ECE 477 Digital Systems Senior Design Project Rev 9/12
Homework 4: Packaging Specifications and Design
Team Code Name: COST Robot______Group No. 7_____
Team Member Completing This Homework: Eric Osborne______
E-mail Address of Team Member: osbornee______@ purdue.edu
Evaluation:
SEC
/DESCRIPTION
/MAX
/SCORE
1.0 /Introduction
/5
/2.0 /
Commercial Product Packaging
/-
/2.1 /
<Product #1>
/10
/2.2 /
<Product #2>
/10
/3.0 /
Project Packaging Specifications
/20
/4.0 /
PCB Footprint Layout
/10
/5.0 /
Summary
/5
/6.0 /
List of References
/10
/App A /
Project Packaging Illustrations
/10
/App B /
Project Packaging Specifications
/10
/App C /
PCB Footprint Layout
/10
/TOTAL
/100
/Comments:
1.0 Introduction
In this project, the robot being designed will traverse a maze and map that maze out, while also determining where colored lights are inside the maze. Once finished mapping the maze it will revisit the colored lights in an order preordained by a user. It will then exit the maze and the user will be able to connect a USB cable from the robot to a computer to access a map of the maze. The maze design will not be open, but will only feature hallways. This will allow the robot to better map out and traverse the maze. To be able to achieve the different functions necessary for this project, the design uses 2 pushbuttons, 4 LEDs, 3 ultrasonic range sensors, 1 long range laser sensor, 2 wheels and motors, a color sensor, a battery pack, and a PCB. All of these things will need to be packaged into one small robot. The color sensor and range finders will need to have a clear line of vision, and the wheels will need to be able to be free to move. Also, the device will have to be able to make near zero point turns to make it through the maze. All of these factors as well as others have influenced decision making as to how to package this device.
2.0 Commercial Product Packaging
The COST Robot should be physically compact and able to easily navigate a small space. To better determine the packaging requirements for this design, two similar commercial products were analyzed: the Clocky Robotic Alarm and the iRobot Scooba 230 Floor Washing Robot. Both of these robots consist of small bodies on wheels. This general type of packaging is desired for the COST Robot.
2.1 Clocky Robotic Arm
Figure 1: Clocky Robotic Alarm
The idea behind the Clocky Robotic Alarm is simple, it is an alarm clock that rolls away from the user in the morning when it is time to wake up [1]. It appears from the video that it does not have the capability of smartly rolling away from the user, but instead uses random turns to make it harder for the user to catch it. While this product does not have the same functionality as the current project, it has a similar size and motion capability as the one being designed.
The layout of this design is fairly simple. The two wheels hold up the product and allow it to move. This also allows the body of the product to rotate around the wheels in the same way the wheels rotate next to the product to create movement. The two wheels allow for small zero point turns which is what we would like our product to have as well, but is not as stable because it is sitting on only two wheels.
The other part of this product is the full plastic shell which holds the logic of the device. The wheels allow the movement while the shell protects the circuit. This allows users to only see and interact with the parts they care about. Because of this you can see the screen, the buttons on the robot, and the wheels sticking out the side of the shell. This is a good idea for that type of product, but this project's robot will need sensors unblocked by the wheels. This will call for an open body above the wheels which will create a higher center of gravity. Hence, a stabilization wheel will be necessary.
2.2 iRobot Scooba 230 Floor Washing Robot
Figure 2: iRobot Scooba 230 Floor Washing Robot
The iRobot Scooba 230 Floor Washing Robot is a compact robot whose purpose is to “mop” small rooms such as bathrooms [2]. The robot is compact in size with a diameter of 6-1/2 inches and moves on two motorized wheels. It is designed such that it can clean hard-to-reach places, making accurate turns so as not to miss areas of the floor.
The Scooba 230 Robot implements a physical design similar to that of what the COST Robot will need. Both robots are compact – the Scooba at a diameter of about 6-1/2 inches and the COST Robot at a target diameter between four and five inches – and both utilize two motorized wheels for navigation. Furthermore, the COST Robot needs to be able to effectively travel throughout at maze, making accurate turns and having the ability to travel in a straight line. These are features exhibited by the Scooba. The robots differ in their primary “mission” during operation. The Scooba robot is designed to mop a floor without intelligent navigation while the COST Robot is designed to traverse a maze and then intelligently located pre-specified targets within the maze. In addition, the COST Robot will exhibit rather open packaging while the Scooba robot is fully enclosed in a plastic case.
In regards to packaging, the compact size of the Scooba robot is very beneficial as it aids in concise room navigation. The location of the wheels on the outside of the body is also a feature that the COST Robot will implement. As mentioned, the Scooba robot is enclosed in a plastic shell. For the COST Robot however, the outer packaging will be more open to avoid heat traps and eliminate the need for heat sinks in the design. Finally, the Scooba robot runs on a rechargeable battery which will be an additional requirement of our robot.
3.0 Project Packaging Specifications
As depicted in Figure 4 of Appendix A, the basic structural design of the COST Robot will consist of three octagonal platforms spaced an approximate distance of 1.5” apart from each other with the third octagonal platform being the PCB. The octagons will have a long diameter of 4”. An octagonal shape was chosen to limit the unnecessary need of plastic that may stick outside of the turning radius. These platforms will be supported by four posts located at each of the two front and back corners of the octagon.
The robot will move on two motorized wheels. The motor wheel combination can be seen in Figure 5 of Appendix A. The motors will lie on their sides on the bottom platform with the shaft sticking out away from the body of the robot. This will allow the wheels to be aligned parallel to each other along the octagonal shape of the robot body.
Figure 3 of Appendix A illustrates how the sensors and other peripherals are attached to the robot. Each of these attachments to the robot’s body can be seen in more detail in Figure 6. Each of the three short range sensors will be suspended from the bottom of the top platform. The color sensor will be located on the top of the middle platform facing outwards from one of the robot sides. The long range sensor will be located on the bottom layer, as will the battery pack.
The materials list for this design can be seen in Table 1 of Appendix B. This design is rather simple mechanically and will not require any special tools or machinery. The estimated weight of the COST Robot is 235.94 grams (~0.5 pound), with the bulk of this value coming from the battery, wheels, motor, and hard plastic platforms. As shown in Table 1, the approximate cost of this product is $165.91.
4.0 PCB Footprint Layout
As shown in Figure 7 of Appendix C, there are not many major components that will physically be on the project's PCB. Since all the sensors of the COST Robot need to be at different locations around the robot, these sensors cannot be mounted to the PCB. Instead, the PCB will have headers set aside for each sensor and have a few cables that connect to the PCB to branch out to each sensor.
Many of the sensors that do not lay on the PCB will be attached to pre-manufactured breakout boards. Of the major components that will have to be on the PCB, the footprints do not take up much room at all. The major components that need to be considered are the 44-pin QFP PIC18F4550, a QFN 24-MHz oscillator, the 16-pin DIP h-bridge, a USB port, and any headers needed to support the sensor components. The PIC had the capability of coming in a QFP or DIP package. The QFP was chosen for obvious reasons of being much smaller. When searching for oscillators, none could be found with a QFP footprint, so a QFN was chosen since it has a smaller area than a DIP design. The h-bridge could not be purchased in anything other than a DIP package. Since the h-bridge already met the design requirements and there was not a shortage of room on the PCB, the DIP package was chosen despite its large size. Last, since USB ports and headers have a standard size, there was no choosing between footprints.
In order to allow easy mounting through screws into each of the four posts on the robot, a regular octagon with a 4" diameter will be chosen for the size of the PCB. This will give enough room for analog parts of the circuit to be isolated from CMOS logic as well as ensure there is enough room for headers. The initial PCB layout can be seen in Appendix C.
5.0 Summary
The Clocky Robotic Alarm and the iRobot Scooba 230 have given packaging inspiration on how to design a near zero-point turn robot. The COST Robot will have a 4" diameter octagonal shape to make the robot more circular and avoid corner collision while turning. There will be two motorized wheels to drive the robot and one stabilization wheel since the robot's center of gravity will be higher than the two examples. Also, since the project robot has many more sensors on each side of the robot, the enclosure will be more open to avoid packaging interference and heat traps.
There will be three layers for components to be mounted. The bottom layer will have the motors, battery, and long range sensor attached to it. The middle layer will have the three short range sensors hanging from the top layer on the front, left, and right sides. On the left side, the color sensor will be mounted on the middle layer. The color sensor being on only the left side will not present a problem since the maze will have lights on both sides of the wall. The top layer will have the PCB mounted to it.
The PCB Footprint will be the same 4" regular octagonal shape as the layers of the COST Robot to allow easy mounting. The 4" octagonal area will be more than sufficient to house the major components - the PIC18F4550, 24-MHz Oscillator, h-bridge, USB port, and headers. The large PCB will also allow enough room to separate the analog and digital components of the circuit.
6.0 List of References
[1] Author Unknown. (2013). Clocky Robotic Alarm [Online]. Available: http://www.thinkgeek.com/product/91f2/?rkgid=275668648&cpg=ogpla&source=google_pla&gclid=CNScjfOvk7UCFbAWMgodpGMAJw
[2] Author Unknown. (2013). iRobot Scooba 230 Compact Floor-Washing Robot with Cleanser Packets [Online]. Available: http://www.hsn.com/products/irobot-scooba-230-compact-floor-washing-robot-with-clea/6495861
Appendix A: Project Packaging Illustrations
Figure 3: COST Robot Design
Figure 4: COST Robot Base Structure
Figure 5: COST Robot Motor and Wheel Design
Figure 6: COST Robot Interfacing
Appendix B: Project Packaging Specifications
Wheel / 2 / 16 / 32 / $7.98 / $15.90
Motor / 2 / 30.5 / 61
H-Bridge / 1 / *N/A / N/A / $2.35 / $2.35
Short Range Sensor / 3 / $10.60 / $31.80
Long Range Sensor / 1 / 4.8 / 4.8 / $14.95 / $14.95
Color Sensor / 1 / $14.95 / $14.95
Microchip PIC18F4550 / 1 / *N/A / N/A / $5.48 / $5.48
RGB LED / 1 / *N/A / N/A / $1.59 / $1.95
Compass / 1 / 0.14 / 0.14 / $34.95 / $34.95
Rechargeable Battery / 1 / 90 / 90 / $24.99 / $24.99
Fuel Gauge / 1 / *N/A / N/A / $2.80 / $2.80
Charging Circuit / 1 / *N/A / N/A / $2.80 / $2.80
Plastic Ball / 1 / *N/A / N/A / $2.99 / $2.99
Plastic platforms / 3 / 16 / 48 / $0.20 / $10.00
Total Mass: / 235.94 grams
Total Cost: / $165.91
Table 1: COST Robot Total Mass and Total Price
*Indicates the mass of the part is negligible and/or wasn’t able to be found
Appendix C: PCB Footprint Layout
Figure 7: PCB component placement
*PCB does not include circuit components related to recharging and fuel gauge. These items will be on a smaller PCB on the bottom layer of the robot.
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