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

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.

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

Specifications

Component

Chassis Ultrasound Detection Battery Life Battery Charge Rate Wireless Connectivity Range

Design Specification

1.5 in above ground Length = 19.5in

Width = 15.5in

Height (max) = 21.75in

Height (min) – 12in 3m 2 hours 1.5 hours (electrically) 400 feet

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.

Micro Controller Comparison

Digital I/O Analog I/O Operating Voltage Cost MC68332

15 15

Intel 8051 PIC 18F452 Atmega 2560

24 8 24 8 54 16 5V $11.94

3.3V

$1.50

5.5V

$4.68

3.3V

$17.98

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

 Pin connections of Mega Pro 3.3

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.

Products Resolution Reading Rate Maximum Range Required Voltage Required Current Operational Temperature Price XL MaxSonar -EZ XL MaxSonar -AE LV MaxSonar -EZ HRLV MaxSonar -EZ Parallax PING))) 28015

1cm 1 cm 1 cm 1 mm 1 cm 10Hz 10Hz 20Hz 10Hz 10Hz 300in-420in 300in-420in 254in 195in 118in 3.5V-5.5V

3.5V-5.5V

2.5V-5.5V

2.5V-5.5V

5 V 3.4mA

3.4mA

2.0mA

3.1mA

30mA 0C – 65C - 40C – 70C 0C – 65C 0C – 70C $27.95

$29.95

$21.95

$28.95

$29.99

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

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.

Zigbee

 Low cost, low power, wireless mesh network.  The following are the parameters of Zigbee

Parameters

Range Operating Frequency Complexity Power Consumption

ZigBee

10-100 meters 2.4 GHz Low Low

Zigbee contd…

 Zigbee comes in 2 series. The following is the comparison table between Series 1 and Series 2:

Parameters Range Power Consumption Frequency Data Rate Cost XBee Series 1

300 ft.

50mA @ 3.3v

2.4 GHz 250 kps $22.95

XBee Series 2

400 ft.

40mA @ 3.3v

2.4GHz

250 kps $20.95

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

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.

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

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

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%.

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.

Wheels Configuration

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

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

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

Parameters

Length Width Height (max) Height (min)

Measurements

19.5 in 15.5 in 21.75 in 12 in

Chassis contd…

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.

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

 Class Diagram of Knight Gear’s Control Algorithm

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.

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.

Motors cont…

Spur DC geared motors (x4)  DC motor combined with a gearbox that work to decrease the motor’s speed but increase the torque  Pololu’s metal gear motor: Operating voltage Free speed Current stall current Torque 6V 120 RPM 80mA @ free run 2A 9.6 lb*cm

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.

0 1

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

Model Brand Operating supply voltages Tolerant peak output currents Continuous currents per each channel H-Bridges Control method Internal diodes Price (from mouser electronic website) L293D

Texas Instrument/ Stmicroelectrics

SN754410

Texas Instrument 4.5V ~ 36V 1.2A

600mA Quadruple-Half PWM YES $1.12 4.5V ~ 36V 2A 1.1A

Quadruple-Half PWM YES $0.87

DRV8833

Texas Instrument 2.7V ~ 10.8V

I 2 1A 500mA Dual C / PWM YES $2.58

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

Power source Rechargeable battery selection

Voltage Capacity load Recharge Cycle Charging Time Discharge Efficiency Operating Temperature Self Discharge Rate

NiCad

1.25

Low 1000 1 - 1.5 hours 70 – 90 % -20 – 45 C 10%

NiMH

1.25

High 500 - 1000 2 -4 hours 66 % -20 – 45 C 25%

Alkaline

1.50

High 10 - 50 2 – 3 hours Varied by Capacity Load -20 – 60 C <2%

Li-ion

3.6

High 300 – 1000 2 – 4 hours 80 – 90 0 – 45 C 8% at 20C 15% at 40C 30% at 60C

Why Nickel Metal Hydride ?

 High capacity  Environmentally friendly  NiMH batteries can be charged at any time without affecting battery life  Cost effective

Power System

 Motors draw too much of currents !

 Separate power source for motors (9.6V 2200 mAH)  6V 2100 mAH battery pack is used for other electronic devices  Power Regulation required for other devices  Power dissipation of other electronic devices  (6V– 5V) * 330mA = 0.33W

 (5V-3.3V)*55mA = 0.094W

 Low dropout linear voltage regulators are used.

Linear Voltage Regulators

LM2940

 LM2940 LDO regulator for 6V to 5V @ I o =1A

LM3940

 LM3940 LDO voltage regulator for 5V to 3.3V@ I o =1A

Power system power regulation cont.

 Block diagram of power system 6V -> 5V LDO regulator (LM2940) 6V 2100mAH battery pack Switch 5V -> 3.3V LDO regulator (LM3940) 9.6V 2200mAH battery pack Microcontr oller Motor driver IC Ultrasonic sensors Xbee RF module (wireless antenna) DC geared Motors

Power system power regulation cont.

 Block diagram of power system cont.

6V 2100 mAH battery pack Switch 6V ->5V regulator (LM2940) 5V -> 3.3V regulator (LM3940) Ultrasonic sensor Xbee RF module

Battery life test

 6V battery pack (robot side)  9.6V battery pack (robot side) Part Microcontroller Current draws 105 mA Motor controller 115 mA Ultrasonic sensor (Rx) Xbee RF module (Tx) Total 50 mA 55 mA 330 mA  2100 mAH / 330 mA = 4.45 Hours     Part 4 x Gear motor @ free run 4 x Gear motor with 10 lb payload 4 x Gear motor with 20 lb payload Current draws 80 mA *4 = 320 mA 340 mA *4 = 1360 mA 1090 mA *4 = 3360 mA 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

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.

Xbee Testing contd….

 This figure shows that the Xbee is communicating successfully.

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

Technical Problems while building Knight Gear

 Inconsistency in devices  Ultrasonic sensors  Faulty and burned out sensors  Weight sensor  Xbee Antennas