Modularity for a Robotic Locomotion System Kenneth Chin and Prang Chim January 26, 2001 Advisor: Dr. Jim Ostrowski

Case Study Approach Early Stages System & Design Analysis Future Perspective An exploration into the overall goal of our project where modularity is defined providing an overview into the mechanical structures and communication architecture. A detailed examination of the mechanical, electrical, and communication components of the electro-mechanical system. A hindsight perspective of problems encountered while elaborating on improvements for the process while providing an outlook upon the project’s future.

The Early Stages Overall Goal Modularity? Architecture Overview What is the point of this project? What is modularity?. An overview of the system architecture from a high level in order to understand the integration with lower level components.

Overall Goal Investigation of modularity Design of a component to act as a universal interface between the base unit and components Improved wheel modular unit and base Implementation of an efficient bus system with expansion capabilities with hardware

What is Modularity? Modular/ Modularity (adjective) “Designed with standardized units or dimensions, as for easy assembly and repair or flexible arrangement and use.” Application to Robotics Easily attachable and detachable modules Each module contains the necessary mechanical and electrical components (I.e. motors, microprocessors, etc.)

Architecture Overview Master Processor Slave Processor Slave Processor Slave Processor Slave Processor FT Chip Servo Motor 1 Servo Motor 2 Consists of single master processor where all program instructions originate. Independent slave processor allow for device independent calibrations. Instructions passed from master- >slave->FT639 (drives servo motors directly) Exploded View

System and Design Analysis Mechanical Design Electrical System Communication Controls An exploration of the mechanical design of: body, universal insert module, and servo motor housing. An exploration of PCB design, master module, and the slave module. An explanation of the communication of the overall integration system.

Design Criteria DimensionExplanation Size Small and compact to keep weight to a minimal Weight Lightweight allows for decreased torque requirements on motors while allowing for increased mobility Functionality Ability to be functional pliable and adaptable Possibility to incorporate sensors Mobility in terms of a wheel and with legs

Body Design Design 2Design 1 Components made entirely of plexiglass each side is one single piece Problems heavy a lot of manufacturing Components made entirely of plexiglass sides are individual pieces Problems slightly lighter many parts

Body Design Components 2 sheets of 6x10x0.25” plexiglass – Manufactured using CNC machine 12 Aluminum threaded Round Standoffs: ¼” OD, 1-1/2” length Advantages Light weight less manufacturing (standoffs are off the shelf products a total of 8 slots for modules Final Design

Universal Insert Module Initial Design: Two part component

Universal Insert Module Final Conception One piece component made of ABS material. Easily manufactured with the use of the FDM machine.

Servo Motor Housing Problem Resulting moments on servo horns Deformation of servo horns Original Design

Servo Motor Housing Lower Servo Unit (Driving)Upper Servo Unit (Steering) Solution Redirect moment onto a shaft made of stronger material shafts connected to servo motors with use of gears and chains 6-32 set screws connects to insert module Steering Shaft Steering Shaft connection Driving Shaft Ball Bearing slot 6-32 set screws set steering shaft to lower unit

Assembled Module Insert Module made of ABS manufactured using FDM machine Upper servo unit made of ABS 1.25x3x1’’ manufactured using CNC machine Lower servo unit made of ABS 1.25x3x1’’ manufactured using CNC machine Shafts Drill Rods Shafts from toy car Servo Motors Wheel taken from toy car Spacers 4 pieces ¼” OD, 1/8” lenght

Final Assembly Complete assembly of robot with four wheel modules inserted into the body

Master Module Basic Stamp II Micro- controller Dedicated Bus System for SEND Dedicated Bus System for RECEIVE 2 individual bus systems for sending and receiving data to avoid data collisions Primary Program sequence contained within InputsOutputs Power Source: provides power to the micro- controller and also to the slave modules for their respective micro- controllers. Data Line Out: Utilizes a serial line sending data and individual instructions to each slave module component (i.e. such as speed, position) containing a micro- controller Data Line In: consists of a single serial line coming from each individual slave module carrying valuable data instructions from each slave (i.e. may include speed, position, error, and feedback information)

Slave Module Schematic Each slave module unit is independent unit containing: FT639 servo controller chip, 1 Basic Stamp II microcontroller 2 dedicated 5V lines (servo motors & chips) 180 degree and 360 degree servo motor on board Courtesy of Kapil and Darnel Each slave module unit is independent unit containing: FT639 servo controller chip, 1 Basic Stamp II microcontroller 2 dedicated 5V lines (servo motors & chips) Pin 0 Pin 14 Pin 15 Microcontroller Pin Assignments Dedicated SEND line to master Dedicated RECEIVE line to master Dedicated COM to FT639 chip

PCB Circuit Board Generated circuit board to be inserted into each module unit to allow for processing on the slave as opposed to master Generated custom-designed PCB schematic sending NC and drill files for production 2 layers: Top layer (red) and Bottom layer (blue) Servo Power RCV Line System Ground SND Line Future Expansion System Power 3 dedicated channels for power and ground 2 dedicated I/O channels for communication with the master 2 dedicated channels for future expansion (hardware id sequence)

Communication Controls Master Module Unit Slave Module Unit (Addressed at $FF) ($FD) …….. ($FF) …….. Addressing ($FC, $FD, $FE, $FF) Allows for routing of information from master to appropriate slave unit Sends data serially at 2400 baud Allows handshaking while slave constantly pings for incoming data AddressPositionServoAddress Completion Checks to see which modules are plugged in routing data and adjusting program accordingly Flow Sequence Master -> Slave > FT chip -> Slave -> Master

Future Perspective Results & Review Continuation Credits What were the results of our projects? What problems did we encounter through the project? Who we would like to thank for making this project a success. An insight into the next generation model.

Problems Encountered Problem: Inability to align parts consistently on the CNC machine. Result: Not using the bearings for the wheel shaft Manufacturing Problem: Inability to produce high quality and tolerant parts through fusion deposition modeling (FDM).. Result: Loss tolerances upon inserting screws with high accuracy. Problem: Gear Specifications and slippage Result: Utilized two set screws and drilled into shafts but reduced torque Mechanically Problem: Turning Mechanism for the wheel module unit Result: Moment still exists but is greatly reduced with spacer

Problems Encountered Problem: Data loss and Collisions Result: Consolidated send and receive lines on individual bus systems and utilized improved power supply Electrically Problem: Data transmission Speeds Result: Utilized a 2400 baud transfer rates due to limitations imposed by the FT639 chip even though optimal transfer rate between Basic Stamps was found to be 9600 baud. Problem: Faulty Connectors/ connections Result: Reconnecting slave unit several times until communication link established. Investigate better quality connectors. Problem: Sending data from master to slaves several times before communication sequence established Result: Integrated system works at times. Problem currently under further investigation.

The Next Generation Model Solutions to Gear Slippage use of metal gears to prevent stripping from screws the use of larger gears to provide a better contact for the set screws modifications to servo motor housing to incorporate a larger diameter size shaft Speed control with the use of encoders Hardware ID tags determine location of module that is plugged in relative to the body Use of a multiplexer to control data flow Allows for more uniform integration with the software tagging Implementation of a Feedback System Implementing proximity and various other sensors to create a “smart system” creating a feedback loop

Credits Bob Miller, Wally Szczesniak, Terry Kientz, Brett Balogh, Siddharth Deliwala, John Bowen, Darnel Degand, Kapil Kedia, Adrian Fox, Christopher Li, and of course our advisor … Dr. Jim Ostrowski