http://arxterra.com/fall-2016-velociraptor-preliminary-design-documentation/
https://www.metalsdepot.com/products/alum2.phtml?page=sheet
https://www.arduino.cc/
https://www.arduino.cc/en/Main/ArduinoMotorShieldR3

Electronic System Design

System Block Diagram

By Mohammar Mairena (Electronics & Control)

Shown above is the block diagram for the electronic design. Within the 3DoT board is the I2C interface that allows the user to add multiple devices using the SDA and SCL pins (data and clock, respectively). The block diagram highlights the importance of the micro-controller as the root of each and every device as well as the significance of the micro-controller in terms of communicating with certain devices.

Interface Definitions

By Jesus Enriquez (Project Manager)

 

Reference:
https://www.arduino.cc/en/Hacking/PinMapping32u4

Mechanical Design

By Andrea Lamore (Manufacturing)

The velociraptor design be broken down in the following: The legs, feet, and the head-tail.

The entire design is going to be top-heavy and tall. Making the device top heavy will allow for good traction to floor and a small moment of inertia at the body so the top (the body) is more stable than the legs. The tall height in the legs makes it so there is a longer radius between the body and the feet, this also increases the moment of inertia at the body. A longer radius will give the robot more time to catch itself.

Leg Structure
The leg’s structure is going resemble that of a robot’s that is able to complete a passive dynamic walk. Without a mechanical control for preventing “bounce back” in the knee (referring to the knee bouncing back to bent after straightening), the leg design will not be able to complete a passive dynamic walk. Instead of a mechanical mechanism to prevent bounce back, there will be two motors used to control each leg – like the Titrus III design. One motor is responsible for the knee motion and the other for the swing of the hip. Using a combination of the successful passive walking robot and the Titrus III model, we will be able to create a leg that has the physical structure required for both passive and dynamic walking.

Static Walk
For the static walk the legs will be crouched by bending the knee and rotating the hip. This crouch will lower the center of mass and make the robot’s stance more stable. In the crouched position, the robot will utilize its head and tail to shift the center of mass from side to side depending on the foot that is stepping. In the crouched position the knees will move forward and the robots center of mass will be shifted, the upward motion of the head will be used to compensate for that forward motion. The tail will be capable of being used as a third leg so that the robot may utilize a very stable tripod stance. 

 

Turning
Turning will be controlled by motor as the hips. The motors responsible for turning will be placed here in order to keep the top heavy and reduce bulk in the legs so that the legs may accelerate as fast as possible and thus catch the robot as it falls on each step faster. The hips, if viewed from the top will angle the leg away or towards being in parallel with the other leg.

Feet
The feet will be statically joined at the ankle in order to reduce the amount of motors needed. If the legs need not enter the crouching position then the static flat foot with the heal attached to the ankle would suffice, however, since the robot will be crouching, the foot will need to roll over onto a different plane in order to keep the robot stable. To solve the problem, the robot will be able to bend its leg backwards (in the opposite direction of the dynamic walk bend) and roll over onto the ankle plane which will be at a slightly different angle from the rest of the lower leg.

Head/Tail
The head and the tail will move up & down and side to side. This mechanism will be that of the Titrus III robot, which used a “horse reign” schematic to control the head and tail. This “horse reign” method is similar to the reign of a horse in that two motors control the head/tail to move wither side to side or up and down. When one of the motor is rotated the head will turn either away or toward the motor in motion by moving left to right. If both motors are rotated in the same direction the head/tail will either lift or fall to the ground.

References:
https://www.youtube.com/watch?v=rhu2xNIpgDE&list=LLNnlTvhtytEM7T9W2Ou5IGA&index=27
https://www.youtube.com/watch?v=GxVv4WNlXMA&index=29&list=LLNnlTvhtytEM7T9W2Ou5IGA

Design & Unique Task Descriptions

Electronics & Control

By Mohammar Mairena (E&C)

The battery used to power the Velociraptor must take into account a few things such as: current capacity and mass of the battery with relation to the robot’s total weight. In order to choose the right battery in accordance to its specifications, tests must be run. The Servo motor will be under different load conditions and we will record measurements for current drawn in each unique load condition. Additionally, the operating voltage for DC and Servo motors will be 5V.

Velociraptor Electronics & Control Tasks

  • Perform a servo test to determine the servo load vs the current drawn with respect to the load
  • Conduct trade off study to determine which DC motor best serves 3DoT board
  • Conduct trade off study to determine which Servo motor best serves 3DoT board
  • Create a fritzing diagram to test the breadboard
  • Create an electrical schematic/PCB based on Eagle CAD
  • Determine the total current drawn in order to pick the correct battery for the robot
  • Conduct control algorithm tests for Servo motors through Arduino IDE
  • Conduct control algorithm tests for DC motors through Arduino IDE