Collisionless Rimless Wheel (Wired) P13211
Week 9 Detailed Design Review
Meeting Purpose
1. Review project details and engineering “numbers”
2. Review of energy calculations
3. Review of all part analyses
3. Review of Bill of Materials
Review Topics
1. Project description
2. System structure
3. Energy Calculations
4. Chosen Design
5. Chosen Materials
6. Bill of Materials
Meeting Date: November 2nd, 2012
Meeting Time: 12 noon - 2:00pm
Meeting Location: 09-2130
Proposed Agenda:
Start Time / Topic / Required Attendees12:00 / Project description, goals, and deliverables / Dr. Gomes, Dr. Slack, Dr. Hanzlik
12:10 / System Structure / Dr. Gomes, Dr. Slack, Dr. Hanzlik
12:20 / Energy Calculations / Dr. Gomes, Dr. Slack, Dr. Hanzlik
12:40 / Chosen Design / Dr. Gomes, Dr. Slack, Dr. Hanzlik
1:05 / Chosen Materials / Dr. Gomes, Dr. Slack, Dr. Hanzlik
1:25 / Bill of Materials / Dr. Gomes, Dr. Slack, Dr. Hanzlik
1:45 / Questions/Clarifications / Dr. Gomes, Dr. Slack, Dr. Hanzlik
Team Members
Name / RoleOwen Accas / Mechanical Engineer
Daniel Crossen / Mechanical Engineer
Madeline Liccione / Electrical Engineer
Rebecca Irwin / Electrical Engineer
Hao Shi / Mechanical Engineer
Project Motivation & Background
As robots become more and more integrated into our daily lives, the energy consumption has become a critical issue for robotic design. Energy efficiency for robotic walkers has garnered much research attention from the robotics community. Cost of transport (CoT) is usually used as a measure for locomotion energy efficiency, and is defined as energy used/(weight moved x distance travelled). The rimless wheel is very promising as a candidate for low cost-of-transport robotic transportation. Previous research efforts at RIT’s Department of Mechanical Engineering have led to a prototype rimless wheel that can walk down an 8 degree incline without an external power source.
Project Statement
The goal is to design, build, and test a rimless wheel that is capable of walking at least 25 steps across level ground with minimal energy consumption while collecting data of the dynamics of the motion.
Objectives
1. Design and build a rimless wheel that can walk at least 25 steps across level ground
2. Achieve at least 40 trials with 25 steps per trial
3. Record and analyze relevant dynamical variables as functions of time
4. Record and archive videos of successful trials
5. Achieve CoT of 0.1 or less
Deliverables
1. A rimless wheel that can walk at least 25 steps across level ground
2. Data collected on the angular motion and position of the inertia wheel and rimless wheel
3. Videos of successful trials
4. User manual
Assumptions & Constraints
1. Assume all materials we choose are available to us (will investigate post SDR)
2. Assume lead times for custom parts will be less than the length of MSD II (will investigate post SDR)
3. Size, weight, and exotic materials must be constrained
4. Power usage should be constrained
5. Cost should be less than $900, ideally less than $800
Issues & Risks
1. Material lead times and manufacturability
2. Material flaws
3. Effectiveness of actuation
4. Technical errors
Expectations for Detailed Design Review
1. Assessment of the feasibility of our proposed system
2. Mutual understanding between the customer, the project guides, and the team about the objectives and deliverables of the project
3. Obtain critical feedback on our performance as of this review
Customer Needs
While the PRP gave an initial list of 9 customer needs, we scheduled a meeting with Dr. Gomes in order to get a better list, and to hear exactly what he wanted, with no solutions attached. We came up with the following list of 11 customer needs:
Customer Needs Number / Importance / DetailCN1 / 1 / Collect data to prove periodic motion across level ground
CN2 / 2 / Collect current/voltage of battery
CN3 / 1 / Record angular velocity of the spokes and wheel (theta_dot)
CN4 / 1 / Record angle between the two (theta_relative)
CN5 / 2 / Record current/voltage to actuators
CN6 / 1 / Have periodic motion
CN7 / 1 / 25 steps ('infinite' walking distance)
CN8 / 2 / Resolution needs: aim for 100 Hz
CN9 / 1 / Reduce energy loss (both electrical and mechanical)
CN10 / 1 / Be portable
CN11 / 1 / Aiming for .05 or .1 Cost of Transport
CN12 / 2 / Be rigid
Engineering Specification
Function / Specifications (metric) / Unit of Measure / Marginal Value / Ideal Value / Customer Needs Satisfied / OwnerS1 / System / Largest dimensions / m / ≤ 1.5 / ≤ unpowered prototype / CN10 / Owen
S2 / System / Weight / Lbs / ≤ 20 / ≤ 5 / CN9, CN10 / All
S3 / System / System cost / $ / < 900 / < 800 / CN9 / All
S4 / System / Number of steps / Integer / ≥ 20 / >=25 / CN6, CN7 / Maddie
S5 / System / Resolution of angular velocity data / deg/sec / 1 / ≥ 0.1 / CN1, CN3, CN8 / Becky
S6 / System / Resolution of angular position data / deg/sec / 0.5 / ≥ 0.1 / CN1, CN4, CN8 / Becky
S7 / System / Total cost of transport of device / Unitless / 0.1 / 0.01 / CN9, CN10, CN11, CN12 / All
S8 / System / Data sampling rate / Hz / ≥ 100 / ≥ 500 / CN1, CN2, CN3, CN4, CN5, CN8 / Maddie
S9 / System / Operational time between charges for system / Hours / 0.5 / 1.5 / CN9 / Becky
S10 / System / Amount of data for onboard storage / Hours / 0.1 / 0.5 / CN1, CN2, CN3, CN4, CN5 / Maddie
S11 / System / Safe for user and observers / Binary / Yes / Yes / CN12 / All
S22 / System / Number of 25 step trials achieved / Integer / ≥ 40 / ≥ 50 / CN6, CN7 / All
S23 / System / Training time (1st time) / Hrs / 0 / <0.5 / CN1 / All
Proposed Design
1. Frame material
● Carbon fiber plates
● Thin walled steel braces
● aluminum axle
2. Number of spokes/points of contact per side
● Decided on 5 for ease of comparison with current prototype
● 4 seemed like the most challenging/desirable number, but analyses done by previous students indicates that the amount of force needed to actuate the system may be too large to surmount
3. Actuation Mechanism
● String drive (strings wrapped around motor)
● Rotating axle rigidly connected to the bike wheel
4. Data Processing and Control
● TI microprocessor + custom controls work
○ Complete control over motor control system; best way to ensure optimal power consumption
○ May be too difficult and time-consuming to program and configure from scratch
● TI modular motor control kit
○ Will not have to program a microcontroller from scratch
○ Can simply plug in a microcontroller card; all of the motor driving and problems (back emf, optical isolation, etc.) are taken care of
○ Different kits for different types of motors
○ Biggest drawbacks are large size, nonuniformly distributed mass and high cost
● Gyrosensors are most viable option for relative angle and angular velocity measuring
5. Slippage Reduction
● High friction feet (using PC non-slip pads)
Detailed Block Diagram
Proposed Design CAD Drawing Description
● 2, pentagon-shaped carbon fiber plates
● 5 Thin-walled steel supports at the ends of each of the points
● Aluminum mounting plates to mount the axle to the fiber glass plates
● similar string/spring set up as prototype, but the string is now attached to motors inside the axle
● 2-part axle: smaller diameter axle to hold the bike wheel bearing-connected to the larger one to hold the motor
● motor inside the axle on one side of the bike wheel, meant to add torque to the bike wheel through the axle, which is connected to the frame by bearings
● batteries mounted on outside of bike wheel for increased inertia (modeled currently as 9V batteries, but will most likely go with a better alternative)
● all connections between plates will be hollow for installing wires, excluding the middle axle
● We will be adding high friction feet/pads onto the end of each of the points
Increased surface area provided by plates gives more area for electronics (electronics currently not modeled on cad drawing
● Plastic Inserts inside foam so as to not crush the foam when tightening fasteners
Proposed Design CAD Drawings
Proposed Design Schematics and Component Specific Block Diagrams
Custom schematics are still being finalized and will be presented at the time of the review.
Closed loop with feedback sensor motor control system that is the basis for each control system. The feedback sensor will likely be an encoder packaged with the motor.
TI LaunchPad Microcontroller Development Platform, Page 1
TI LaunchPad Microcontroller Development Platform, Page 2
Block diagram of internal workings of L3GD20 3-axis gyroscope
Very basic motion control algorithm not including the clutch system
Bill of Materials (previous design)
Already ordered/Already have obtained
Ready to order/Know where we are ordering from
Do not know where we are ordering from/Do not know what we need (not good condition)
Bill of Materials (new design)
Already ordered/Already have obtained
Ready to order/Know where we are ordering from
Do not know where we are ordering from/Do not know what we need (not good condition)
(Hand out will be provided with larger font)