Spring 2018 3DoT Hexy: Product Breakdown Schedule

By: Raymundo Lopez-Santiago (Mission, System and Test)

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

Approved by: Miguel Garcia (Quality Assurance)

Introduction

This blog post covers the Product Breakdown Schedule (PBS) for 3DoT Hexy. This document follows the Work Breakdown Schedule (WBS) developed by Eduardo De La Cruz (Project Manager and Manufacturing Engineer). This PBS is split into five sections to outline the major components of 3DoT Hexy. The five sections are electronic hardware, software, movement, manufacturing, and power. Anything for movement which includes motors, joints, gears, and legs are the main parts in for mobility of the robot. Under the software section, communication via Bluetooth from a smartphone and the Arxterra app will allow for wireless control of 3DoT Hexy with custom commands. For electronic hardware, all peripheral sensors will be connected to a custom PCB.  Sensors used for this project include three UV light sensors which will aid in detecting intersections, an ultrasonic sensor which will aid in detecting other robots, and a gyroscope to aid in directional turning. For manufacturing, it includes designing a cam system. chassis, legs, joints and any other parts used for the mechanism. It also includes rendering models on Solidworks and 3D printing parts in either PLA/ABS plastic or other approved material. For the power section, 3DoT Hexy and its peripherals will be powered by a single 3.6V RCR123A battery. Power estimates of each components are further listed in the resource reports blog post.

Fig. 1: 3DoT Hexy Product Breakdown Structure

 

Conclusion

After going through two revisions after the PDR, I made sure this PBS was effective in following the WBS. For future reference, make sure to only define major components for the robot and not specific details. Do not try to go to a different path than the WBS, since the overall objective is to identify major components and who is responsible for them to further help with the production of the final product.

References

  1. https://www.arxterra.com/2016-spring-3dot-david-final-project-blog-post/
  2. https://docs.google.com/document/d/18vVkXfxwqulRn5qCdm2Y6NYleS1iGQ_p3y6FJUj5NJ4/edit

 

Spring 2018 3DoT Hexy: Interface Matrix

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

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

Approved by: Miguel Garcia (Quality Assurance)

Introduction

This blog post covers 3DoT Hexy’s final interface matrix. If interested in seeing our preliminary design interface matrix click here. The 3DoT Hexy interface matrix was developed with information obtained from datasheets for each device used and pins allocated from the 3DoT V 6.43a board. Based on our design, we needed to design two custom PCBs, one for all sensors and one with a boost converter to drive our motors as well as power three UV LEDs. To make things easy to understand, the interface matrix is broken up into three interface matrices. As seen in Fig. 1, the main interface matrix relates each custom PCB to the 3DoT board and how each PCB will connect to the 3DoT board. As seen in Fig. 2, the Custom Sensor PCB interface matric further breaks down in detail which sensors will connect to the PCB to make sure no pins are used more than once (except for power and ground). As seen in Fig. 3, the Custom Boost Converter PCB also breaks down in detail which peripherals will connect to the PCB to make sure no pins are used more than once (except for power and ground). After researching different UV sensors, we were unable to find ones that had different I2C addresses, therefore we needed to add an I2C expander to our circuit design. Based on availability and previous semester success, the model I2C expander model used is TCA9548A. The boost converter model used is TPS61253A.  The Light Sensor (UV Index Sensor) model used is Si1145. The gyroscope model used is ITG-3200. The Ultrasonic sensor model used is Parallax Ping (a HC-SR04 may also be used).

Related Requirements

Level 1 Requirements

L1-4:

The robot shall have a custom PCB as platform to build from and will incorporate peripherals for sensors

C-12:

The robot shall use a v6.43a 3DoT board.

Level 2 Requirements

L2-2:

The robot shall use a single RCR123A 3.7 V, 650mA rechargeable Li-ion battery to power the 3DoT board, which will power the drivetrain and all attached peripherals.

L2-3:

The robot shall use three Light sensors and three IR LEDs connected to a custom sensor PCB to handle intersection detection.

L2-4:

The robot shall use a Parallax Ping (or HC-SR04) ultrasonic sensor to handle robot avoidance.

L2-10:

The robot shall have (2) LEDs acting as eyes of the spider.

 

Update 04/24/18

Based on customer concerns with the TPS61253A 9-ball 1.2-mm x 1.3-mm WCSP package, we explored other methods to not use a boost converter and further investigate operating all electronics of the robot at the rated 3.7 V from the RCR123A battery. After improving the gear mechanism with the addition of bearings and bushings, we were able to operate the robot at 3.7V while having stable movement with weight attached on top of the robot (simulating the final weight of all devices used for the final robot configuration). Since this change occurred, we no longer will use any connections from J1 and J2 from the 3DoT board. UV LEDs will no longer be used and will be replaced with IR LEDs. Based on customer recommendation instead of using the 8-channel TCA9548A I2C model, we are going to use a 4-channel model: PCA9544A. All peripheral devices will be connected to the Custom Sensor PCB developed by Kris Osuna (Electronics and Control Engineer). The Custom Sensor PCB is connected to J3 of the 3DoT board.  Two additional extra LEDs are added to act as eyes of the spider.

 

Fig. 1: 3DoT Hexy Interface Matrix

Fig. 2: Custom Sensor PCB Interface Matrix

Fig. 3: Custom Boost Converter PCB Interface Matrix

Conclusion

This blog post covers 3DoT Hexy’s interface matrix. This matrix is composed of the available pins of the 3DoT V 6.43a board and how they connect to each custom PCB. When using the Custom Boost PCB conected to the 3DoT board, Make sure to remove JP7 on the 3DoT board. This will avoid you messing up the 3DoT board. The objective of this document is to allocate pins to components used in the design and make sure no pin is used twice (except power and ground).

References

  1. https://www.arxterra.com/2016-spring-3dot-david-final-project-blog-post/
  2. http://www.ti.com/lit/ds/symlink/tps61253a.pdf
  3. http://www.ti.com/lit/ds/symlink/pca9544a.pdf
  4. https://cdn-shop.adafruit.com/datasheets/Si1145-46-47.pdf
  5. https://www.sparkfun.com/datasheets/Sensors/Gyro/PS-ITG-3200-00-01.4.pdf
  6. https://cdn.sparkfun.com/datasheets/Sensors/Proximity/HCSR04.pdf

Spring 2018 3DoT Hexy: Booster Shield Layout

By: Kris Osuna (Electronics & Control Engineer)

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

Approved by: Miguel Garcia (Quality Assurance)

Introduction

3DoT Hexy needs to have a 5V source to power the micro metal gear motors and UV LEDs. We are using a booster to get 5V from a 3.7V battery source. Using the software Eagle CAD and the TI WEBENCH tool a schematic and PCB is being made. The original booster we purchased used a 9-ball grid array. This caused a lot of problems. Placing the chip on the PCB editor showed that it starts with clearance errors. This is due to the balls being so close to each other. With Professor Hill’s advice I approved all clearance errors and moved forward.

Requirements

  • Must have an output voltage of 5V and an output current of 1.1A

Materials

  • Eagle CAD software
  • TI WEBENCH interactive tool

Update 3 (April 19, 2018)

We will no longer be using a booster shield for a variety of reasons. 3DoT Hexy has been improved and can move with the load at 3.7V. We will no longer be using the UV LEDs at 5V instead we will be using IR LEDs at 3.3V.

Update 2 (April 13, 2018)

We changed the booster package to a SMD chip. The PCB board was made with no errors and awaits final approval.

Figure 1: Booster shield with the SMD chip produces no errors.

Update 1 (April 13, 2018)

The Eagle CAD DRC check kept producing errors. Placing polygons on the connecting balls resulted in error. Placing routes at different angles produced errors. Placing a route with the minimum width of 10 provided errors. We are looking at different solutions for this problem.

Figure 2: The TI WEBENCH interactive picture provided the schematic to use and even provided an Eagle CAD schematic file.

We were able to find the dimensions of a blank 3DoT board, as a reference for our PCB design:

Figure 3: Blank 3DoT Board 

Link to

  1. Blank 3DoT PCB

The current PCB still being worked on due to errors, nevertheless, we have provided a preliminary design of our schematic and PCB. The finished schematic and PCB will be uploaded when they are finished.


Figure 4: Booster Shield Schematic 

Figure 5: The dimensions of the blank 3DoT PCB shield were obtained and used for our PCB

 

Resources

  1. EAGLE Training

Spring 2018 3DoT Hexy: Sensor Shield Layout

By: Kris Osuna (Electronics & Control Engineer)

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

Approved by: Miguel Garcia (Quality Assurance)

 

Introduction

This blog contains the sensor shield PCB layout that will be sent out for fabrication. The PCB must contain these parts: I2C multiplex, connection to UV sensors, connection to LEDs connection to ground and power. The UV sensors, LEDs and booster are not going to be directly on the PCB. These items are going to be connected through wires so headers are going to be needed to connect them. Having so many headers provided a unique challenge. The headers take up a lot of space so they must be arranged carefully. I placed all similar headers together to reduce any confusion with silk layer text to clearly identify what sensors go where. It is important to know which sensor is at which header so that the software and hardware can communicate efficiently.

The very first initial draft had many minor issues that first time EAGLE CAD users will encounter. Power and ground routes should have a width of 16 and others have a width 10. I suggest using the polygon tool to create power and ground planes. I did not consider the size and price of the PCB. The first version was very large and very expensive. A helpful tutorial can be found under the resources. I highly suggest working on the schematic and PCB as soon as possible. The PCB will go through many revision before getting a final approval. It is very time consuming and then fabrication takes even longer.

Related Requirements

Level 1 Requirements

  • The robot will need to navigate remotely through a custom-built maze (built by AoSa image), memorize the path it took, start over, and autonomously travel through the path it took.
  • The robot shall avoid collisions if it encounters other robots while navigating through the maze. This involves detecting the robot, retracing steps back, and moving to a room that allows the other robot to have a safe passage.
  • The robot shall use a v6.43 3DoT board.
  • The robot shall demonstrate the capabilities of the 3DoT micro-controller for DIY hobbyists.

Level 2 Requirements

  • The robot shall use a single RCR123A 3.7 V, 650mA rechargeable Li-ion battery to power the 3DoT board, which will power the drivetrain and all attached peripherals.
  • The robot shall use 2 UV sensors connected to a custom PCB.
  • The robot shall use a HC-SR04 ultrasonic sensor to handle robot avoidance.
  • Ultrasonic sensor shall have a range of 0.5-meter radius to detect and respond accordingly to other robots.

Materials

  • Eagle CAD software

Version 4 (April 19, 2018)

Final Sensor Shield Version

Fabian sent me the PCB design back with minor changes and permission to send to fabrication. PCB was sent to Oshpark for fabrication with ‘Super Swift Fab’ option for quicker service. ‘Super Swift Fab’ was chosen because we are running out of time, which is why I suggest starting this process as early as possible.

Figure 1: The final PCB design 

Figure 2: Left: Front of our fabricated PCB, and Right : Back side of our fabricated PCB 

 

Parts:

  • 4-Channel I2C
  • Gyroscope
  • 8-pin header
  • Five 4-pin headers
  • 6-pin header

PCB now contains these parts: 4-channel I2C, gyroscope, connection to UV sensors, an 8-pin header, five 4-pin headers and a 6-pin header. The 8-pin header will connect to the 3DoT board, which will provide power, ground and four digital pins. Three of the 4-pin headers will connect to the UV sensors. A 4-pin header will connect the ultrasonic. The last 4-pin header will connect two controllable LEDs. The 6-pin header will connect to 3 LEDs. All headers are now labeled to reduce confusion. Waiting for approval from Fabian to send to fabrication.

Figure 3: Sensor shield version 3 

Version 2 (April 09, 2018)

Parts:

  • 4-Channel I2C
  • Gyroscope
  • 8-pin header
  • Five 4-pin headers
  • 6-pin header

A gyroscope was added to the design for turns. 5V power was taken out and all power will now come from the 3DoT battery. The 16-Channel I2C is now a 4-Channel I2C to save space and connections. Power and ground planes were added for convenience. The additions of planes reduced a lot of routes and cleaned the design.

Figure 4: Sensor shield version 2 

Version 1 (March 22, 2018)

The current PCB is still being worked on. The current schematic image (link 1) and PCB image (link 2) can be found under the links section. The finished schematic and PCB will be upload when they are finished.

Parts: 

  • 16-Channel I2C
  • 8-pin header
  • Six 4-pin headers
  • 2-pin header
  • 6-pin header

Figure 5: Circuit Schematic 

Figure 6: PCB Layout 

Resources

  1. EAGLE Training

 

Spring 2018 3DoT Hexy: 3D Model (Preliminary/Revisions/Final)

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

Approved by: Miguel Garcia (Quality Assurance)

Introduction

This blog post contains detailed explanations for the 3D components generated in Solidworks. This post does not contain any dimensions on how to make them in solidworks. If interested in the dimensions of specific parts please see “Spring 2018 3DoT Hexy: Mechanical Drawings” . Our first iteration which is also our preliminary design will be labeled as Update 1: 3DoT Hexy Mk-1 (Prototype).  Revisions will be made within this blog post, and will appear under the table of content as “Update n” followed by the date updated. 

Related Requirements

Level 1 Requirements

  • The robot will be designed to be a toy for people ages 8+.
  • In order to minimize manufacturing cost, and packaging cost the robot shall be able to be constructed from subassemblies within 10 minutes.
  • The robot shall incorporate 3D printed parts to demonstrate the feasibility of the 3DoT board for 3D printed robots.
  • For quick production of the prototype, the preliminary project shall be restricted to six hours of total printing time with a 2 hours limit for each single print.

Level 2 System Requirements

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

Update 3: Final 3D Model – Hexy Mk-02 (April 29, 2018)

Chassis

Bottom Plate 

Figure 1: Final Bottom Plate Design 

Design Changes

  • Removed the two wire tubes/wire holes.  This was done due to the inability to route all our wires through the two 8 mm holes (which we could not make bigger due to space). As well as, due to the interference of wires with our hardware because we had to place our hardware in the middle of the top panel too. Alternative methods were found to route our wire to the bottom plate below.
  • Reduced the width of our bottom plate by 12 mm. Since we removed the wire tubes from our bottom panel we were able to make our cam system fit in a smaller space making our design more compact than before.
  • Removed front and back extrusions. These extrusion were removed to provide support for the front sensor enclosure and the rear cable tube, which will be discussed shortly
Top Plate 

Figure 2: Final Top Plate Design 

Design Changes

  • Redesigned extrusions to give easy access to all screw in the bottom plate. In previous revisions of the top plate we saw that not all screws on the bottom plate could be easily reached with a screw driver. Therefore, a solution was to place holes over the screws to eliminate the need of removing the top panel for screw adjustments.
  • The area along the middle was configured to the width of the 3DoT board ~35 mm.
  • Added more space along the front to provide a mounting point for the sensor enclosure.
  • Added decorative fangs to the front to give is the aesthetics of a spider.

Legs

Femurs 

Figure 3: Final Femur Design 

Design Changes

  • Increased size of femur-to-tibia joint to prevent layer splitting in the PLA material.
  • Outer femurs, femur-to-tibia joints where re-designed to have an angled offset to provide more stability/balance while walking. The prototype design was having issue stabilizing its weight as it walked. After reviewing methods to solve this issue we found that the previous Spiderbot (3DoT David) had the same issue and solved it by offsetting the femur-to-gear joint in a similar way as shown below. If interested in seeing their solution see “Spring 2016: 3DoT David Design Evolution”.   This solution enabled us to configure all joints to the same width, therefore all legs will have the same tibia design.
Tibia 

Figure 4: Final Tibia Design 

Design Changes

  • Increased size of the Femur-to-Tibia joint to prevent PLA layer splitting.
  • Redesigned bottom tips to have thin rubber sheets rap around the tips for grip support while walking.  In a similar way as shown in the  Design Modifications Post.

Gear-to-Femurs Joints

Figure 5: Final Gear-to-Femur Design

Design Changes 

  • Increased Size of the joint and shape to provide exact fitment to femur end.
  • Increased hole size to 3.5 mm. As recommended by the customer, we will be fitting a 3 – .5 OD bushing with ID of 2.5. We will insert a 2.5 mm screw to increase stiffness of the femur-to-gear joint while at the same time allowing the femur to go up and down.

Sensors Enclosure

Figure 6: Sensor Enclosure Design

The hardware enclosure will house: One, 3 Pin Ultra Sonic Sensor, Three, Si1145 light sensors, and 3 LEDS. The Ultra sonic and light sensors will be inserted through the top opening, and the LEDs will be inserted through the rear. The bottom hole mounts will connect to the bottom plate and the top hole mounts will connect with the top plate.

Hardware Enclosure

Figure 7: Hardware Enclosure Design 

The top enclosure will give Hexy a better appearance, while at the same time concealing the hardware of our robot. The cover will have have openings for two LEDs that will act as eyes for our robot. There will be unique patterns designed in the top panel for our company logo and product name.

Figure 8: Hardware Enclosure Split in Half 

Do to the size of the cover, we will be splitting it into two parts in order to not exceed the 2 hour limit on single prints.

 

 

Figure 9: Wire Tube Design

The wire tube will act as our new method to route wires from the top to the bottom plate. The opening is 15×18 mm and should be big enough to route all a=our wires to the bottom plate without interfering with our design.

Final Assembly

The final assembly is depicted below with the colors we plan on working with.

Figure 10: Final Assembly Front View

Figure 11: Final Assembly Rear View 


Figure 12: Final Assembly Side View 

Figure 13: Final Assembly Top and Bottom View 

 

Update 2 (April 17, 2018)

Top Plate

Figure 14: New Top Plate Design 

Design Changes

  • Removed gear popping mechanism from top plate. Will just add spacers to the underside of the top plate to prevent driving gears from popping.
  • Added a face and holes for LEDs which will act as eyes for our spider. As requested by the customer, our Spiderbot needed to incorporate something to the top to make it stand out more and attract the eyes of the consumer.
  • Center width is designed to fit the 3DoT Board which is ~ 35 mm
  • Removed holes for wire routing. New hardware enclosure will include a route for wires. Also, having the wires routing through the center of the top plate would interfere with placement of hardware.

Hardware Enclosure

Figure 15: Hardware Enclosure 

The hardware enclosure will conceal our hardware (as most toys typically due) and will have a design similar to that of a spider’s abdomen

New Design Assembly

Figure 16: New Design 

 

Update 1 (April 10, 2018)

After reviewing our design with the professor and by analyzing the quality of Hexy Mk-01 we came up with the following design solutions that will solve the existing problems we have.

Chassis

Bottom Plate

Figure 17: Bottom Plate 

Design Changes: 

  • Removed all shaft extrusions for gears and leg guides. The reason for doing this is that these thin extrusions turned out to be very fragile when 3D printed, as explained in the assembly and fabrication blog post for 3DoT Hexy Mk-01. In multiple occasions, the manufacturing engineer (me) had to glue these thin shafts back in place. A better solution for this is to get rid of all the shafts and leave holes to insert more durable materials. Such as aluminum rods for the leg guide shafts and screws for the gear shafts.
  • For the leg shaft guides, we decided to make 3.5 mm holes and insert 3 mm aluminum rods which will be cut at the desired height.
  • For the gear shafts, we will leave 3.5 mm holes and do one of the following:
    • Use bearings, 3 mm machine screws, and nylon locking nuts to hold gears in place.
    • Use push rivets and gear inserts to hold gears in place.
  • Driving gear holes will be sized to 13 mm (biggest holes shown above) in diameter for easy insert of driving gear with motor attached from the bottom plate (driving gear is 11 mm in diameter).
  • Holes for leg shafts will be 3 mm in diameter (diameter of aluminum rods).
  • Wires tubes designed in the top plate will be shifted to the bottom plate and will have a height of 20 mm.
  •  Corner holes should be 3.5 mm in diameter.
  • Bottom plate thickness reduce by 2 mm to raise level of motors from ground.
  • Add extruded cuts for motor boxes that are 1.5 mm deep, as shown in the bottom view above.
  • Add holes for motor box mounting screws 3 mm in diameter.
Top Plate

Figure 18: Top Plate

Design Changes: 

  • Due to higher than expected 3D print times, we will redesign the top plate in order to have it be fabricated using a CNC machine. To do this, we will eliminate all extrusions that were present in 3DoT Hexy Mk-01. We will shift our wire tubes to the bottom plate and use a different technique to prevent the driving gear from popping off. A solution proposed by the manufacturing department is to make a three sided rectangular shaped cut out on the top plate and bend it to a degree such that the rectangle is preventing the driving gear from popping as shown below:

Figure 19: New Design for driving gear, gear capture 

  • Resized corner holes to 3.5 mm.
  • Resized leg guide holes to 5 mm in diameter with 2 mm depth.

Legs

Femurs

Figure 20: Three Types of Femurs we will use

 

Design Changes: 

  • Shifted holes that connect to gear joint 2 mm inward to prevent cotter pins from braking through material.
  • Rounded junction where femur-to-gear joint goes to implement new femur-to-gear joint design.
  • Increased depth of extrude cut contour on the underside of femurs by 1 mm in depth.
  • Increased all hole diameters to 2.5 mm.
  • Increased length of tibia-to-femur joint by 2 mm.
  • Rounded edges that tend to come in contact with the screws holding gears in place.
  • Increased femur thickness by 2 mm to give screw holes a better placement and to reduce the probability of inserted screws ripping through material.
Tibias

Figure 21: Two types of tibia

Design Changes: 

To all:

  • Increased tibia thickness by 2 mm to give screw hole a better placement so that when screw is inserted it wont rib through the material.
  • Got rid of narrow tips of legs and replaced them with 4.5 x 3 x 9 mm holes (length/width/depth) in order to add rubber inserts in the tips of the legs.
  • Increased hole size to to 2.5 mm.

Outer Tibia:

  • changed dimensions of center extruded cut to match that of the middle tibia, in order to make all legs have the same profile.

Gear-to-Femur joint

Figure 22: Gear-to-femur joints

 

Design Changes: 

Note: This design is based of the wooden joints designed during the rapid prototype.

  • New joint will be greater in diameter in the bottom (5 mm) this will provide enough space for 2 mm screw (which is the same as the diameter of the hole) to screw in without splitting open the material.
  • The hole which will connect femur to joint will be 2.5 mm.
  • The top is rounded to provide clearance for femurs when they are raced.
  • The diameter at the bottom is smaller than that of the top due to the smaller clearance available in gears when joints rotate on gears.

Prototype – 3DoT Hexy Mk-01 (March 15, 2018)

Note: Explanations will be a derivative from the explanations given in the preliminary design  document (under the mechanical drawing section). For measurements of each component that will be mentioned read the mechanical drawings document.

Chassis

The chassis of 3DoT Hexy will house: the cam system and legs, mounts for all electronic components, the lifting mechanism, and a safe passage for wires that must connect from the bottom panel to the top panel.

Bottom Plate

Figure 23: Bottom Plate 

This design is based of Sprint 2016’s 3DoT David design. The bottom plate will house the cam system that will mimic 3DoT Davids 3:1 gear ratio design, read “ Spring 2018 3DoT Hexy: Gear Design” document.  Ten shafts with 4mm diameter will be located at 21.125mm from the center axis. We will extrude cut patterns to reduce 3D print times while at the same time giving our design a unique and appealing view to distinguish it from 3DoT David. The lifting guides for the femurs will be angled. This is done in order to provide a smooth transition from ground to peak heights during the legs extension. For the holes found along the center axis: big holes will be used to run wires from top to bottom panel, and smaller holes will be used for driving motor connections. The design will have more holes upon determination of the position of the custom PCB board, battery, and 3DoT board.

 

Top Plate

Figure 24: Top Plate 

The top plate will share the same design as the bottom plate to give 3DoT Hexy a better appearance. It will be configured as a universal design, by this we mean that there will be no holes for mounting electronic components, and positioning of components can go wherever desired. Upon determination of all components being used and of their dimensions, the top plate will be reconfigured to accommodate those components in a future revision. For the most part, the top plate will be flat and showing only the extrusions. Looking at the bottom view, the small protruding shafts will be our gear captures (to keep the driving gears from popping) and the two tubes are there for wire management  from top panel to bottom panel. There are holes in each corner for the screw mounts that will hold the top and bottom panel together, and there are three 1 mm deep holes on each side in which the shafts of the lifting guides will sit. We will extrude cut patterns to reduce 3D print times while at the same time giving our design a unique and appealing view to distinguish it from 3DoT David. Lastly, it may be hard to see but the thickness of the plate increases as we move closer to the center of the plate (look at mechanical sketch), this is done to provide support for the femurs when they are in there inner state of motion. If that change in thickness wasn’t there, gravity will push the femurs up making the system unbalanced when walking.

Legs

Femurs

Figure 25: Three Types of Femurs 

As explained in “Spring 2018 3DoT Hexy: Improving 3DoT David Design”, the femurs will house a groove which will provide the transition from ground level to peak height level of the legs.

Tibias

Back/Front

Figure 26: Two types of tibias

The legs will be wider than those of 3DoT David due to the increase width, which is needed to increase contact point of femur-to-tibia joint. The result we can expect from this is increased 3D print times due to larger surface area of tibias. To try to fix this issue we trimmed the width of the tibias by 2mm (from 6mm to 4mm) and decided to shell/hollow out the tibias and cut out excess material by making an opening right down the middle. The legs have a 2mm holes that will align with the 2mm hole of the femur. Thread will be created through this joint and a screw will be placed through femur-to-tibia joint to prevent them from moving. The design of the middle tibia is different from that of back and front tibia, the reason for this is mainly due to aesthetics. Since the middle tibia will support most of the weight, it made sense to make it look stronger than the outer tibia. For this reason, a thinner extrusion and overall wider profile was assigned to the middle tibia. 

Additional Parts

The only other component that will need to be 3D printed will be the T-joints that connect the big gears to the femurs:

Figure 27: T-joints 

Dimensions for the T-joint are given in the mechanical sketch document

Cam Assembly

Figure 28: cam assembly generated in Solidworks 

Like 3DoT David’s Design, our model will follow a tripod stability model to keep the robot balanced while walking and to mimic a spider’s movement. The driving gear will be the blue D-shaped bore gears.

Completed Assembly of Hexy Mk-01

Figure 29: Finished Assembly of 3DoT Hexy Mk-01 for prototyping 

Simulation

Simulation of System Can be found by clicking the bottom link:

https://www.youtube.com/watch?v=DXkc-AGq5vk

 

Resources

  1. Spring 2018 3DoT Hexy: Mechanical Drawings
  2. Spring 2018 3DoT Hexy: Decision of Movement Mechanism
  3. Spring 2018 3DoT Hexy: Improving 3DoT David Design
  4. Spring 2018 3DoT Hexy: Determining Gear Design
  5. Spring 2018 3DoT Hexy: Preliminary Design Review

 

 

Spring 2018 3DoT Hexy: Getting 3DoT David Working

By: Kris Osuna (Electronics & Control Engineer) and Eduardo De La Cruz (Manufacturing Engineer)

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

Approved by: Miguel Garcia (Quality Assurance)

Introduction

Since we will be basing our design of Spring 2016’s 3DoT David, it is important that we get a good idea of how 3DoT Davids mechanism functions, as well as of how this mechanism will be interfacing with the 3DoT board and all attached peripherals.  Additionally, getting 3DoT David working will enable us to find areas that can be improved upon and may be applied as solutions in the development of our prototype. We will divide this blog post into two sections:  1. What was done by the manufacturing department and 2. What was done by E&C department.

Related Requirements

Level 2 Requirement

The robot will use a cam system identical to that of 3DoT David to drive the movement of the legs while navigating through the maze.

Manufacturing

By: Eduardo De La Cruz

Minor Repairs

Replaced Driving Gears

Figure 1: Added blue gears with D shaped bore 

The previous driving gears (gears tied to motor shafts)  where not turning the cam system. Therefore, a solution that the manufacturing department came up with was using gears with a smaller bore diameter and creating a D lock bore to prevent the gear from slipping from the motor shaft.  As seen above by the blue gear. 

 

Replaced a gear shaft with a screw

Figure 2: Added flat head screw as a replacement gear holder 

The current gear shafts are 3D printed and are very thin and fragile. A good replacement for this is a 3 mm screw with a hex nut holding it in place. To prevent the thread of the screw from messing up the gear bore, we sanded down the thread.

 

Added grease Figure 3: Red “N Tacky Grease 

The gears were having a hard time turning and would often lock. An attempt to fix this issue was to add Lucas Red “N” Tacky grease between the gears. Doing this actually improved cam system performance.

 

Conclusion

  • Need rubber tips or other material for leg tips, to prevent slipping when walking.
  • Needs better gear capture system. Current system is permanent (melting plastic gear shafts) which defies the current requirement of assembly and disassembly.

Figure 4: Melted Gear shafts 

  • Gear shafts are very fragile and can easily break. (Should pursue alternative solution than 3D printing gear shafts).  

 

  • Need to isolate wires from cam system. Wires susceptible to getting caught in gears Figure 5: Exposed Wires in cam 

 

  • Driving Gears often slip from motor shaft. Due to white insert not keeping motor shaft stiff enough. Figure 6: Current driving gears in 3DoT David 

 

  • Femur-to-tibia joint design not very reliable. Figure 7: 3DoT David’s leg joints 

 

  • To reduce friction between gear shafts and gear bore, it would be interesting to pursue alternative methods to make the gears rotate with less friction, such as using bearings and bushings.

Electronics & Control

By: Kris Osuna

Since the purpose of 3DoT David was laser tag, we were unable to put to good use the custom PCB that was designed by the team. Along with this issue there was also the issue of not having a 3DoT board to interface with. As a result, the Arduino Leonardo microcontroller board was used. The Leonardo was used because it is based on the ATmega32u4, which the 3DoT board uses as well. The Arduino Leonardo technical specifications can be found under references

 

E&C attached the hardware that is used in the lab sequence robot to see if it could walk forward, in reverse, and turn around. The ultrasonic sensor was also placed on the board as well to test for obstacle detection. The bluetooth HC-06 was placed on the board to check for connectivity.

 

E&C tested operation of 3DoT David lab sequences 1 and 2. We were able to get 3DoT David to walk straight, turn right, turn left, detect obstacles and be controlled via a cellphone with bluetooth. The software can be found under links.

 

Figure 8: 3DoT David with all hardware from the lab sequence robot 

Conclusion 

The sensors we have purchased work and can be implemented on a microcontroller using an ATmega32u4. The schematic and PCB can be made with the knowledge that all the sensors can work together. Wire management is going to be an issue because the UV sensors, LEDs, and ultrasonic sensors will have to be attached to wires. Manufacturing will be notified of the wire situation to try to find a way to hide the wires. The motor wires are too short and access to the wires is difficult due to being attached to the top plate. Manufacturing will be notified of this problem.

The ultrasound drops the distance reading to 0.0 inches causing 3DoT David to run the same task twice. A condition needs to be put to ignore when the reading drops to 0.0. The Bluetooth commands were not sent through the arxterra website but through a Bluetooth app. This may be due to our Bluetooth not having BLE support. A new Bluetooth module with BLE support was purchased

Resources

  1. https://store.arduino.cc/usa/arduino-leonardo-with-headers
  2. 3DoT David Working Code

Spring 2018 3DoT Hexy: Mechanical Drawings (Preliminary/Final)

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

Approved by: Miguel Garcia (Quality Assurance)

Introduction

Below are the sketches for our 3DoT Hexy design. Sketches are susceptible to change. All changes will be logged in this blog post in future iterations. The first iteration will be considered our preliminary design which we label as 3DoT Hexy Mk-01. Future revisions will be labeled as iteration “n”:  3DoT Hexy Mk-0n. Note this blog post does not contain reasoning or explanation for why things look the way they are, for that you should read  Spring 2018 3DoT Hexy: 3D Model. This blog post just contains the dimensions of all components that will be 3D printed.

3DoT Hexy Mk-02 (Final Design) – (April 28, 2018)

Chassis

Bottom Panel 

Figure 1: Bottom Plate Dimensions

Top Panel 

Figure 2: Top Plate Dimensions 

Femurs

3 Types of Femurs 

Figure 3: Three Types of Femurs 

 

Middle Femur Dimensions 

Figure 4: Middle Femur Dimensions

Outer Femurs Dimensions

Figure 5: Front Femur Dimensions 

Note: The back leg will have the same measurements with extrude-cut on opposite side.

Figure 6: Side View of femurs split in half showing Leg lifting ramp

Tibias

Figure 7: Tibia Dimensions

Femur-to-Gear Joints

Figure 8: Femur-to-Gear Joint Dimensions

Sensors Enclosure

Figure 9: Sensor Enclosure 

Figure 10: Front and Back View Dimensions 

Figure 11: Top and Bottom View Dimensions 

 

Figure 12: Side View Dimensions 

 

Figure 13: Front Split in half view  

Hardware Enclosure

Figure 14: Hardware Enclosure 

Figure 15: Side View Dimensions 

Figure 16: Top View Dimensions 

Figure 17: Split in Half View 

Wire Tube

Figure 18: Wire Tube Dimensions 

3DoT Hexy Mk-01 (Prototype) – (March 15, 2018)

 

Chassis

Bottom Panel

Figure 19: Bottom plate dimensions 

Top Panel

Figure 20: Top plate dimensions 

Femurs

3 Types of Femurs 

Middle leg                       Outer Legs

Figure 21: Femur Dimensions

Note: The back leg will have the same measurements with extrude-cut on opposite side.  

 

For all 3 femurs

Figure 22: Section view of leg lifting ramp in femurs

 

Tibias

4 Outer Tibia

Figure 23: Outer Tibia Dimensions 

2 Inner Tibia

Figure 24: Inner Tibia Dimensions 

T-Joints (Gear-to-Femur Joints)

The T-Joints will connect the gears to the femur using 2.5 mm screws

Figure 25: Dimensions of T-joints 

Spring 2018 3DoT Hexy: Project Planning and Scheduling

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

Approved by: Miguel Garcia (Quality Assurance)


Introduction

The purpose of this post is to compile the project schedule from start to finish for all task that need to be finished by each division. The schedule will practically mirror the time frames and due dates priorly established in the task matrix. The goal is to provide a visual reference of how far or close one is from reaching their deadlines for a given task. We will begin by first taking into account the time spent hiring, planning, and learning about the engineering method, then we will be breaking down the time frame it will take each division to complete their task, and lastly we will compile all this information into a project schedule using excel’s Gantt project planner.

Final Project Schedule (May 15, 2018)

Figure 1: Final Schedule 

Note: Task Labeled in red are task we never got too. Purple are task completed in time. Dark yellow are task completed past the due date. Light purple and light yellow are task that where never completed.

Figure 2: Final Burndown 

Blue = Current Progress, Orange = Desired Progress

From the burndown above, we can see that we ended up being 10 task behind.  Most of these task were related to hardware testing and software.

Links to:

Final Schedule:

Planner Final2.0

Final Burndown:

burndown

Preliminary Design Project Schedule (March 15, 2018)

Figure 1 : Project planner generated using excel’s Gantt project planner)

Dark purple represents our progress, light purple represents what needs to be done. If we exceed the due date the bar will turn orange. Orange lets us know how many days it was late.

Task for each division are color coded and their is a legend at the top explaining each color.

Note: Division members may take on task from other divisions if they see that they have the time available in their existing schedules to aid other divisions in getting their task done.

 

To get a closer look at the specific task in the above project planner, look at the excel spread sheet located in Resources.

Stage 1: Hiring & Picking a Project, Learning the Engineering Method, and Developing a Task Matrix

Week 1: Hiring & Picking a Project

    During this week students are introduced to the EE400D robot company, to all job positions available, and to the 6 projects that can be created. Students submit resumes and cover letters applying for a specific roles, form teams, and pick a project to tackle.

Week 2 – 3: Learning the Engineering Method

During this week students are introduced to a series of presentations that cover the engineering method. This method is a systematic approach used to reach a desired solution to a problem. Students will learn the six steps: developing ideas, concepts, planning, designing, development, and launching. Students will present a presentation on creativity development at anytime during these weeks. During this time we also develop project mission and level 1 requirements.  

Week 4 – 5: Developing a Task Matrix

Students will read existing blog post from previous semesters, scavenge for what can be reused and develop their own task matrix. The task matrix will require extensive research on what needs to be done by each division to make the project happen. The task matrix requires that students provide for each task: existing references, define what is its predecessor and what it is linked to, who will the task be assigned to, estimated time to complete, and the due date.

Stage 2: Division Specific Task

    From week 6 and onwards, each division will focus on completing task that are specific to their job description and that should already be defined in the task matrix.

Project Manager

Week 6

Preliminary Budget, Maze Definition

Week 7

Additional Robot Specific Mission Objectives, Planning & Scheduling, Work Breakdown structure.

Week 8

Preliminary Design Review Blog Post.

Week 9 – 15

Work on keeping everyone on schedule, work on Project Video, regularly update professor about progress, inform team members about changes, upload blog post.

Week 16

Final Blog Post, lessons learned.

Week 17

Project Video.

Mission, System, & Testing

Week 6

Project Specific Lvl. 1 & Lvl. 2 requirements.

Week 7

Verification Test Plan and Report, System Block Diagram, Product Breakdown Structure, Interface Matrix, Resource Report (Mass, Power, & Cost) , Robot Avoidance rules (Update), UV sensors.

Week 8

3D print times (preliminary), Mass (Preliminary), Preliminary Design Review Blog Post.

Week 9

cable tree and assembly diagram

Week 10 – 14

Work with E&C in implementing cable tree, system wiring, PCB layout, updating mass, power, and cost report, and creating the arxterra custom commands and telemetry on the App and Arduino.

Week 15

Final System Integration and Test.

Week 16

Final Verification.

Week 17

Execute mission

Electronics & Control

Week 6

Decision on Motor type selection.

Week 7

Prototype Fritzing Diagram, Power Estimate of Components, UV sensors study, RGB color sensors.

Week 8

Preliminary Design Review Blog Post, getting 3DoT David working.

Week 9

System Schematics (Eagle CAD), Sensor shield layout.

Week 10

Breadboard build and test.

Week 11

Integration Testing on final design, Electronic Component BOM and Order, Spiderbot line following code and demonstration.

Week 12

Robot avoidance general detailed algorithm, Spiderbot turning code and demonstration.  

Week 13

whichway code and demonstration, custom PCB Assembly and Fabrication

Week 14

Implementing robot avoidance code, Interfacing with 3DoT David or our model.

Week 15

Final Arduino Code, Final system Integration and testing.

Week 16

Last minute touch ups.   

Week 17

Execute mission

Manufacturing

Week 6

Research and obtain a reference model (Spring 2016:3DoT david design) from which to model your movement mechanism (not a task)   

Week 7

Mechanical Drawing, Decision on movement mechanism to implement, Determining gear design

Week 8

Improving 3DoT David Design, Preliminary sketch, Preliminary Design Review Blog Post  

Week 9

3D solidworks model

Week 10

stress testing  

Week 11

Decision on materials and fabrication methods, Manufacturing Prototype.

Week 12 – 13

Revisions, fabrication and assembly of PCB.    

Week 14

Final 3D Model.  

Week 15 – 17  

Aid in other task, last minute revisions on design (if any).

Preliminary Burndown (March 15, 2018)

The graph shows how task will be distributed over the course of the semester. The goal is to finish all task before execution of the mission.

Figure 2: Preliminary Burndown

Blue = Current Progress, Orange = Desired Progress

As off week 8, we have completed about half of the task defined in the task matrix. So far, we have submitted most if not all preliminary task documentations, and a few trade studies done by each division engineer showing their progress. For more details on what is due each week based on the above burndown read, “Spring 2018 3DoT Hexy: Project Planning and Scheduling”.

Resources

  1. https//drive.google.com/drive/folders/1XX5b3j3zwPvR-v6-B63a0Ad5g8Auu3_Y
  2. https://www.arxterra.com/wp-content/uploads/2018/04/Planner-Final2.0.xlsx