Week 4 - Specification Report

Hello!

This is group 1's specification report.

We will be covering the flowing items below in order.

- Problem Statement

- Solution

- BOSCH XDK Sensor

- Material Selection- Ingress Protection (IP)

- Design

- Specfications

- Electrical Components

- Sensors

- Project Timeline

- Conclusion

Problem Statement

During the Learning Express(LeX) trip to Yogyakarta in March - April in 2016, a team of students helped to build a centrifugal pump for the housewives to humidify the mushroom farmhouse.

However, the housewives are unable to determine whether the farmhouse has the optimum levels of humidity and temperature for their mushrooms.

In addition, the housewives do not know when they need to humidify the farmhouse.

Therefore, the team is tasked to find a method to be able to measure the humidity and temperature levels of the farmhouse and collect data.

Solution

BOSCH has partnered with the team by providing their XDK sensor to measure the humidity and temperature.

BOSCH XDK Sensor

The XDK sensor provided by BOSCH is a fully integrated Cross Domain Development Kit. It consists of both hardware and software which has the following Microelectromechanical (MEMS) devices like an accelero-meter, magnetometer and gyroscope in addition to humidity, pressure, temperature, acoustic and digital light sensors.

To add on, the XDK also includes a micro-controller, integrated antennas, a micro-SD card slot and a rechargeable battery. Multiple wireless technologies ensure connectivity and access to the Internet.

The included software development environment and operating system offer access to different Application Programming Interface (API) layers, which allow the user to program at their preferred depth.

Material Selection

Main Characteristic:

Waterproof
Breathable
Durable
Corrosion resistance
Not Biodegradable
High toughness
Easy to find
Toughness in elevated temperature
Affordable
Easy to fabricate

The team will be doing a material selection for the Main Cover Structure and the mounting of the XDK

Main Cover

For the main cover, the team will be using a strong structure to withstand the outdoor environment. The material also has to be light weight.

Mechanical Properties:

Low specific gravity - 30%
Low in water absorption -30%
High modulus of elasticity - 10%
High Toughness - 10%
High temperature resistance - 5%
Affordable - 15%

Materials

ABS
Acrylic
Expanded PVC
HDPE
Polycarbonate
SentryGlas® Interlayer

The definition for the requirement

Primary Selection Table for Main Cover

The team will rank the materials whereby (5) means an excellent material choice and (1) for a poor choice. (0) means it will not be considered at all.

Information from the table above was obtained from the following website:

https://www.curbellplastics.com/Research-Solutions/Plastic-Properties

After comparing, the team has decided to eliminate the Expanded PVC because of the low mark it received compared to the other materials.

The team would also eliminate SentryGlas@Interlayer because it is missing some information.

As such, the remaining materials will be undergoing the secondary selection.

Manufacturing Process:

blow molding
casting
compression molding
extrusion
fabrication
foaming
injection molding
rotational molding
thermoforming of sheet

Materials that can be manufactured in the lab are:

Fabrication( workshop process and CNC)
Extrusion ( 3D printer)
Foaming ( Vacuum Press)

The team will consider the following aspects before manufacturing our prototype:

Cost and availability - 50%
Chances of Failure - 20%
Availability of the machine - 10%
Time Taken - 20%

Secondary Selection Table for Main Cover

Prices are taken from: www.monotaro.sg

After the second selection, the team has eliminated the ABS and HDPE because they received one of the lowest marks.

Whereas Acrylic and Polycarbonate obtaieds the highest of 390% and 320% respectively.

Therefore, the team has chosen Acrylic and Polycarbonate and will conduct an advantage and disadvantage analysis.

Acrylic

Most acrylics are polymers of methyl methacrylate (PMMA).

Acrylic can be optically clear or cloudy, as in the case of impact modified acrylics.

ADVANTAGES:

Excellent optical clarity
Excellent weather-ability and resistance to sunlight
Rigid, with good impact strength
Excellent dimensional stability and low mold shrinkage
Stretch forming increases bi-axial toughness

DISADVANTAGES AND LIMITATIONS:

Poor solvent resistance; attacked especially by ketones, esters, chlorocarbons and aromatic hydrocarbons, freons
Subject to stress cracking
Combustible
Continuous service temperature limited to about 200 F degrees
Flexible grades unavailable

TYPICAL APPLICATIONS:

Transparent items such as lenses, automotive trim, household items, light fixtures, decorator items signage and point of purchase display .

Taken from : http://www.upcinc.com/resources/materials/acrylic.html

Polycarbonate (PC)

Although some structural variations are possible, the most common system is formed by reaction of bispenol A and phosgene.

Its applications are almost always those which take advantage of its unique high impact strength.

Recently, additional interest has resulted because of its low flammability. Some studies are currently underway to further improve this characteristic.

ADVANTAGES:

High impact strength
Low flammability
Thermoplastic processing methods

DISADVANTAGES AND LIMITATIONS:

Subject to stress cracking
Fairly high processing temperatures required (550 F)
Degrades upon extended residence time in processing equipment
Solvent resistance is only fair

TYPICAL APPLICATIONS:

Windows, helmets, instrument cases and mechanical goods

Taken from : http://www.upcinc.com/resources/materials/PC.html

Mounting of the XDK

Mechanical Properties:

Waterproof
Breathable
High Stiffness
High specific strength
High specific weight

Material:

Goretex
Sympatex
Hipora
polytetrafluoroethylene (ePTFE) membranes.
Elastomeric Pipe Penetration Sealing Gasket

Characteristic:

Waterproof and breathable at the same time
Availability
Design

Ingress Protection (IP)

As the XDK will be placed in the shelter with high humidity, around 85 to 95%, water particles may condense onto the XDK sensor and seep into the electrical components.

However the XDK is not fully water resistant and this may spoil the XDK.

Therefore, to protect the XDK sensor, the team has decided to design a casing for the XDK which prevents water from seeping in.

In addition, as there will be flies and insects in the mushroom farm, the casing has to be tight to ensure that the insects do not spoil the sensor. For example, biting off the wires.

To do so, the material has to have an IP of around 63 to 64.

IP 63 - "Dust tight" and protected against spraying water.

IP 64 - "Dust tight" and protected against splashing water.

Designs

After deciding on the materials and the characteristics that the team needed, we came up with some rough sketches on how our overall product would look like.

The design above is "Kinetic Box". The name was inspired from its purpose of being waterproof and breathable at the same time yet able to move certain parts of the box like a transformer.

The final design may be different from the current designs that we have.

This is just the team's current idea and changes may be made along the way as we come up with better ideas. Especially for the waterproofing of the box.