13 : Omni-Directional RobotDesign Review

Ben WolfBrent CorneliusEd CramerJohn GrabnerJames Grabner

Advisor & Client:Dr. Nicola Elia

Introduction

• What is an Omni-Directional Robot– A robot that is able to move any direction in the

X/Y plane without changing it’s orientation. As well as being able to move in a single direction while freely rotating 360⁰

• In 2010, a team designed a new robot platform but did not complete it, our goal is complete the assembly of the robot and implement any missing features

Problem statement:

• Current design needs the following:– Analog I/O board– A working IMU– Battery protection and monitoring

• Other features to be worked on– Operating system– Assembly documentation– Chassis reorganization

Functional Requirements• I/O board:

– Needs to have at least 4 inputs– 12 bit resolution at 1kHz

• IMU:– Assess purchased Pololu CHR-6d– Find alternatives if necessary– IMU must be mounted on robot and functioning

• Operating System:– Must boot in 30 seconds or less– Must be tolerant of unexpected power loss– Must be compatible with existing hardware

Functional Requirements• Chassis:

– Must have outer shell for use with visualization system– Undercarriage wiring must be organized– Use PCBs where possible to simplify manufacture and

assembly of robot

• Battery protection:– Must have automatic disconnect to prevent battery

module damage– Battery voltages must be available to OS/AI

Non-Functional Requirements

• Maintain function of “legacy” system

• Provide documentation for robot assembly

• Characterize robot performance

Design (8 slides)

Operating System

• Korebot series robots used Familiar Linux• The previous team used Ubuntu 10.10 to get

started quickly• A more efficient replacement was needed

– Reduce boot time– Stored on compact flash memory– Read-only file system to prevent corruption and

unintentional modifications

Operating System

• Researched a variety of embedded and portable systems– MicroCore Linux, Linux From Scratch– Emdebian Linux

• We needed a quick start as well– Custom kernel and Debian 6 installed on the robot– Gather information about the hardware– Start testing other components like the I/O board

Analog I/O Board

• PCI boards were too expensive• Inadequate resources to develop our own• Chose WinSystems PCM-MIO-G

– Linux supported out of the box– Less expensive than other models– Software available for testing before purchase

• Issues with Stack Configuration

Battery Protection and Monitoring(BPAM)

• BPAM requirements– Must shut off pack when one or more cells reached 3.2-3 volts– Must be able to report cell voltages over a serial line– Must be able to work with 2 or 3 cell batteries

• We decided to not use commercially available BPAM– Had overvoltage protection, but no under-voltage protection– Only protected a fixed number of cells– Most did not meet all the requirements

• Decided to design and implement our own microcontroller based battery protection system that would shut off power to a robot when cells reached 3.2 volts, be able to be used with 2 or 3 cell battery packs, and would be able to communicate cell voltages over a serial line.

BPAM Schematic

BPAM Design• PIC16F688 microcontroller

– Has 8 channel 10 bit ADC, we need three to read cell voltage– Output pins can be used to turn on/off power MOSFET and

sense amplifier– Has USART for serial communication

• TL084 JFET Quad Op Amp– Input Impedance > 1Tohm– Can drive resistor dividers on sense lines

• MC78LC00 Regulator– Provides the microcontroller with 3V for power– Low quiescent current

Chassis Organization

• System before our additions– Two Layer System– Needs Switches, Indicator Lights, and Top Shell – Lower chassis wiring needs to be redone

Chassis Organization

• When adding I/O board Stack configuration will need to be altered– Computer is PC-104/+ Form factor – Mesa board is PCI-104– I/O is PC-104– Solution:

• Adapter Board

Adapter board

• Pass through PCI Bus• Offset ISA Bus

Adapter Board

• Secondary function – Chassis ReorganizationThe empty board space was not wasted:

• Motor drivers• Voltage regulators• Motor connectors• Motor controller interface• New motor current sense circuits• Switches

IMPLEMENTATIONTESTINGEVALUATION

Operating System

• There are several versions of the OS today:– Development OS (eris-00.04)– Veisha OS (eris-00.03)– Debian Live (generic)

• Fastest boot time is 38 seconds– 18 seconds consumed by POST– CF slot much faster than USB with GRUB

• More robust file systems are necessary– Compressed and/or ramdisk is ideal– Move to journaling file system

I/O Board: Accuracy and Sample Rate

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PCM-MIO-G High Speed Sampling1KHz 9Vpp Sine Input (~56 KHz)

Elapsed Time (uS)

Volts

HP 34401A PCM-MIO-G4.2045 V 4.2027 V8.4119 V 8.4117 V2.6406 V 2.6401 V

•A simple how-to program was written for future users

• Maximum observed sample rate was 71,428 Hz

I/O Board: Sensor Manager

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Sensor Manager Data Logging200Hz sinusoidal input

Time (ms)

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Sensor Manager Data Logging200Hz sinusoidal Input (~2300Hz)

Sample #

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BPAM• gEDA used to create schematics and PCB

layout– Considerations for making PCB by ourselves

• Microcontroller Programming – MPLAB IDE v8.76 with Hi Tech C Compiler– PICkit 2– Main Functions of the Program

BPAM Pictures

BPAM Testing

• Microcontroller Functionality• Linearity and Accuracy • Static Load Test• Complex Load Test• Testing with a Robot

Chassis Reorganization

• Power Switches• Bumper Guards• Adapter Board

Adapter board

• gEDA was once again used to create schematics and PCB layout

• Schematic to PCB tool • Board was ordered through Advanced Circuits

– Assembly is nearly complete, connectors arriving later today

Adapter Board Pictures

Conclusion

• BPAM – Primary Goal Accomplished (batteries are

protected)– Do not foresee any major obstacles to complete

remaining requirements• Operating System

– Boots quickly and is in a usable state

Conclusion

• I/O Board– Integrated on robot and performs adequately

• Chassis Successfully reorganized– Requires a permanent lid assembly

Lessons Learned

• Just because it seems simple doesn’t mean that it will be done quickly (BPAM)

• The best robot is useless without proper documentation

• Don’t let a project intimidate you, start working and ask for help if you get stuck

Questions