By: Alexander Clavel (Project Manager)

Approved by: Alexander Clavel (Project Manager)

Introduction

The BiPed projects goal is to be able to create a walking bipedal robot that is able to perform static walking. The definition of static walking is walking that remains constantly balanced throughout the robots entire walk. In theory, when the power to the robot is cut off, the BiPed should stay standing and balanced. This is one of our main requirements. This blog post shows the process of building one of the prototypes.

Design/Construction

The overall construction which included buying all the parts and materials and then assembling them together took a little less than a day. We decided to go with a design that was found through reserach on youtube of walking bipeds. We were looking to find something simplistic as to be able to stay light on the material as well as the power draw on the electrical components. The BiPed we based this prototype off can be found here in a video. In the video, the biped uses a straight leg with no linkage and uses circular motion to walk forward. It is also a very small design that reaches a little under 20 centimeters in height which is something we would like to incorporate in ours.

Gear Box

Figure 1

Figure 2

This was the first attempt at using a gear/pulley combination to drive the robot. The white round gears on the outside of the wood area in figure 1 show the rotational movement that the legs would be taking during the walking motion and the actual legs would be connected to the metal pegs sticking out. The rubberband in the pulley in figure 1 would wrap up to the pulley that is attached to the motor in figure 2. I tried using a 1 to 1 ratio for the pulley on the shaft to the pulley that will drive the 2 gears next to it. From reasearch done and experience with cars, I learned that using a smaller radius for the driver to a larger radius produces more torque, but less speed. For our requirements we will be needing that torque to be able to drive the robot, but we will also need to keep it fast enough to pass our speed requirement. From this reasoning I tried a 2 to 1 or 3 to 1 for the purpose of testing the walking motion. The two additional bevel gears in figure 2 were to work towards a solution for the balancing problem, but it was never completely finished due the professor not liking the design of our feet (which overlapped each other) so the design was to be changed anyways.

Leg Design/Movement

Figure 3

As stated before, there is a single wooden board for the legs that use a rotational motion for the legs. Figure 3 shows a side view of the gear box where the legs would be attached. The bottom of the robot is to the right of the image. This being just a test, I placed the pegs very close to the shaft because I just wanted to at least see if it would rotate. The final product would have to have a larger radius from peg to shaft so that the robot will be able to get a decent distance with each step. Again our design was kicked back because the feet  that were attached were overlapping to account for the balancing. Without the overlapping feet, the balancing mechanism at the top of the robot would have had to be completed.

Conclusion

Figure 4

Figure 4 shows the entire main body of the biped attached. Again the rubberband is connected from the pulley in the gearbox to the pulley driver connected to the motor. The legs were not added to the image, but again, they are connected to the metal pegs sticking out on the sides. To restate it, the gear at the top of the robot is vestigal at this point and doesn’t serve a purpose for this prototype but should play a bigger part in the final product. When completely assembled, the robot shows that it does indeed give a clean walking motion while being held in the air. When placed on the ground the robot does “walk”, but it was a very rough, sloppy, and unbalanced motion. As it moves forward it does wobble side to side to a large degree, but at a very slow pace. Concluding comments would be that:

• It does perform a walking motion
• It does not stay balanced without the overlapping feet unless a balancing mechanism can be created
• The walking speed is very slow.

There will need to be more adjustments to the prototype for application on the final product.

Referrences

1. http://www.blocklayer.com/pulley-belteng.aspx
2. http://tech.txdi.org/gearsandpulleys
3. https://www.youtube.com/watch?v=Z7N0xCDVzIA&feature=youtu.be

By: Abraham Falcon (Electronics and Control)

Approved by: Alexander Clavel (Project Manager)

Introduction:

Electronics and Control engineer is to create a custom PCB and to layout the components to be used. The PCB components are a PCA9685 PWM expander, pin headers for the LEDs and a pin header for the color sensor.

Eagle Cad Schematic:

The Biped PCB schematic below shows what the main components are to be use with the 3Dot board, which is the color sensor and a LED counter.

This PCB schematic is the third version and to be used on the Biped mainly for the game. Previous PCB schematics had two extra servos from the main design of the biped. As we moved forward with the design of the Biped, the customer stated that the power was the be supplied without an external battery. Power should soley be provided by the 3Dot board battery. The servos were eliminated to reduce the power consumption and therefore the PCB schematic above is the final version to be used with the 3Dot Board.

The PCB needs to communicate with the 3Dot board and the PCA9685 PWM expander will handle this. The PCA9685 PWM expander handles multiple PWM pins as the 3Dot board does not provide. Connecting multiple devices to the PCA9685 PWM expander will communicate to the 3Dot board through the I2C bus.

There will be two LEDs for the Biped to represent the eyes that are colored red and signify that the robot is indeed on. The other LED which is green is to represent a counter for collecting colored dots from the “end of semester” Pacman Game. All the LEDs connect with a 1k Ω to PWM expander, which these resistors are to limit the amount of current going through the PWM expander for protection. The LEDs are not physically connected to PCB board therefore it will use pin headers so the LEDs can freely be placed anywhere around the Biped.

For the Biped to sense the color dots from the game it will be using a Adafruit RGB Color Sensor and this sensor will also not be physically connected. The colored dots are placed on the floor therefore the color sensor must be placed on the foot to sense the color dots. The pin headers have the connection needed to connect to the 3Dot board and be powered by it. The pin headers connect to the I2C bus from the 3Dot board, which are SDA and SCL. Also from the 3dot board the power and ground can be connected to the sensor provide from 3Dot board connection. The pin headers are placed so that the color sensor can freely be placed anywhere on the biped and for this design we chose it to be on the foot.

The other components on the PCB schematic were provide from the product website, where they also provided Eagle Cad files. All the components are surface-mount devices. These components were left alone as the product works with it.

Conclusion:

The completed PCB schematic is simple but pushed our design to have less power consumption and to participate in the “end of semester” Pacman Game. The completed PCB Schematic is sent to the manufacturing engineer to layout the PCB and to be completely assembled.

Referrences:

1. http://www.mouser.com/ProductDetail/NXP- Semiconductors/PCA9685PW118/?qs=sGAEpiMZZMvKM5ialpXrmnWDpPMxsdrM

2. http://www.mouser.com/ProductDetail/Broadcom-Avago/HLMP-3301/?qs=sGAEpiMZZMsx4%2fFVpd5sGeS9q14uN1KF

3. http://www.mouser.com/ProductDetail/Broadcom-Avago/HLMP-3507/?qs=sGAEpiMZZMsx4%2fFVpd5sGbU8v9L8Znih

4. https://www.adafruit.com/products/1334

Alexander Clavel – Project Manager

Jacob Cheney – Missions, Systems, and Tests

Abraham Falcon – Electronics and Control

Mikaela Hess – Manufacturing and Design

Phong Nguyen – Manufacturing and Design

Work Breakdown Structure (WBS):

By Alexander Clavel (Project Manager)

Figure 1: WBS

The Work Breakdown Structure shows the responsibilities and tasks of each member of the team. It breaks down the individual tasks and specifies exactly which division and or person it falls under. Figure 1 shows the breakdown for the BiPed Project. The structure was derived from working with the level 1 requirements previously established, the product breakdown structure, as well as the different design innovation methods we used. To set specific tasks, we had to look at what had to be done on the product as well as what we could do. These can all be referenced to the Spring 2017 Preliminary Design Document that was completed previously.

Project Schedule:

Top Level & System/Subsystem Schedule:

Figure 2

Figure 3

The project schedule gives a timeline overview of the work that needs to be done and it what time frame it needs to be completed in. Figure 2 depicts the top level schedule and the entire timeline of the BiPed project. The schedule is broken down into 4 phases which include planning, design, assembly, and project launch. The planning phase mainly consists of research required for the project as well as coming to a clear definition of the mission objectives. After the planning phase comes the designing of the BiPed. Considering that a BiPed has yet to be built using DC motors, this is proving to be a difficult part of our engineering process. Assembly comes next with project completion and project launch in conclusion.

In Figure 3 the schedule is broken down even further to specify tasks for each individual. These tasks can be traced back to the Work Breakdown Structure and include purchasing components to modeling and prototyping. Some of these jobs are ongoing throughout the project while some have specific deadlines that need to be met.

Burndown and Project Percent Completion:

Figure 4

Figure 4 is a representation of our progress by percent. The vertical axis is a measurement of the percentage of tasks that need to be completed while the horizontal axis is the number of weeks. The blue line is the ideal percentage of work that should be done while the orange line is the percentage of work that we have actually done so far. We fell behind in the beginning in terms of tasks that need to be done but we were able to make up about 30% of the work. Most of that work is still currently in progress and not yet complete.

System Resource Reports:

By Jacob Cheney (Missions, Systems, and Test)

The Mass Report shows the weight of each individual component of the system and the total of all of them combined. For some of our parts, we looked at previous semesters to get a better approximation of how much some of these components weigh. Others were found elsewhere on the web or measured by the manufacturing engineer. For the entire system, our initial calculations of the Total Expected weight came out to 392.95 grams. This lead to a Total margin of 145 grams and a Contingency of 152.05 grams.

The power resource report shows the division of current throughout the Biped system. Current estimates for each component are based on their respective datasheets. Our calculations for the total expected current came out to be 1150 mA. This left us with a total margin of 610 mA and a contingency of 660 mA.

Project Cost Estimate:

The Cost Report lists all of the parts and materials needed along with the purchase price for each. The Total Expected Cost for everything came out to $180.50 with a Total Margin of $54 and a contingency of $73.50.

The BiPed Team:

Alexander Clavel – Project Manager

Jacob Cheney – Missions, Systems, and Test

Abraham Falcon – Electronics and Control

Mikaela Hess – Manufacturing and Design

Phong Nguyen – Manufacturing and Design

Program Objectives/Mission Profile:

By Alexander Clavel (Project Manager)

The customer has asked for a 7th generation robot that will be able to walk with the use of DC motors in replacement of servos. Based on the request of the customer, the bipedal robot will participate in the “end of semester” game. During the game, the robot will do battle with the velociraptor while using video support that is provided by the spider bot and pathfinder rover. With live video feed, the biped will be controlled with the Arxterra phone application to complete its mission.

Spring 2017 Requirements:

Project: Level 1 Requirements

By Alexander Clavel (Project Manager)

1. The biped shall be able to achieve a static walk using dc motors.
2. The Biped should be able to turn.
3. The biped shall be able to participate in the “end of game” semester.

As stated by the customer

    4. The biped shall be controlled with the use of the Arxterra phone application.

As dictated by rules of the game

    5. The biped shall utilize a 3Dot board with custom SMD I2C shield.

As dictated by rules of the game

     6. The biped should be able to operate for an hour.

     7. The biped should be able to achieve dynamic walking.

     8. The biped shall fit within the classroom cabinets (size to be determined)

As instructed by the customer

     9. The biped shall be completed by the last day of class on Monday, May 15th, 2017.

As listed in the school schedule

MST: Level 2 System/Subsystem Requirements:

By Jacob Cheney (Mission, Systems, and Test)

1. The BiPed shall have a Bluetooth v 4 .0 BLE Transceiver integrated circuit that will be able to communicate with an Android or iPhone.
2. To maintain balance while static walking, the Biped shall use two servos as ankles to shift the center of gravity.
3. The 3Dot Board shall receive commands from the Arxterra app via Bluetooth Transceiver. It will then decode and transmit data to the DC motors and servos.

E&C: Level 2 System/Subsystem Requirements:

By Abraham Falcon (Electronics and Control)

Abraham Falcon (Electronics and Control)

1. The Biped will use two DC Motors for each hip for the walking movement.
2. The Biped will use two Servo Motors for each ankle for a legs side movement.
3. The Biped will use two Servo Motors for a turning movement.
4. The Battery’s duration will last up to an hour.
5. DC motor shall operate at 5 Volts for a static walk.
6. Servo Motor shall operate at 5 Volts for a static walk.

Source Material:

https://www.arxterra.com/3dot/

M&D: Level 2 System/Subsystem Requirements:

By Mikaela Hess (Manufacturing and Design)

1. The Biped will have a height restriction in order for it to fit in the closet with dimensions to be determined.
2. The Biped will have legs designed to hold up the weight of a 3 dot board, Arduino, servos and the DC Motors.
3. The Biped shall have an implemented design that makes the legs close together for better control of the center of gravity in order to achieve static walking.
4. The Biped shall optimize the constant speed of the Biped for an hour by designing a leg that optimizes each length of each step in order to play the end of the semester game.
5. The Biped should add an additional feature to the static design in order to achieve dynamic walking

Design Innovation:

Alexander Clavel ( Project Manager )

Through research of previous semesters requirements and final results, we developed our own areas of focus to create solutions for. Until now, most BiPed projects utilized servos to achieve walking, but ours will require the use of DC motors. As of yet, walking with DC motors has not been achieved so that has become our main area of focus. The Theo-Jansen approach gives us an initial approach to accomplish walking. Taking the “end of semester” game into consideration, the robot will also need to be balanced and be able to turn. Some ideas that were elicited from our creative exercises were to bring the legs closer in to allow for an easier shift in the center of gravity. Using the creative method, we devised different possible solutions for these problems.

Creativity Solution Slides

Systems/Subsystem Design:

By Jacob Cheney (Mission, Systems, and Test)

Product Breakdown Structure:

The product Breakdown Structure (PBS) is used to plan and display the outcomes of our project. The goal is to break down the product as much as possible to ensure nothing is overlooked. The hierarchical structure begins with the final product at the top followed by subcategorized elements below.

http://web.csulb.edu/~hill/ee400d/Lectures/Week%2004%20Modeling/e_Product%20Breakdown%20Structure.pdf

Good PBS Example (Velociraptor)

Electronic System Design:

System Block Diagram

The System Block Diagram shows the outputs for the ports of the DC motors, Servo motors, and the input for external power. The LDO 5V Regulator is used to increase the 3Dot board output voltage to the operating voltage for the Servo Motors. An Android or iPhone device with an Arxterra App will be used to control the Biped.

Source Material:

Fall 2016 Biped – Updated System/Software Block Diagrams  

Interface Definitions

Mechanical Design

By Mikaela Hess (Manufacturing and Design)

Pictured above is the initial idea that the Manufacturing engineers have designed. As can be seen above, we have the DC motors moving in the center of the body of the biped in order to have better control of the center of gravity. To make this happen, we must create a distance between the two DC motors large enough so that the two servos sized feet can be picked up and land onto the ground without disturbances. To go without the disturbances, we must create a distance of one servo between the DC motors, and an additional ⅕ of an inch of room to adjust for human error. Next, we placed the body on top of the DC motors, facing the other way in order to counteract the weight of the DC motors on either side, for better stability. This idea of having a long body was actually created from the Creative Project, where we forced a truck onto our biped design. The overall size of this Biped is to be under 10 inches. The body of the Biped is expected to be no more than 3 inches and the servo on the feet are expected to be no higher than 1 inch. With those calculations and the 1-inch radius in which the leg is designed to move around, the actual leg is to be designed in a total of 4-5 inches.

The actual walking of the biped is broken down into 5 steps here. In order to follow this design, the pictures are color coded according to the design’s components. In blue we have the representation of the circular path created by the DC motor and the pink segment. The pink segment is a sturdy piece of material that is directly linked to the DC motor and has a loose joint connection to the leg of the Biped, or the yellow piece in the picture above. Both legs start off in position one where the legs are bent and at rest at x and y equal zero on a radian circular graph. One leg then shifts its weight over by moving the leg over at an angle theta from resting position to the side by a servo. Once that is done, the DC motor then turns on and moves the pink segment to the negative pi over two positions on the same radial circular graph. This makes the body shift upward and lifts the other leg along with the body. After the segment goes to negative pi over two, it will move to pi on the radian graph, the ankle with resume its original position, causing the biped to take a step and then the legs will be programmed to reach equilibrium and resume its original position. Once that happens, the other leg repeats the same process and vice versa. Overall, the Biped should walk.

Once this design was created, I sent more photos and information to a Michael Oran Tobin, a Control Systems Engineer for California with PE Certification #CS7494. Once I had explained the servo use and parameters of the total design, it was made clear that my design would fail. What I failed to notice was the joint at the knee and the segment (yellow and pink where they connect), was that because there was no control onto that joint that the body could give out. As well, my design required precision that only DC motors with rotary encoding. A recommendation was made to use either a memory wire that straightens when current is given and loosens when there is none, or to use a servo at the knee for better control. The servo at the knee was decided to be a better option due to the memory wire being in early production and may not be able to handle the weight of the servo and leg. After going over the entire design, Michael Tobin strongly recommended doing more research on how humans walk and to consider how humans move their feet towards the center of gravity line to walk and then moves outward for better balance. As well, he suggested using a second wheel for better control of the joints. These pictures and ideas are pictured below and were made by Michael Tobin.

Overall, the design needs to reconfigured. More servos and research need to be done in order to create a working and walking Biped. The difficulty in this task is that most designs for biped are made using solely servos or stepper motors, which means this Biped leg design has to be made from scratch, but with help from other engineers and more research, it should be made possible. Also, a discussion with the project team and customer should be set up in the near future to discuss the use of more servos or motors.

Mechanical Design (Continued)

By Phong Nguyen (Manufacturing and Design)

This picture shows us a biped design based on human structure (hip, knees, and feet). As shown above, we decided to design the Biped with two DC motors for each hip, two servo motors for each ankle, and two Servo Motors for a turning movement. The DC motors are responsible for lifting up the whole leg while the servo motors will be used to shift the center of gravity. If we want to turn left or turn right, the servo motor at ankle will be able to accomplish that like last semesters biped. Under the foot, we will use high friction material such as sandpaper, rubber, or plastic. 

http://robogames.net/symposium/2007/07-108-Vaidyanathan-AnnaUniv-AnalysisofBipedalWalkingRobot.pdf

http://embeddedprogrammer.blogspot.com/2012/08/simulation-of-humanoid-robot.html

Design and Unique Task Descriptions:

Electronics and Control

By Abraham Falcon (Electronics and Control)

Biped Electronics and Control Design Process/Analysis

According to 3Dot Board specifications, it only supports 5V Turbo Boost for driving DC motors and for the Servo Motors to be operated at 5V. Using a rated 12V DC Motor to be power at 5V to measure the current draw at no load conditions and stall current to know the maximum current the motor will use to determine the Biped Battery total current it can supply. Also, for a Servo Motor to be power at 5V to measure no load current and stall current to determine the maximum current it will draw to know what battery is needed.

Biped Electronics and Control Tasks

• Choose DC Motors to be compatible with the 3Dot Board’s TB6612FNG Dual Motor Driver.
• Choose Servo Motors to be compatible with the 3Dot Board’s Two 3.7v Micro and Ultra-Micro Servo ports using a Voltage Regulator.
• Perform Trade-Off Study on DC Motors to select for Biped for the 3Dot Board.
• Perform Trade-Off Study on Servo Motors to select for Biped for the 3Dot Board.
• Do Servo Motor Analysis to know what are the specs on a load condition on the Servo Motor and know how much mass it can handle at its maximum current.
• DC Motor Analysis to determine the maximum current under a load condition and know what is the maximum mass it can handle.
• Measure all currents of the motors to know the total current for the Biped Battery’s Specifications.
• Select a Power supply that will handle all the current that the motors are consuming.
• Create a Fritzing Diagram and test it on a breadboard to assure its properly working.
• Use Eagle CAD to create an electrical schematic (PCB).
• Using Arduino IDE to program the DC Motors and Servo Motors to work properly and to be successful.

Source Material:

Fall 2016 Biped – Updated Schematics  

http://arxterra.com/goliath-fall-2016-preliminary-design-documentation/

Manufacturing and Design

By Mikaela Hess (Manufacturing and Design)

Manufacturing Tasks

• Measure the cabinet’s height and reduce it by one inch and make that the height requirement (so there is room for error).
• Perform Trade-Off studies to see what implemented structures are used to make a robot walk using DC motors.
• Weigh out the servos and DC motors, 3 Dot Board, and Arduino to know the total weight capacity.
• Design a foot that has better grip and curvature for a smoother transition in steps.
• Perform a Trade-Off study to see what materials are the lightest and sturdiest material to handle the weight.