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?