ECE 477
Digital Systems Senior Design Project
Fall 2005
Homework 3: Design Constraint Analysis and Component Selection Rationale
Due: Thursday, September 15, at Classtime
Team Code Name: ________Fire in the Hole__________________________ Group No. ___1___
Team Member Completing This Homework: ___Chad Carrie _____________________________
NOTE: This is the first in a series of four “professional component” homework assignments,
each of which is to be completed by one team member. The completed homework will count
for 10% of the team member’s individual grade. It should be a minimum of five printed pages.
Report Outline:
 Introduction (brief description of design project, with a focus on design constraint issues)
 Analysis of “real world” design constraints pertaining to your project
o computation requirements
o interface (sensors/actuators/peripherals) requirements
o power supply constraints
o packaging (size/weight) constraints
o cost constraints
 Rationale for component selection (a detailed comparison of at least two candidates for each
major component choice – show how the design constraints, outlined above, have driven or
guided your component choices)
 List of major components (Excel spreadsheet listing vendor, part number, unit cost, quantity,
and total cost)
 List of References (include links to data sheets for all components discussed – be sure to cite all
references in the body of your report, using standard IEEE format)
Evaluation:
Component/Criterion
Score
Multiplier
Introduction
0 1 2 3 4 5 6 7 8 9 10
X1
Analysis of Design Constraints
0 1 2 3 4 5 6 7 8 9 10
X3
Rationale for Component Selection
0 1 2 3 4 5 6 7 8 9 10
X3
List of Major Components
0 1 2 3 4 5 6 7 8 9 10
X1
List of References
0 1 2 3 4 5 6 7 8 9 10
X1
Technical Writing Style
0 1 2 3 4 5 6 7 8 9 10
X1
TOTAL
Include this sheet as a cover page for your report
Points
ECE 477
Digital Systems Senior Design Project
Fall 2005
Introduction:
The Hummer W2 (“W” for water) is a semi-autonomous robot that will be controlled by a
person over a wireless web interface. The person will then be able to see what the robot sees from the
wireless webcam [1]. A water cannon will be mounted on top of the robot. The cannon will have two
axis of movement: pan (on the horizontal plane) and tilt (on the vertical plane). The water pressure will
come from a 30 psi water pump [2]. Infrared sensors [3],[4] will be mounted at various locations on the
robot to be able to detect an object in its proximity. The sensor info can then be used in two ways. The
first way is to autonomously avoid collision with objects such as people or walls. The second way is that
if a person is close to the robot, the water cannon mounted on top could point in that general direction.
The word “could” is used because there will be two modes: Auto-Aim, which is the second way that
infrared data could be used, and Manual mode, which does not automatically aim the water cannon
when an object is detected. The control interface will allow the user to control: the movement of the
robot (forward/reverse and steering) via keyboard connected to a PC, the water cannon aiming servos
(pan and tilt) [5] via mouse connected to a PC, the water pump[2] for shooting water, and to switch
between the two aiming modes. The web interface will also contain the video signal from the wireless
webcam [1].
Analysis of “real world” design constraints:
Computational Requirements:
The processor will perform the following tasks:

Perform actions based on the commands given from the webpage

Control the drivetrain of the robot (steering and forward/reverse)

Use infrared sensor [3],[4] data to avoid collisions

Communicate with the infrared sensors [3],[4] to react appropriately to the data

Control the water cannon aiming servos (pan and tilt) [5]

Control the switching of the water cannon pump [2] (on/off)
Since the video feed from the webcam [1] will be broadcast over 802.11b via TCP/IP, the
amount of time the processor takes to react to the commands of a user is critical to avoid collision with
an object. A small delay from what happens in real life to the web interface on a computer may cause a
collision of the vehicle with an object. A clock speed of at least 10 Mhz will be needed in order to react
ECE 477
Digital Systems Senior Design Project
Fall 2005
quickly to the commands from the user as well as monitor the infrared sensors [3],[4], control the water
cannon aiming servos [5], control the water pump[2], and control the drivetrain.
Interface Requirements:
This project interfaces with many external components. The processor will need several general
purpose I/O pins and pulse-width-modulators. A wireless internet bridge will be needed to make the
project available over the wireless network. Since processors that support Ethernet have specific pins
dedicated to Ethernet, this will not have an effect on the total number of I/O pins needed.
Component
Interface Required
Infrared Sensors (Front and Back of robot) [3]
General Purpose I/O (6)
Infrared Sensors (Sides) [4]
ATD (2)
Motor
PWM (1) & General Purpose I/O (1)
Steering Servo
PWM (1)
Pan/Tilt servos for water cannon [5]
PWM (2)
Headlight
General Purpose I/O (1)
Water pump [2]
General Purpose I/O (1)
Table 1: Interface Requirements
The infrared sensors [3] for the front and the infrared sensors for the back of the robot will each
need three general purpose I/O pins. Two pins will be need for the left and right channel enable and one
pin will be need for the output of the infrared detector. The infrared sensors [4] for the sides will require
an ATD (one channel for each side).
One PWM and one general I/O pin will be needed to control the forward/reverse direction of the
motor. The PWM influences speed control and the I/O pin will control the direction of the motor. The
steering servo will need a PWM to control the direction of the front wheels. The PWM will control the
position of the steering servo.
Two PWM’s will be needed to control the pan/tilt servos [5]. One PWM will drive the servo that
controls the horizontal plane and the other PWM will drive the servo that controls the vertical plane. The
PWM’s will control the position of the pan/tilt servos [5].
ECE 477
Digital Systems Senior Design Project
Fall 2005
Additional I/O’s will be needed for the headlights and the water pump [2]. One general purpose
I/O pin will be needed to turn the headlights on and off. Another general purpose I/O will be needed to
turn the water pump [2] on and off.
Power Supply Constraints:
Since the car will be controlled remotely and will be powered completely by battery, power
consumption is an important matter to address. The servos for the pan/tilt [5], the servo for the steering,
the motor, the wireless webcam [1], the wireless bridge, and the water pump [2] will all draw a
considerable amount of power. The drive motor and the steering servo will both run on 9.6VDC
supplied by a 600mAh NiCad battery. The webcam [1], the infrared sensors [3],[4], the pan/tilt servos
[5], and the wireless bridge all require 5VDC. The water pump [2] requires 12VDC. The microcontroller
[6] requires 3.3VDC, which will be regulated from the +5V Digital supply rail.
Component
Quantity
V (V)
I (A) Max
Supply Rail
Microcontroller [6]
1
3.15 – 3.45
~ 0.3
+5V Digital
Wireless Webcam [1]
1
5
*0.9
+5V Digital
IR sensors (Front and Back) [3]
2
5
~0.005
+5V Digital
IR sensors (Sides) [4]
2
5
0.04
+5V Digital
Water pump [2]
1
12
0.53
+12V Analog
Motor
1
19.6
1
+19.6V
Analog
Steering Servo
1
19.6
0.2
+19.6V
Analog
Wireless Bridge
1
5
~ 0.5
+5V Digital
Pan/Tilt servos [5]
1
5
*1
+5V Analog
Table 2: Power Supply Constraint s
Supply Rail
Total Current Draw (A) Max
+19.6VDC Analog
1.3
+12VDC Analog
0.53
+5VDC Digital
**1.745
ECE 477
Digital Systems Senior Design Project
+5VDC Analog
Fall 2005
**1
Table 3: Power Supply Constraint Totals
The Hummer W2 will be powered by a 19.6VDC rechargeable battery pack and a 12VDC
rechargeable battery pack. The 19.6VDC battery pack is included with our robot platform [7] and will be
used only to drive and steer the robot. This battery pack is NiCad and rated at 600mAh and is advertised
as being able to operate for about 30 minutes. Given this data, the current draw for the motor and the
steering servo can be approximated. The 12VDC battery pack will be used to power everything else.
Regulators will be used to get the proper voltages for each individual component. One regulator will be
used for the +5VDC Digital power rail and one regulator will be used to power the +5VDC Analog
power rail. In Figures 2 and 3, the current draw ratings are somewhat deceiving. Since all devices will
not be on continuously, the power requirement for the 12VDC battery pack could be reduced
significantly. Also, the current ratings for the Wireless Webcam [1] and for the pan tilt servos [5] (given
by “*” in Table 2) are approximations. The exact currents are not known yet because the data sheets for
the devices do not list the current ratings. This lack of data causes the total currents for each supply rail
(given by “**” in Table 3) to be inaccurate. In order to make sure that the device is capable of driving
everything simultaneously, a battery pack will be chosen to power the entire robot as if every device was
using power. Since a significant amount of current will be drawn from the 12VDC battery pack, the
device may not be able to be run for long periods without spending a lot of money for a long duration
battery.
Packaging Constraints:
The Hummer W2 is a large robot, since it carries water on board as well as holding the sensors,
wireless bridge, microcontroller [6], sensors [3],[4], water pump [2], pan/tilt servos [5], battery pack,
motor, and steering servo. Our group has opted to buy a radio controlled “1:6 R/C Full-Function
"Tricked" Hummer – Black” [7] pre-built ($100). This option has a platform, driving motor, steering
servos, large wheels, and a plastic shell included. The driving motor and steering servos are already
custom mounted. The frame of the vehicle is quite large and provides plenty of room to mount all the
components needed for this project. The shell of the car is quite tall and will allow everything to fit
underneath. The pan/tilt servos [5] for the water cannon and the wireless camera [1] will be mounted on
the outside of shell. A way will have to be provided to allow quick access to the 12VDC battery pack
and the water container.
ECE 477
Digital Systems Senior Design Project
Fall 2005
Cost Constraints:
Since the intended audience is upper-class children, the chief cost constraint is to keep the
overall cost of the robot somewhat low without compromising functionality. In view of the fact that this
product will have a small consumer base, functionality will be given priority over cost. In choosing the
water pump [2] though, cost was as much relevant as was functionality. The ideal water pump would
have been the KNF NF1.11 [8] diaphragm pump, but the Hargraves LTC W311-11 [2] was chosen. This
is due to the fact that KNF diaphragm pump [8] was almost too much pressure than was needed,
especially for the cost of $287 compared to the Hargraves diaphragm pump [2] cost of $106. More detail
is given in the section below. The estimated prototyping cost will be $500 - $600.
Rationale for Component Selection
There are several major components that need to be considered in component selection: the
microcontroller, the water pump, the vehicle, the pan/tilt servos, the webcam, and the battery.
Microcontroller:
Since the microcontroller is the heart of the robot, properly selecting right component is vital.
The processor needs to have a semi-fast clock speed of at least 10 Mhz, an Ethernet interface, and plenty
of general purpose I/O pins. Having such a need for an Ethernet interface, the processor selection was
narrowed down to two different microcontrollers: the Freescale MC9S12NE64 Microcontroller [6] and
the Rabbit RCM3200 [9].
Both microcontrollers have plenty of general purpose I/O pins and both have the Ethernet
interface. The main comparison pertinent to the project is shown below in Table 4.
Rabbit RCM3200 [9]
Freescale MC9S12NE64 (80pin package) [6]
44.2 Mhz
25 Mhz
52 (44 general purpose)
48 (38 general purpose)
512k program + 256k data
8k
Flash
512k
64k
PWM
4
4
ATD
NA
8
Cost
$89
$17.24 (Free Samples available)
Clock Speed
I/O pins
SRAM size
Table 4: Microcontroller Comparison
ECE 477
Digital Systems Senior Design Project
Fall 2005
Since the Rabbit processor [9] does not have an ATD, the choice is simple. Without an ATD, the
infrared sensors for the sides will not interface properly. The Freescale MC9S12NE64 [6] must be used
for our project. The 80-pin package for this processor is more efficient than using the alternative 120-pin
package, because the extra general purpose I/O pins in the 120-pin package are not needed.
Water Pump:
The water pump is what allows the robot to shoot or spray the water. Two main water pumps
were considered: the Hargraves Advanced Fluidic Solutions LTC W311-11 [2] diaphragm pump and the
KNF NF1.11 [8] diaphragm pump. A table of the different specifications for the two pumps is shown
below.
Hargraves LTC W311-11 [2]
KNF NF1.11 [8]
Voltage (V)
12
12
Water pressure (continuous psi)
30
85
Current draw (A @ full load)
.53
.21
Milliliters/minute (mLPM)
320
100
Cost
$106
$287
Table 5: Water Pump Comparison
After consulting one of the engineers at Hargraves Fluidics, it was determined that at 30 psi,
water could be sprayed about five feet depending on the different nozzles at the end of the water hose.
Using this input as a guide, it was determined that the 85 psi capability of the KNF NF1.11 [8] was too
much pressure for the cost. The KNF NF1.11 [8] would be ideal if money was not an object and the
robot was designed to shoot at a much longer distance. The current draw of the KNF NF1.11 [8] would
also be more ideal.
Water Cannon Turret:
The two main options for having a turret for the water cannon to mount on were: the Pan/Tilt
Turret [5] and to make a turret from scratch from two servos. The obvious advantage and main reason of
using a turret pre-built is that the mechanical aspect of building one would not have to be addressed.
Also, given that the turret is not very expensive ($32.95), the price is well worth the time saved from
building a turret from scratch.
ECE 477
Digital Systems Senior Design Project
Fall 2005
The Vehicle:
The main concerns for choosing a vehicle platform were space availability and stability.
The three options that were considered when choosing a platform were: the 1:6 R/C Full-Function
"Tricked" Hummer – Black [7], the ATR Base Kit [10], and to build one from scratch.
Full-Function Hummer [7]
ATR Base Kit [10]
Built from Scratch
Price
$100
$139
~$100
Size
Very Large
Small/Medium
Custom
Stability
High
Low/Medium
Custom
Battery Pack
19.6V NiCad
NA
Custom
Table 6: Vehicle Comparison
Starting with the ATR Base Kit [10], there are two problems: size and stability. The overall size
of the vehicle is fairly small with only about an eight inch base. With such a small base, a concern was
raised about the stability if water and other components were attached to the vehicle. When the vehicle
stops, the vehicle may have the tendency to tip over. In addition to these two problems, this vehicle costs
more than the other two options even though it does not include a battery pack.
The “Built from Scratch” vehicle was estimated to cost $100. The following would be needed to
build a vehicle platform: 2 motors or servos, plywood or fiber glass, an H-bridge or servo controller,
wheels, and other miscellaneous hardware. The time to build this vehicle would be significant and just
as costly as the other two options.
The 1:6 R/C Full-Function "Tricked" Hummer – Black [7] is the best option. This vehicle is very
large with plenty of mounting space. It also includes: a battery pack (with charging station), a motor, a
H-bridge, steering servo, and a servo controller. This is all included at a price less than the ATR Base
Kit [10] and is comparable to the price of the “Built from Scratch” vehicle option. As an added bonus,
the Full-Function Hummer [7] also includes a nice plastic shell to cover the robot.
The Internet Camera:
The two internet cameras that were compared were the D-Link 2.4 GHz Wireless Internet
Camera [11] and the Linksys WVC11B Wireless-B Internet Video Camera [1]. The main reason for
choosing the Linksys Webcam [1] over the the D-Link Webcam [11] were the costs of $60 and $119
ECE 477
Digital Systems Senior Design Project
Fall 2005
respectively. Both webcams were capable of broadcasting over 802.11b wireless format therefore
eliminating the need for the microcontroller to do any video processing. Both were also capable of at
least 15 fps (frames/second) which would be a reasonable frame rate to drive the vehicle given that there
is inherent delay over a TCP/IP internet connection. The Linksys camera [1] is much cheaper so it was
chosen to be used in the robot.
The Battery:
Since the Hummer [7] already has a battery pack for its motor and steering servo, only a
rechargeable battery for the +12VDC supply rail will be needed. It is calculated that if the robot is
pulling a full load (every load turned on), the robot will draw approximately 3.275 amps. The project
needs as large a battery as possible without adding much weight (or cost). Given that the battery pack
for the Hummer [7] is supposed to last about 25 minutes, the 12VDC battery should last that long or
longer as well. The two batteries to be considered are the Sanyo KR1400AE [12] and the Sanyo
KR1500SC [13]. The KR1400AE [12] (costing $47.50) would last approximately 25.6 minutes and the
KR1500SC [13] (costing $52.50) would last approximately 27 minutes. The KR1400AE will be used
because the extra minute would not be worth the extra $5.
The List of Major Components is attached.
List of References:
[1] Linksys WVC11B Wireless-B Internet Video Camera
http://www.linksys.com/servlet/Satellite?childpagename=US%2FLayout&packedargs=c%3DL_
Product_C2%26cid%3D1115416831284%26site%3DUS&pagename=Linksys%2FCommon%2
FVisitorWrapper
[2] Hargraves Advanced Fluidic Solutions LTC W311-11 diaphragm pump
http://www.hargravesfluidics.com/pdf/LTC/W311-11_Rev_B.pdf
[3] LynxMotion IRPD Ver 2.0 Infrared Proximity Detector Datasheet
http://www.robotstore.com/download/3-573_IRPD_specs.pdf
[4] Fairchild Phototransistor Reflective Object Sensors
http://www.junun.org/MarkIII/datasheets/QRB113x.pdf
[5] Pan/Tilt Turret for Devantech SRF0x Ultrasonic Sensors
ECE 477
Digital Systems Senior Design Project
Fall 2005
http://www.budgetrobotics.com/shop/index.php?shop=1&cart=256087&itemid=256
[6] Freescale MC9S12NE64 Microcontroller
http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MC9S12NE64&nodeId=01
62468636K100
[7] 1:6 R/C Full-Function "Tricked" Hummer - Black
http://www.walmart.com/catalog/product.gsp?product_id=3933520
[8] KNF NF1.11 diaphragm pump
http://www.knf.com/pdfs/nf10.pdf
[9] Rabbit RCM3200 Rabbitcore
http://www.rabbitsemiconductor.com/products/rcm3200/index.shtml
[10] ATR Base Kit
http://www.active-robots.com/products/platforms/atr-base.shtml
[11] D-Link 2.4 GHz Wireless Internet Camera
http://www.dlink.com/products/resource.asp?pid=297&rid=943&sec=0
[12] Sanyo KR1400AE
http://www.sanyo.com/batteries/specs.cfm (model search for KR-1400AE)
[13] Sanyo KR1500SC
http://www.sanyo.com/batteries/specs.cfm (model search for KR-1500SC)