Week 7 Engineering Review - PowerPoint Presentation

Week 7 Engineering Review Owen Accas - Dan Crossen - Rebecca Irwin - Madeline Liccione - Hao Shi

Detailed Block Diagram

Energy Flow Graph

Double Stance       Time Propagator (RK 4)    

Single Stance   a o    

Current Prototype v.s . Proposed System Simulation Comparison   Current Prototype Parameters Proposed System Parameters   Units of Parameter Number of spokes55QuantityLength of legs0.40640.41656mMass per spoke0.737 0.827 KgInertia per spoke0.0210.0205Kg·m2Mass of inertia wheel0.91081.25KgInertia of inertia wheel0.0723 0.1161288 Kg·m2k-value of spring 37 N·m/rad

10mm diameter aluminum Assume no tension/compression or insignificant tension/compression Shear modulus = 26 GPa Area = Pi*(.01m)^2=pi*10^-4 m^2 Shear failure at ~204 million Newtons which is approximately 45.8 million lbsThis strength will more than account for the forces seen on the axle in shearAxle

Worst case: 1 plate rigid, 1 side has full torque Full torque = (40 lbs /spring)*(2 springs)*1.5 in =120 in- lbs Bending force on each brace =(120 in-lbs)/(14 inches)/(5 braces) =1.714 lbs/brace, therefore assume 2.5 lbs with a safety factorBraces

Shear Strength = 10,500 PSIWith 100 pounds, we would need a cross sectional area of .00952 in^2 or greater to avoid failure With 2.5 lbs (calculated on previous slide), we would see no failure at all, as the pvc we are using has an area of .256 in^2 These will ad .172 kg to entire frame, but add .0217 kg-m^2 of inertia (about 20% increase) Choosing Braces

Plate Selection (Core) The core material we intend to use is Core-Cell Foam, a boat building and repair supply Relatively inexpensive Very strong Readily attainable Thin Low density

Plate Selection (Core) Balsa wood is also a popular core material for composites applications Deemed to be more expensive Not as strong Similarly thin Higher density than Core-cell

Plate Selection (Composite) SAE Boeing Carbon fiber is our selected coat Incredibly strong, especially in tension and compression (along the weave) Very thin Very consistent Aesthetically pleasing Would be expensive (~34.99 per 50” x 30”) We have a free connection to needed amount

Plate Selection (Composite) Fiberglass was another option for our top coat Less expensive than carbon, if we had to buy Not quite as strong Most fiber weaves are more random Similar material properties, carbon is free

2 Gyroscopes (L3GD20) – 3.3 V @ 7 mA = .0462 W 1 Encoder (E5)– 5 V @ 50 mA = .25 W Current Sensor (ACS714) – .000012 V @ 10 mA = ~negligible Microcontroller = 0.246mW Total Power = 0.307W Power Consumption of Electronics

Requested Specs: <.5 Deg/Sec accuracy (doesn't make sense, since we will go through about 360 Deg in a second) E5 Encoder: 1024 CpR=.35 Deg sensitivity E5 Encoder: 292.9 RPS maximum (300KHz max count frequency) Encoder

Requested Specs: <.1 Deg/Sec accuracy    L3GD20: +/- 500 Deg/Sec and 400kHz sampling means resolution of .00125 deg This is the same Gyro as is currently used in the prototype Gyroscope

Using NiMH batteries for safety and for voltage matching (1.2V steps), as well as cost (<$3 per battery), ease of replacement, and rechargeablity. Batteries

No specific specs provided Sampling rate of 500 Hz depends upon processor Using error of 2% as spec Current and Voltage Sensors

14.8 V @ 4.1 AmpsIf this motor were on all the time, we would be looking at 61 W, and a cost of transport of approximately 3.36, way over our goal. Therefore, we would like to estimate the CoT when our motor is only on for 1/10 th of a second CoT = .358 Motor (part 1)

There are certain ways to obtain our goal of .05 CoT We looked at getting a larger motor (increased performance & weight). This decreases the amount of time the motor must be active (1/40 th of a second) and increases the denominator of CoT equation. Can rotate ¼ turn in .00625, but we are accounting for negating torque so we assume . 02 seconds (max of 2500 RPMs)CoT = (90 W*(.02 s)+.5)/(51 N*.5 m)= .9Motor (part 2)

Fasteners

Microprocessor Selection

Part name Quantity Cost/item ($/item) Total cost ($) Obtained Lead Times (estimated) Frame plate foam 1 – 44in x 88 in x 9.5 mm $77 $77 Buy from Core-Cell1 weekCarbon Overlay2 m^200RIT Baja1 dayResin Overlay 1 gallon$65 $65 Buy from Core-Cell1 weekHardener1 quart$23.50 $23.50 Buy from Core-Cell1 weekMounting platesTotal of 1300 Machine shop/self machined3 days Hollow axle1 $0 - $20$0 - $20May custom order or 2 weeksSpring Pulley2$10 $20 Self machine/bearing from McMaster2 weeksAxle Pulley 2 $20 $40 Self machine/bearing from McMaster2 weeksSmall, Solid Axle100Self machine/bearing from McMaster2 daysBatteries1 – 16pk of AA NiMH$38 $38 Amazon2 weeks Gyroscope2 $25 $50 Pololu 2 weeks Current Sensor 6 $4 $24 Online (will update when known) 2 weeks Encoder 1 $90.63 $90.63 US Digital 2 weeks Bill of Materials (1)

Bill of Materials (2) Part name Quantity Cost/item ($/item) Total cost ($) Obtained Lead Times (estimated) Microcontroller (PCB) 2$50 or free$60Advanced CircuitsDecoupling components 10+ $0.05$1+Digikey, MouserMotor Isolation (PCB)2$50 $60 Advanced Circuits Motor Isolation (components) 10+$0.05$1+Digikey, Mouser Electronic Storage 1 Unknown Unknown Unknown

Part name Quantity Cost/item ($/item) Total cost ($) Obtained Lead Times (estimated) Motor 1 $299 $299 Teknic1 day – 4 weeksMotor Control Kit1$200 or free$200 TI 2 weeks Microprocessor220$40Not found yet1 weekWiresVarious (a lot)~$0.00$10 Hardware store/scrap2 days PVC Braces5 Not found yet<$20Not found yet 2 daysSprings 2<$20<$40McMaster Carr1 weekStringApprox. 10 feetUnknown $0 - $5Hardware store 2 days Voltage Sensor 6Not found yet <$40Online (will update when known)2 weeks Bike wheel100Member has unused bike to commandeer1 week Various FastenersVarious  $0 - $16.11 hardware store/scrap/McMaster5 days  Microcontroller Dev kit 1   up to $100 or free   $100 Texas Instruments TOTAL COST   $983.24 - $1128.24 (this is with $200 learning MC Kit) TOTAL COST   $783.24 - $928.24 (w/o learning MC Kit) Bill of Materials (3)

Questions/Concerns?