Critical Design Review12/7/04
Team UnoBunker Curnes
Shawn HoulahanStephanie Rohrs
Steve SchwallChuck Smith
Objective
Design and build an intelligent device that provides continuous shade for a
defined volume.
Key Requirements
Must shade a 2’ x 3.5’ x 5’ rectangular prism1 that is 1.5’ above the ground while the sun is above 30° from the horizon
50lbs max weight2
Function in winds up to 25mph3
Must provide 12hrs of
shade
1 National Center for Health Statistics2 National Institute for occupational safety and health3 Australian Government Bureau of Meteorology
Key Requirements
Material selected for fabrication must be water, rust, and corrosion resistant
Must have a manual turn on/off option
Maximum repositioning time must be under a minute
Noise volume of the device must be under 60 decibels4
All electronics and power sources must be enclosed in waterproof casings
4 League for hard of hearing
Result – The SmartShade
Two degrees of motion
Tilt joint and rotational joint
Triangulated sensor array
Mechanically functional prototype
Functional control logic
Attempts to orients umbrella towards sun
Motor control issues
Tilt Joint Requirements Required Motor Torque
T=(F*dm/2)((1+pi*f*dm)/(pi*dm – f*l))
F = force transmitted to
screw by four-bar linkage
Torque on Pin
F = (Cd) *(.5p*V^2*A)
Cd = 1.2
Tilt Joint Design
1. The motor drives the threaded rod.
2. The threaded rod causes the collar and connecting rod to rise or lower depending on the motor direction.
3. As the connecting rod moves it causes the triangle and upper pole to tilt.
Tilt Joint Demo
Tilt Joint Demo
Tilt Joint Demo
Tilt Joint Demo
Power Screw
Held in position by two Delrin disks
Load supported by two thrust bearings
Connected to motor shaft by coupling
Length of threaded region on threaded
rod equal to amount of thread needed for
stroke
Rotation Joint Requirements
Torque on Pole
F = (Cd) *(.5p*V^2*A)
Cd = .6
Required Motor Torque
Maximum torque
requirement when
umbrella tilted 60°
Rotational Joint Design
Chain Driven
3.89:1 Mechanical Advantage
Pole Supported by 3 Delrin Bearings
Rotational Joint Demo
Motor Selection and Power For rotational motion, a speed of 1/3 rpm and a torque rating of 16 ft lb was
needed
Purchased motor:
4 rpm
4.16 ft lb torque
For the tilting motion, a speed of 84 rpm and a torque rating of 1.3 ft lb was desired
Purchased motor:
47 rpm
2.33 ft lb torque
Since both motors were 24 V DC, two 12 V DC batteries were used in series
Control Logic - Overview In order to shade our specified area
continuously, the umbrella must always be oriented towards the brightest light source.
To accomplish this, three sensors are placed in a triangular pattern around the canopy.
When all three sensors are equal, the umbrella is pointed towards the sun.
Sensors
Three photo-diode sensors are used in an isosceles triangle pattern
Output .6 V in direct sunlight
As light goes down, output varies linearly to zero
Op-Amps and resistors provide a gain of 9 to microcontroller
Control Logic
Light Sensors Microcontroller MotorsInput Output
Changes in motor positions change input from light sensors
Microcontroller receives input from light sensors one and two and moves the rotational motor until the two sensors are equal.
Once sensors are equal, the microcontroller receives input from sensor three and moves tilt motor until all three sensors equal.
When all sensors are equal, system sleeps for 15 minutes.
1 2
3
Enhancing Control Logic
Initialize
Check Sensors 1 and 2
Move Motor 1
Check Sensor 3
Move Motor 2
Wait 15 minutes
For the sensor and op-amp assembly, a resolution of +/- 1% is possible. The difference of 1% in output voltages is .04 V.
If overshoot occurs, the program can be designed to automatically account for this and reverse direction until the sensors are within their specified range.
Once the sensors return a value less than 3V (dusk), the system repositions itself to vertical.
Capabilities
Prototype
Tilts 60 degrees from vertical
Rotates 360 degrees
Moves from initial position to desired position in 90 seconds or less
Easy to open and close
Final Product
Can reposition itself to continuously shade a defined volume
Motor control
Control logic
Conserves power by sleeping when dark
Able to function for 30 days before batteries must be recharged
Features
Simple user interface
Does not interfere with sitting users
Low maintenance
Portable
Rechargeable batteries
Can be disassembled for storage
Safe adjusting speed
Budget
Total Budget Allowance: $500
Total Amount Spent: $499
Electronics 17%
Fasteners 4%
Shipping & Handling 12%
Upper Assembly 32%
Lower Assembly 35%
Future Design Considerations
Integration motor into pole
Weatherproof casings
Wind vents in umbrella
Operating Noise
Future Design Considerations
Aesthetics
Tilt joint
Base
Materials
Safety issues
Exposed wires
Pinch points
Additional Features
Radio, beverage cooler, cup holders, built-in chairs
Questions?