PowerBotGroup #2:Tarik Ait El FkihLuke CremeriusMarcel MichaelJerald Slatko

Sponsored By: Aeronix, Inc.

Project Description

Autonomous robot purposed to provide supplemental power to mobile devices (laptops, mobile phones, etc.).

Uses onboard navigation algorithms to navigate to user’s location.

Incorporates an iOS application to provide robot statistics and manual control.

Project Motivation

Battery life longevity in mobile devices is a constant issue.

Wanted to create a charging solution that could charge the device without inconveniencing the user.

The device would be simple to use, allowing for easy adoption into a users everyday routine.

Objectives

PowerBot should be able to navigate autonomously to a user’s location.

PowerBot should be able to be remotely controlled by the user through the use of an onboard camera and the provided iOS application.

PowerBot will contain a battery used to charge external devices through the use of inductive and USB interfaces.

Specifications

Will be at most 36” long

Max speed of 5 mph

Battery life of minimum 24 hours

Ability to provide charge to mobile devices 100% of the time.

Switching Voltage Regulators

Needed to regulate power to the different systems in PowerBot.

Highly efficient when compared to linear voltage regulators; 14-40% vs. 85-90%.

Inductive Charging

9 V switching regulator: LT1424-9

Used to step down voltage for charging mat.

SO-8 package.

Charging mat offers a degree of flexibility due to lack of wires.

Inductive cases are needed unless implemented (Qi) by manufacturer.

USB Charging

5 V switching regulator: DE-SW050

Used to step down voltage for USB charging.

Pin-compatible with 78XX family (TO-220 package) of linear voltage regulators.

USB, although wired, is, well, universal.

Microcontroller Supply

3 V switching regulator: DE-SW033

Used to step down voltage for the microcontrollers.

Pin-compatible with 78XX family (TO-220 package) of linear voltage regulators.

Motors

Stepper Motor:To be used to rotate (Θ-axis) the solar panel.

Brushed DC Motor:To be used to drive the rear wheels.

Motor SpecificationsPart Number SST58D3830 RS-540

Manufacturer Shinano Kenshi

Tamiya

Type Stepper DC Brushed

Step Angle (°) 1.8 N/A

No Load RPM N/A 16,800

Voltage (V) 2.1 4.5-12

Current (A/Phase) 3.0 1 (no load)

Resistance (Ω/Phase) 0.7 N/A

Inductance (mH/Phase) 1.3 N/A

Holding/Stall Torque (kg-cm)

7.3 2.84

Rotor Inertia (g-cm3) 290 N/A

Weight (kg) 0.71 0.153

Dimension (L) 54 mm 50 mm

Motor Controllers

MSP430F123 will be used to control the solar panel [stepper] motor.

Contains hardware UART for serial communications.

Motor Controllers

MSP430F2616 will be used to control the DC brushed motor.

Its features: Interfaces with UART. 16 MHz with 4 kB of RAM

and 92 kB of flash memory.

48 GPIOs. ADC resolution of 12 bits

with 8 channels.

R/C Car Chassis

Somewhat standard over-the-counter licensed R/C car.

Large wheels allow for maneuverability.

Chassis Modifications

Swap out the drive motor to (DC Brushed).

Remove the [red] plastic body frame and create a foundation for PowerBot.

Obstacle Avoidance Obstacles will be detected using ultrasonic ranging

sensors

As PowerBot moves, the ultrasonic sensors rapidly take readings to gather range data in real time.

The obstacle avoidance algorithm will maneuver PowerBot in response to the presence of obstacles.

Three modes of operation: Active Adjustment (AA) Reverse-Reset (RR) Off

Obstacle avoidance is OFF by default. It must be enabled by the iPhone user

Modes of OperationActive Adjustment (AA)

Primary mode of operation

Front two ultrasonic sensors are active

A range reading within the AA minimum distance causes PowerBot to steer either left or right to avoid it.

PowerBot will attempt to re-align

Ultrasonic SensorsLV-MaxSonar® – EZ0™

Operates at 2.5 V – 5.5 V

Avg. current draw: 2 mA

Min. Distance: 6 in. Obstacles closer than 6 in. give

reading of 6 in.

Max. Distance: 254 in. (21 ft.)

1 inch Resolution

Range readings can be taken at about 20 Hz, every 50 ms.

Output modes include: Analog

Pulse Width

UART (not quite RS-232)

Image Credit: www.maxbotix.com

PIC32 Microcontroller

PIC32 family of microcontrollers was chosen to drive PowerBots navigation and Wi-Fi communication functions.

The PIC32 features an 80 MHz clock with onboard 512 kB of flash and 128 kB of RAM.

Model Number: PIC32MX695F512H

Wi-Fi Communication• Used as the primary mode of communication between PowerBot

and the iOS application.

• 802.11 Wi-Fi used as a physical layer with TCP sockets used for higher level communication.

Application Layer

MCU – Serial

802.11 – Socket

iOS – Serial

802.11 – Socket

Application Layer

Embedded Software

iOS Software

Wi-Fi Module: MRF24WB0MA

• The MRF24WB0MA microchip provides a complete Wi-Fi solution for onboard communication with PowerBot.

• The Microchip TCP/IP stack works with the MRF24WB0MA and allows for easier implementation of sockets and the passing of data via TCP.

PIC32 Wi-Fi Circuit Board

Microchip Wi-Fi Comm Development Board was used for prototyping.

Custom circuit board was based off of this design.

Combines PIC32 MCU with the MRF24WB0MA Wi-Fi module.

Additionally gives access to 4 UART ports, as well as 6 GPIO pins used for ultrasonic sensor data acquisition and motor commands

PIC32 Wi-Fi Circuit Board

PIC32 Wi-Fi Board Layout

iOS Application

Obstacle AvoidanceAlgorithm

Motor Control

Power Manageme

nt

PowerBot

Sonar Sensors

Stepper Motor

Solar PanelCharging

Ports

Software Layout

iOS Application

Written in Objective-C using Xcode 4.4.

Provides users access to:

Manual mode Obstacle AvoidanceUltrasonic sensor status

Manual Control

Gives the user manual controls to drive PowerBot.

Sensor icons blink when currently taking distance readings.

Status of Wi-Fi connection shown above robot controls.

System Status

Shows the user the current sensor status of PowerBot.

Displays the onboard sensor distance readings

Shows the number of readings received from each sensor

I/O Data button allows viewing all incoming TCP data

System Settings

Allows the user to open a socket connection to PowerBot once the user has joined the ad-hoc network PowerBot broadcasts.

Toggle button for turning obstacle avoidance on or off.

Power

Battery Requirements

24 V battery

At least 2 Ah

Deep cycle for increased usage time

Low internal resistance

Flat discharge rate

Lightweight

SPECIFICATIONS Ni-Cd Ni-MH Li-ion Li-Po

Energy Density (W·hr/kg) 40–60 70-90 100-160 130-200

Capacity (Amp-hr) 1 2.4 2.8 2.6

Internal Resistance (mΩ) 100-200 200-300 100-200 200-300

Nominal Voltage (V) 1.2 1.2 3.6 3.7

Discharge Rate Flat Flat Flat Flat

Recharge Life 500-700 cycles 600-1000 >600 >1000

Disposal Must be recycled Recyclable Recyclable Recyclable

Charge/Discharge Efficiency

70-90 % 66 % 80-90 % 99.80 %

Cost ($/Whr) 2 2.75 2.5 2.8-5

Battery Choice

Lithium Polymer Battery

Polymer Li-Ion Battery

18650 cell type14.8 V (working)16.8 V (peak)2.2 Ah 32.56 Wh

Reasons for choosing:• High energy density (Wh/kg)• High energy/dollar (Wh/$)

Alternative Power Source

Power outlet:“Unlimited” powerQuick charging of the battery

Solar panel:Environmental ImpactFinancial BenefitsEnergy Independence

Solar Panels Specifications

Monocrystalline Polycrystalline Thin film

Power 10 W 10 W 10 W

Open Circuit voltage 21.5 21.4 24.2

Short Circuit Current 0.64 0.68 0.84

Maximum Power Voltage 17.5 16.8 17.3

Maximum Power Current 0.57 0.6 0.64

Efficiency 15 % 12.5 % 6.3 %

Cost/W 10-11 8.5-9.5 10

Solar Power Selection Details

Solar Panel Type Monocrystalline

Manufacturer INSTAPARK

Efficiency 15 %

Power 10 W

Maximum Voltage Power 17.5

Maximum Current Power 0.57 A

Open Circuit Voltage 21.95 V

Cost $39.95

Output Efficiency

Increasing the output efficiency of the panel:

Increase panel size

Implement tracking system

Single axis

Dual axis

Single Axis Control System

Ambient Light

Photoresistor

MSP430 Longitude Orientation

Dual Axis Control System

Ambient Light

Photoresistor MSP430

Latitude Orientation

Longitude Orientation

Compare and Contrast

Dual axis control system would require more maintenance.

There’s an extra cost involved in utilizing an extra motor or actuator.

Increased complexity.

6% extra efficiency compared to a single axis control system; not worth it.

Solar Panel Implementation

Free rotation of theta ( angle.

Phi ( is fixed in single axis system.

Optimal angle of phi ( is 15°.

BudgetPart Cost Quantity Total Cost

RC Car Chassis

$50 1 $50

Motors

Solar Panel $40 1 $40

Inductive Charger

$40 1 $40

Battery $105 2 $210

Dev Board $50 1 $50

PICKit 3 $50 1 $50

Sonar Sensors

$30 10 $300

Circuit Component

s

Total ~$550

Distribution of Labor

Tarik

Luke

Marcel

Jerald

Solar Panel 80% 5% 10% 5%

MCU Software 25% 25% 25% 25%

Robot Construction

10% 5% 80% 5%

Wireless Design 5% 70% 5% 20%

Navigation/AI 5% 20% 5% 70%

Concerns

Ability to accurately depict a global map and link it to PowerBot’s local map.

Ability to correctly implement EERUF.

Ability for PowerBot to become unstuck in a trap situation.

Questions?