Hardware
The hardware section of the robot consists of construction of the robot, as well as wiring and schematic work.
Component
selection
The construction and hardware design went as follows:
These steps will be briefly covered below:
Chassis Material Selection
After some initial research, the group narrowed down possible chassis material to Aluminum, Wood, Plexiglas and Lego. After setting up a decision matrix Plexiglas was chosen due to its ease of use and weight.
|
|
Weight (lbs. Per sq. ft.) |
Cost |
Ease of use (1-5) |
Overall Rating (1-5) |
|
Aluminum |
3.5 |
$32 |
3 |
3 |
|
Wood |
Less than 2lbs |
Less than $2 |
2 |
2 |
|
Plexiglas |
Less than 2lbs |
$2 |
5 |
5 |
|
LEGO |
variable |
$140 |
2 |
3 |
Weight Estimation
Appropriate weight estimation is necessary to determine the correct motor torque to use. The table below shows the weight of the major components as well as the total weight of the robot. The robot also needed to achieve a velocity of 2 ft/s. With this information it was possible find the correct motor torque to use.
|
Component |
Estimated
Weight |
|
Power Supply |
1.3 lb. |
|
Chassis |
1.0 lb. |
|
Wheels |
0.10 lb. |
|
Motors |
1.0 lb. |
|
Microcontroller |
0.3 lb. |
|
Other Components |
.3 lb. |
|
Total Weight |
4.0lbs. |
Motor Selection
Once the torque was known, it was important to decide what type of motor to use. There are three major choices: DC motors, Servo Motors, and Stepper Motors. After careful consideration, stepper motors were selected for the ONU design. This was mainly due to the fact of previous experience with stepper motors.
Microcontroller
Selection
The microcontroller is the “brains”
of the robot and is the most important piece.
Careful consideration was given to microcontroller selection. The table below shows all alternatives
considered.
Controller
Cost ($)
Memory (bytes)
Size (inches)
I/O Pins
Language
Ratings
(1-10)
School Stamp
30-40
256
1.5 x 0.75
8
PBASIC
2
Stamp 2SX
~90
2K-16K
1.5 x 0.75
16
PBASIC
5
Xilinx CPLD
129-149
128K
9 x 2
~40
Logic eqs.
5
ModCon
(HC11)
145
32K
3 x 2.5
~40
C, assembly
8
Mini (HC11)
+10
2048 (EEPROM)
3.1 x 1.9
~40
C, assembly
3
Handy (HC11)
200-300
32K
~5 x 3
~40
C, assembly
6
ONU used the ModCon HC11. This was mainly due to memory and I/O pins
available.
Sensor
Selection
Sensors are the “eyes” of the robot. They are used to detect walls and to correct
the robots direction. ONU chose the
Sharp GP2A200LCS shown at the right.
This was due to its long focal length (15mm) and the fact that Sharp
donated them to use. These IR sensors
also have a built in oscillator to filter ambient light.
Battery
Selection
Choosing the correct battery is important to insure that the robot
will be able to run for the 15 minutes allotted to compete. The table below shows the current draw of
the major components on the robot.
Component
Quantity
Voltage
Current Rating (mA)
Total Current (mA)
IR Sensor
8
5
30
240
HC11
1
5
32
32
Stepper Motor
2
12
400
800
LED
8
5
12
96
PLD
1
5
35
35
12V Battery
1
12
0
0
ULN2003a
2
-
0
0
Total Current
1203
As can bee seen from the table, the robot has a total current draw
of 1.2 amps. With this information, the
group chose a Lead-Acid Panasonic 12V 1.3Ah battery. The figure below shows the Duration of Discharge vs. Discharge
Current.
The approximate running time of the robot is 35 minutes, which is
ample for the competition.
Chassis
Design
Show below is the AutoCAD
drawings of the mouse that were used in construction
Front View
Side View
Motor
Control Design
To simplify code in the microcontroller, a Xilinx PLD was
implemented in the design to cycle through the motor states. The table and figure below show how the motor
works.
Phase
A
B
C
D
State1
1
1
0
0
State2
0
1
1
0
State3
0
0
1
1
State4
1
0
0
1
The VHDL code implements a state machine
that cycles through the four possible states of the motor under normal
operation as well as one additional state for default purposes. The four motor states are the four binary
patterns the motor will accept. The
table shows the possible states of the motor.
The figure shows how the motor coils are arranged inside the motor.
For state 1, coils A and B are
energized. The arrow denotes which way
the current will flow when the coil is energized. As can be seen from the figure, coil A will create a downward
force while coil B creates a right force.
This will produce a counter-clockwise motion. As the states progress in ascending order, the motor turns in a
counter-clockwise direction. If the
states progress in a descending order, the motors rotate clockwise. The direction case is handled by the LDIR
and RDIR signals. The pulse rate is
handled by the CLK pin, which is connected to the OC4 (output-compare 4) pin of
the HC11.
Overall
Schematic
Show below is a very simplified schematic of the robot. This shows how the HC11 is connected to the
sensor PCB and the Motor PCB.
The microcontroller is the “brains” of the robot and is the most important piece. Careful consideration was given to microcontroller selection. The table below shows all alternatives considered.
|
Controller |
Cost ($) |
Memory (bytes) |
Size (inches) |
I/O Pins |
Language |
Ratings (1-10) |
|
School Stamp |
30-40 |
256 |
1.5 x 0.75 |
8 |
PBASIC |
2 |
|
Stamp 2SX |
~90 |
2K-16K |
1.5 x 0.75 |
16 |
PBASIC |
5 |
|
Xilinx CPLD |
129-149 |
128K |
9 x 2 |
~40 |
Logic eqs. |
5 |
|
ModCon
(HC11) |
145 |
32K |
3 x 2.5 |
~40 |
C, assembly |
8 |
|
Mini (HC11) |
+10 |
2048 (EEPROM) |
3.1 x 1.9 |
~40 |
C, assembly |
3 |
|
Handy (HC11) |
200-300 |
32K |
~5 x 3 |
~40 |
C, assembly |
6 |
ONU used the ModCon HC11. This was mainly due to memory and I/O pins available.
Sensor
Selection
Sensors are the “eyes” of the robot. They are used to detect walls and to correct
the robots direction. ONU chose the
Sharp GP2A200LCS shown at the right.
This was due to its long focal length (15mm) and the fact that Sharp
donated them to use. These IR sensors
also have a built in oscillator to filter ambient light.
Battery
Selection
Choosing the correct battery is important to insure that the robot will be able to run for the 15 minutes allotted to compete. The table below shows the current draw of the major components on the robot.
|
Component |
Quantity |
Voltage |
Current Rating (mA) |
Total Current (mA) |
|
IR Sensor |
8 |
5 |
30 |
240 |
|
HC11 |
1 |
5 |
32 |
32 |
|
Stepper Motor |
2 |
12 |
400 |
800 |
|
LED |
8 |
5 |
12 |
96 |
|
PLD |
1 |
5 |
35 |
35 |
|
12V Battery |
1 |
12 |
0 |
0 |
|
ULN2003a |
2 |
- |
0 |
0 |
|
Total Current |
|
|
|
1203 |
As can bee seen from the table, the robot has a total current draw of 1.2 amps. With this information, the group chose a Lead-Acid Panasonic 12V 1.3Ah battery. The figure below shows the Duration of Discharge vs. Discharge Current.
The approximate running time of the robot is 35 minutes, which is ample for the competition.
Chassis
Design
Show below is the AutoCAD drawings of the mouse that were used in construction
Front View
Side View
Motor
Control Design
To simplify code in the microcontroller, a Xilinx PLD was implemented in the design to cycle through the motor states. The table and figure below show how the motor works.
|
Phase |
A |
B |
C |
D |
|
State1 |
1 |
1 |
0 |
0 |
|
State2 |
0 |
1 |
1 |
0 |
|
State3 |
0 |
0 |
1 |
1 |
|
State4 |
1 |
0 |
0 |
1 |
The VHDL code implements a state machine
that cycles through the four possible states of the motor under normal
operation as well as one additional state for default purposes. The four motor states are the four binary
patterns the motor will accept. The
table shows the possible states of the motor.
The figure shows how the motor coils are arranged inside the motor.
For state 1, coils A and B are
energized. The arrow denotes which way
the current will flow when the coil is energized. As can be seen from the figure, coil A will create a downward
force while coil B creates a right force.
This will produce a counter-clockwise motion. As the states progress in ascending order, the motor turns in a
counter-clockwise direction. If the
states progress in a descending order, the motors rotate clockwise. The direction case is handled by the LDIR
and RDIR signals. The pulse rate is
handled by the CLK pin, which is connected to the OC4 (output-compare 4) pin of
the HC11.
Overall
Schematic
Show below is a very simplified schematic of the robot. This shows how the HC11 is connected to the sensor PCB and the Motor PCB.