TDJ3M

Mechanical Design

While often referred to as mechanical engineering, mechanical design is the discipline of engineering that applies the principles of physics and materials science for analysis, design, manufacturing, and maintenance of mechanical systems. It is one of the oldest and broadest engineering disciplines.

[source]

Simply put - mechanical engineering is the study, design and maintenance of mechanical things. While modern mechanical engineering was birthed during the industrial revolution in a variety of ways mech.eng. has been around for a LONG time. Some of the earliest written references to mechanical engineering include the MANY works of Archimedes in c. 287-212 BC). Archimedes lived in Syracuse (a Greek city-state) and was under the constant threat of invasion by Rome. As such, many of Archimedes' inventions are machines of war - including the ship claw ship trebuchet (2), and the scorpion, but Archimedes also invented other mechanical engineering marvels that transformed civilization such as the water screw (to move water), and the water organ.

Other notable early historical mechanical engineers include Da Vinci, Zhang Heng, Ibn Ishaq Al-Kindi, Al-Fraganus, Al-Jazari (and many other Islamic visionaries from the 'golden age of Islam' [500AD-1500AD]. Newton, then afterwards industrial revolution era engineers quickly filled the world with marvelous machines of varying designs. Once the industrial revolution started, the 'civilized world' was transformed quickly (a list of major historical engineering advances).

Engineering

in general is the study and design of systems, materials, machines and processes to solve a problem. In many ways engineering is what humans do best. Think creatively about a problem, then come up with a solution. This solution is often a way of automating, or interacting with the world around us in a way that makes our lives easier or better. Arguably many aspects of architecture, industrial design, and other such disciplines fall under engineering. Likewise most physical disciplines in the world have aspects of engineering built into them.

Assignment #5 - Cranewars!

We will use the design cycle to come up with a product that will address the following goal:

Design a crane, using limited materials, that will be both easy to use and compete in a time trial and able to lift a minimum of a 1kg weight.

Description:

Cranes are built with the intention that they remain upright even under strong loads and shear forces. The purpose of this activity is to construct a crane that will remain upright and intact as it picks up 1kg weights and relocates them in an arc 90 degrees to the base of the crane from where they started.

General Rules:

The crane must be built entirely in the classroom/shop. The crane is a minimum of 60cm tall. The weights are placed 20cm from the base of the crane. The crane must pivot to deliver the load 90 degrees from the base from where it started. The crane's tower cannot simply be frictionally rotated with no moving parts. All crane manipulation must be made through non-direct interaction with the crane (i.e. controllers. They may be strings, wires, cords, but you can't simply manually swing the boom or the base)

There are 2 parts to the competition:

1) See how many 1 kg weights are moved from the 'staging area' to the 'work site' in 60 seconds

2) See how much weight the crane can pick up all at once before it breaks.

Materials:

The crane is to be built out of 12 mm x 4 mm pine strips (roughly 2x6 scaled in metric) bonded by wood glue. You will also be given 2 sheets of white paper. No other materials may be used in the manufacturing of the structure.
Other materials may be used for the gripping pieces, rigging and pivot materials but must not be specific to grappling (e.g. you cannot go out and buy a winch and a robotic hand)
Cut wood pieces can be of any length - I will typically supply 1m long pieces.
10 m of 'scaled 2x6' wood will be supplied to the team.
One sheet base will be supplied to the team.

Construction:

All construction must be completed prior to the test date - allow at least 24h for a full cure before testing
Laminating wood members is allowed (but likely you won’t have the extra wood to do so).
Glue can only be placed between two separate pieces of wood and in wood gaps. You cannot coat an entire piece of wood with glue without connecting directly to the surface of another piece. When laminating members together, glue may only be placed between the touching wood surfaces. If glue bleeds between the surfaces and/or connections, it must be sanded off so it will not provide rigidity to the member. I will determine if the glue provides support to the structure.
Any method of securing the crane to the base is acceptable.

Crane Dimensions:

The crane must have an interior area of no less than 100 cm2. The boom arm must have an interior area of no less than 30cm2.
A sheet of thin wood will be given as a base
The crane must exceed, or be equal to, 60 cm in height.
The weights will be placed 20 cm. away from the base. Thus the boom arm must be able to reach out 20 cm.

Testing:

All cranes will be impounded at the beginning of the competition (no work or adjustment may take place once testing begins)
Eye protection has to be used since when the crane shatter they could yield fast moving fragments of wood under high speed. TRUST ME.
The crane must be able to lift a single 1kg weight. If it cannot, then the crane will have failed with no results.
All contestants are expected to follow the engineering rule of ethics (no cheating). Failure to comply will result in forfeiture of a grade. Your crane will be loaded to destruction as demonstrated.
In the speed competition, the 1kg weights will be moved as quickly as possible. The winner is the one that is able to move the most 1kg weights from the staging area to the 'work area' in 60 seconds.
In the weight competition, the weights will be added to a bucket hanging off the table. Once the structure breaks the highest recorded weight added up to that point will be the one recorded.

Evaluation:

Before construction begins - an isometric sketch & orthographic projection must be submitted for assessment. After completion, a final isometric drawing and orthographic projection will be submitted in the design report. The isometric drawing will include all relevant details as pullouts. You will use these in guiding your construction.
AutoCAD file - will be included in the design report
Crane construction - overall design of the finished product will be evaluated including: dimensions, style and adherence to the working drawings.
Design report (EXEMPLAR)

General value of various components of the project:

Rapid Prototyping and additive printing

Critical to Mechanical Design is the use of both CAD software (we use AutoCAD here at SC) as well as 3D programs such as Inventor. To that end, in the past decades fast replicators (though technically it's rapid prototyping) known collectively as 3D printers, bring the 3D drawings to life. In rapid prototyping typically a resin or polymer (though it can be sand or metal) is subjected to a binder which can either be chemical or light (either for heat, or for converting a chemical structure). The 'scribe head' passes over the material in an X,Y plane, but then passes in consecutive Z layers until the product is manufactured. While not useful for large runs, rapid prototyping is very useful to get a good idea of how a mechanical engineer's design will work out on a small scale. If there are no further design alterations, then the design is sent to be manufactured writ large. To date, cheap rapid prototyping machines cost roughly $1,500 to $20,000 whereas high-end RP's are easily higher than $60,000 (filling the vat on a high-end photopolymer machine can cost $50,000 alone!!!).

Sketchup! Our cheap and easy 3D modeling software

3D modeling is the process of developing a mathematical representation of any three-dimensional surface of object (either inanimate or living) via specialized software. The product is called a 3D model. It can be displayed as a two-dimensional image through a process called 3D rendering or used in a computer simulation of physical phenomena. The 3D model allows designers to problem-solve, share their ideas in a more tangible way with other people, and lastly, to export to 3D printers - if the materials allow it.

All 3D programs share the same basic components in that they have to represent 3D space in 2 dimensions. The solution is to use projective geometry which transforms shape vectors (lines, curves, spheres, boxes etc...) into a 2D line which can be displayed on the screen. These lines are often colour-coded, or displayed with alpha-dissolves (same colour, but made more faintly) to make it easier to see the dimensions on the screen for the designer.

Some 3D modeling programs include Sketchup, form-Z, Maya, 3DS Max, Blender, Lightwave, Modo, solidThinking, SolidWorks and many more.

We will be using Sketchup for our 3D modeling. Not only is it free, but it has quite a powerful set of tools available to us that are fairly intuitive.

Please visit my Sketchup tutorial page for detail basics on how to use Sketchup software.

Some tricks to using Sketchup

Always ensure that you're using lines that follow the x, y, and z axes. The lines will flash green, red or blue if you're drawing correctly down one of these axes.
When possible, draw a guide before drawing a line/shape. It will ensure you get the correct distance. You can draw a guide by using the tape measure tool (toggled with control to get the 'plus' symbol), or the protractor tool for an angle (toggled with control once you've decided the angle reference).
Middle-mouse (MMB) click orbits your project, while holding shift+MMB allows you to pan your sheet in the current view (slide it around).
Spacebar is the universal 'get out of here' shortcut (much like the Esc. key is in AutoCAD). It allows you to select lines or deselect lines.
While selecting, holding Shift down allows for multiple selections.
Dragging a marquee box to the right functions just like in AutoCAD (makes a selection if the selection is completely within the marquee). Dragging a marquee box to the left selects anything that falls even a little bit within the marquee (again, just like in AutoCAD).
In complex objects - ensure your layers are open and you're putting each new element on a new layer. E.g. - in a house drawing, the walls may be in one layer, while the floor is on another, and the roof on yet another.
componentize EVERYTHING. Hitting G and replacing current selection with your grouped object ensures that when you go to move something around it doesn't pull all the lines attached to it.
When push/pulling an object - toggle a new face by hitting Control before starting your push/pull. This creates a new face and doesn't leave a mess later on.
Work in the extended toolbar mode and learn your shortcuts!!!!

Assignment #6 - Sketchup Challenge

Once done previewing the videos - complete the Sketchup challenge (picture seen here below). Download this Sketchup shape to complete to your school account and use it to measure angles/lengths so as to get a perfect replica as exact as you can make it. Once done submit both a picture at the exact same angle (gotten by exporting a 2D graphic), and the sketchup file itself.

tdj3m_sketchup_Shape to copmlete.png

Assignment #xx - Trebu-tacular!

You are to create, in miniature, a fully functional trebuchet that is capable of launching a 100g weight no less than 1m distance. The goal is two part:

See who can propel the 100g weight the furthest
See who can be most accurate in hitting a target

Description:

The counterweight trebuchet appeared in both Christian and Muslim lands around the Mediterranean in the twelfth century (though was likely developed some 700 years earlier in China). It could fling projectiles of up to three hundred and fifty pounds (140 kg) at high speeds into enemy fortifications. This created a far more formidable siege engine than the catapult which was limited in both range and durability.

General Rules:

The trebuchet can be no taller from ground to the pivot point where the arm passes through of 30 cm. The arm itself can be no longer than 70 cm.The goals are to make both a robust design that is capable of launching a 100g mass as far as possible, but also to be able to be accurate for the second portion of the competition (given a couple of tries). In order to qualify for competition points, the 100g mass must launch no less than 1m from the trebuchet's arm's pivot point.

All contestants are expected to follow the engineering rule of ethics (no cheating). Failure to comply will result in forfeiture of a grade.

Materials:

Any wood materials are acceptable for the structure for this competition. Any other pieces must be supplied from home, but be subject beforehand to approval by me. No part of the trebuchet may be bought from parts especially designed for such activity. Wood glue will be the adhesive used to glue members of wood to each other. Allow a 24h cure time between the last stages of construction and the test date.

Testing:

1) Distance

You will attempt to launch a 100g mass as far as possible using your trebuchet. No interaction may be made with the device after you trigger it to release. The mass will only be able to be launched from the inertia given to it by the falling counterweight.

2) Accuracy

You will attempt to launch a 100g mass exactly 1.3 m away from the pivot arm of the trebuchet. You will get 3 attempts to do so. The average of the distance away from the 1.3 m mark will be taken as the competition entry.

Helpful Calculations

A very simple model found online just uses the mass of the projectile (m2), the mass of the counter weight (m1), and the height the counter weight falls (h):

Range (max) = 2 * (m1/m2) * h

Now the efficiency of the trebuchet will cause this model to be off by quite a bit. But once you have a working trebuchet, we find this model works well when we vary m1, m2, or h. We assume we have a take off angle of 45 degrees above the horizon. This solution is based on the classic max range ballistics problem - 45 degree take off angle. It also assumes converting all the potential energy of the counter weight to kinetic energy of the projectile. That is why the efficiency issue comes up as a lot of energy is lost due to friction in the moving trebuchet. If the projectile spins a lot then it will travel a shorter distance as the potential energy is split into kinetic and rotational energy. Projectile shape and wind will also vary the results.

Evaluation:

Before construction begins - paper sketches, and a 3D Sketchup model must be submitted for assessment. After completion, sketches, a final CAD file and a 3D model will be submitted with the design report. The Sketchup model will include all relevant details as pullouts.
From the isometric sketch, you are to create front and side views as well as top view of your trebuchet in AutoCAD. You will use these in guiding your construction.
Trebuchet construction - overall design of the finished product will be evaluated including: dimensions, style and adherence to the working drawings.
Distance results
Accuracy results
Self-Evaluation/ write-up.

Technical Report

Google Sites

Report abuse