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Group 6 Rene A. Gajardo Do Kim Jorge L. Morales Siddharth Padhi

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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.

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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

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Specifications ComponentDesign Specification Chassis 1.5 in above ground Length = 19.5in Width = 15.5in Height (max) = 21.75in Height (min) 12in Ultrasound Detection3m Battery Life2 hours Battery Charge Rate1.5 hours (electrically) Wireless Connectivity Range400 feet

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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.

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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

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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

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Pin connections of Mega Pro 3.3

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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.

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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

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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

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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.

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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

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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

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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

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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.

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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

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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

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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%.

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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.

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Wheels Configuration Mechanisms to provide locomotion that is required for the Knight Gear Differential Drive Ackerman Drive Synchronous Drive, and Omnidirectional Drive

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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

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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

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Chassis contd

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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.

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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

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Class Diagram of Knight Gears Control Algorithm

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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.

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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.

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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:

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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.

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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

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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

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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

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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)

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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

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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

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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.

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Xbee Testing contd. This figure shows that the Xbee is communicating successfully.

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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

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Technical Problems while building Knight Gear Inconsistency in devices Ultrasonic sensors Faulty and burned out sensors Weight sensor Xbee Antennas

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