Group 6 Rene A. Gajardo Do Kim Jorge L. Morales Siddharth
Padhi
Slide 2
Motivation Heavy course work would require more materials.
Posture is affected by the larger amount of things that a student
carries. Knight Gear would allow for easier moving of school
materials and more.
Slide 3
Goals and Objectives Easy to use robot that follows the user
using tracking algorithm. Carry a limited load of materials for the
user. Onboard ultrasound sensors
Micro controllers One central microcontroller All the heavy
computing Sensors Motors, and accessories. Does not need to be very
powerful, but enough to be able to handle and process all incoming
data Data is simplified by the smaller, weaker, outer
microcontrollers which handle the analog I/O from the devices.
Slide 7
Micro Controller Comparison MC68332Intel 8051PIC 18F452 Atmega
2560 Digital I/O1524 54 Analog I/O158816 Operating Voltage
5V3.3V5.5V3.3V Cost$11.94$1.50$4.68$17.98
Slide 8
Why ATMega 2560 ? Popular option amongst hobbyist with a large
community for assistance Programmable in C using Arduino Enough
memory for our needs Allows Knight Gear to fully use all the Pulse
Wave Modulation lines that it required for all of the ultrasound
sensors and for the motor drivers. With a 3.3 volt operating
voltage, 54 digital I/O pins, 15 of them being PWM, 16 analog
inputs, and a large amount of documentation
Slide 9
Pin connections of Mega Pro 3.3
Slide 10
Ultrasonic Proximity Sensor It engenders high frequency sound
waves (above 20,000 Hz), which is incorporated in these sensors, to
measure the echo encountered by the detector, and is then received
after reflecting back from the target. This is the basic concept of
how Knight Gear will detect and follow its user.
Slide 11
ProductsResolution Reading Rate Maximum Range Required Voltage
Required Current Operational Temperature Price XL- MaxSonar -EZ
1cm10Hz300in-420in3.5V-5.5V3.4mA0C 65C$27.95 XL- MaxSonar -AE 1
cm10Hz300in-420in3.5V-5.5V3.4mA- 40C 70C$29.95 LV- MaxSonar -EZ 1
cm20Hz254in2.5V-5.5V2.0mA-$21.95 HRLV MaxSonar -EZ 1
mm10Hz195in2.5V-5.5V3.1mA0C 65C$28.95 Parallax PING))) 28015 1
cm10Hz118in5 V30mA0C 70C$29.99
Slide 12
Why PING))) 28015 ? Precise, non-contact distance measurements.
It is relatively easy to connect to microcontrollers PING))) 28015
measures distance from about 2 cm (0.8 inches) to 3 meters (3.3
yards). Robot side only receive signals, so cover the transmitter
User side only send signals, so cover the receiver Sensors from
Maxbotix Parallax Ping Sensor
Slide 13
Wireless Communication Wireless communication is needed for
localization of the user (which is the main feature of Knight Gear
and its top priority). Some wireless communications looked at were:
Wi-Fi Bluetooth, and ZigBee ZigBee turns out to be the final choice
for wireless communication in Knight Gear.
Slide 14
Zigbee Low cost, low power, wireless mesh network. The
following are the parameters of Zigbee ParametersZigBee Range10-100
meters Operating Frequency2.4 GHz ComplexityLow Power
ConsumptionLow
Slide 15
Zigbee contd Zigbee comes in 2 series. The following is the
comparison table between Series 1 and Series 2: ParametersXBee
Series 1XBee Series 2 Range300 ft.400 ft. Power Consumption 50mA @
3.3v40mA @ 3.3v Frequency2.4 GHz Data Rate250 kps
Cost$22.95$20.95
Slide 16
PNP Inverter We needed to invert a serial signal from low to
high using a PNP inverter. Using the serial out on the XBee and
inverting it, we can get a high pulse trigger for the PING
sensor
Slide 17
Solar Panel Increasingly popular No environmental pollution No
need of burning fossil to generate the electricity Solar energy is
no harm to our environment Generates electricity with no cost.
Slide 18
Solar Panel contd The material of the panel was important due
to the different efficiencies of different materials in
transforming solar energy into electricity. There are several
different types of solar panel in used today. Some of the solar
panels suitable for Knight Gear were the following: Monocrystalline
Polycrystalline Amorphous
Slide 19
Solar Panel contd Monocrystalline Most efficient (13-17%) These
are one of the oldest and most sturdy ones Expensive, require extra
time and energy Polycrystalline Efficiency (11-15%) One generally
needs a larger polycrystalline solar panel to match the power
output of a monocrystalline solar panel. Less expensive than
monocrystalline
Slide 20
Solar Panel contd Amorphous Non-crystalline silicon Amorphous
solar panels are most found in calculators. The efficiency of
amorphous photovoltaic cell is only about 6-8%.
Slide 21
So, which one ? Polycrystalline solar panels To build our
battery recharger for Knight Gear Even though this is less
efficient than monocrystalline panels It is very cost
effective.
Slide 22
Wheels Configuration Mechanisms to provide locomotion that is
required for the Knight Gear Differential Drive Ackerman Drive
Synchronous Drive, and Omnidirectional Drive
Slide 23
Differential Drive Wheels rotate at different speeds when
turning around the corners It controls the speed of individual
wheels to provide directionality in robot Correction Factor may be
needed to fix the excess number of rotations
Slide 24
Chassis Custom made chassis designed out of High Density
Polyethylene (HDPE). Most chassis found where either too small or
too big for our needs. Withstands heat Water-resistant
ParametersMeasurements Length19.5 in Width15.5 in Height (max)21.75
in Height (min)12 in
Slide 25
Chassis contd
Slide 26
Control Algorithm We implement a PI controller instead of a PID
controller to save memory. Runs only on current error and integral
of previous errors. Using small constant multipliers to lower the
deviation on Knight Gear. The error is determined by the time it
takes for the signal in the users transmitter to reach both sensors
on Knight Gear.
Slide 27
Control Algorithm Contd The microcontroller pings the radio
frequency antenna on the user side transmitter The user side
transmitter then makes its Ping))) sensor emit an ultrasound wave
The ultrasound sensors on the robot pick up on the ultrasonic wave
The sensors return how far away the user is according to each The
data is then sent to the PI Controller
Slide 28
Class Diagram of Knight Gears Control Algorithm
Slide 29
Overall code The robot turns in the direction of the of the
sensor which detected the signal first. The magnitude of the turn
and the speed of the robot is calculated by the difference in time
in which the sensors detect the user.
Slide 30
Motors Geared DC Motors Bigger, more powerful version of DC
motor Used in robotics and other control situations where a small
motor with lots of power is needed. The speed is generally
controlled using pulse width modulation of the fixed input voltage.
Can operate in both clockwise and counter clockwise Speed can be
altered by varying the voltage applied to the motor.
Slide 31
Motors cont Spur DC geared motors (x4) DC motor combined with a
gearbox that work to decrease the motors speed but increase the
torque Pololus metal gear motor:
Slide 32
Motor controller Microcontroller can decide the speed and
direction of the motor, but provide very limited and small output
current. Motor controller provides enough current and voltage to
the motor However, they cannot control how fast the motor should
spin. Therefore motor controller and microcontroller need to work
together to make the motors to move properly.
Slide 33
Motor Controller H Bridge H bridge circuit is commonly used in
robotics and other applications to allow the DC motors to run
forward and backward 0 1 1 0
Slide 34
ModelL293DSN754410DRV8833 Brand Texas Instrument/
Stmicroelectrics Texas Instrument Operating supply voltages 4.5V ~
36V 2.7V ~ 10.8V Tolerant peak output currents 1.2A2A1A Continuous
currents per each channel 600mA1.1A500mA H-BridgesQuadruple-Half
Dual Control methodPWM I 2 C / PWM Internal diodesYES Price (from
mouser electronic website) $1.12$0.87$2.58
Slide 35
Why SN754410 motor controller ? Quadruple-Half h-bridge circuit
-> control up to two motors Provides sufficient continuous
current of 1.1A Provides peak output current of 2A which is same as
the stall current of the motors No extra diodes are needed that
makes easy to implement the circuit Cost effective
Slide 36
Power source Rechargeable battery selection
NiCadNiMHAlkalineLi-ion Voltage1.25 1.503.6 Capacity loadLowHigh
Recharge Cycle 1000500 - 100010 - 50300 1000 Charging Time 1 - 1.5
hours2 -4 hours2 3 hours2 4 hours Discharge Efficiency 70 90 %66
%Varied by Capacity Load 80 90 Operating Temperature -20 45 C -20
60 C0 45 C Self Discharge Rate 10%25%
Power system power regulation cont. Block diagram of power
system 9.6V 2200mAH battery pack DC geared Motors 6V 2100mAH
battery pack Switch 6V -> 5V LDO regulator (LM2940) Microcontr
oller Motor driver IC Ultrasonic sensors 5V -> 3.3V LDO
regulator (LM3940) Xbee RF module (wireless antenna)
Slide 41
Power system power regulation cont. Block diagram of power
system cont. 6V 2100 mAH battery pack Switch 6V ->5V regulator
(LM2940) Ultrasonic sensor 5V -> 3.3V regulator (LM3940) Xbee RF
module
Slide 42
Battery life test 6V battery pack (robot side) 2100 mAH / 330
mA = 4.45 Hours 9.6V battery pack (robot side) Free run -> 2200
mAH/320 mA = 4.81 hours With 10 lb -> 2200 mAH/1360 mA = 1.13
hours With 20 lb -> 2200 mAh/3360 mA =0.46hours PartCurrent
draws Microcontroller105 mA Motor controller115 mA Ultrasonic
sensor (Rx) 50 mA Xbee RF module (Tx) 55 mA Total330 mA PartCurrent
draws 4 x Gear motor @ free run 80 mA *4 = 320 mA 4 x Gear motor
with 10 lb payload 340 mA *4 = 1360 mA 4 x Gear motor with 20 lb
payload 1090 mA *4 = 3360 mA
Slide 43
Xbee Testing This figure shows how Xbee is programmed to give
us the ID, high and the low for the signal which is shared by the
sender and receiver.
Slide 44
Xbee Testing contd. This figure shows that the Xbee is
communicating successfully.
Slide 45
PI Controller Testing The values of the ultrasound sensors are
printed in the com Components of the PI controller are then printed
Also the direction (left or right) of the turn is printed Finally
the adjusted speed of the motors is printed
Slide 46
Technical Problems while building Knight Gear Inconsistency in
devices Ultrasonic sensors Faulty and burned out sensors Weight
sensor Xbee Antennas