Reverse Engineering

In this project, an extension of the Break it Apart challenge, we were tasked with reverse-engineering a common product which we had previously disassembled. This process involved discovering how every aspect of the device worked through extensive research about each subsystem, mechanism, and component. As a group, this meant conducting analysis of the object's:

Functions — how each subsystem works with the others, and how each mechanism works internally
Structures — how the device holds itself together, and how different elements are linked together
Materials — what the device is made of, and why that is important
Manufacturing — how each part of the device is made

After reverse-engineering the object, we then had to design a modification to the device which would improve it in some way. This was completely open-ended and could be anything, so long as it was a carefully-considered adjustment that would be feasible, practical, and beneficial to achieving the product's purpose.

Lastly, we were tasked with presenting our project both through a report document and a less-formal oral presentation (including a slideshow).

The Presentation and Report

Attached below are the presentation and the report. The report goes into much greater detail, while the presentation provides an overview and focuses more on the redesign portion.

Public: Reverse Engineering Presentation

Public: Reverse Engineering Report

Core Concepts

While there were relatively few concepts covered directly in-class, there were many concepts involved in the reverse engineering of the alarm clock specifically. Major concepts will be presented below.

Orthographic and Isometric Sketching

Sketching is the process of projecting a 3D object onto a 2D plane. Because this inherently loses one dimension of information, there are multiple ways in which the projection can be done. Two common projections are the orthographic and isometric projections.

An orthographic projection is like placing an object inside a glass box and looking at it through one of the panes. It provides a "flat" view from one of the sides of the object (left, top, front) which erases all depth information in that direction. This means that in such an orthographic projection, right angles in 3D space will remain right angles when projected to the 2D space, and the distances are also preserved. Below is an example of an orthographic projection of a 3D object.

While it is the central point which makes true the advantages above, one downside of an orthographic projection is that you do lose 100% of the information along one dimension. This means that several orthographic projections are needed to gain a more complete understanding of an object, and even still it can be difficult to visualize. An isometric projection avoids these problems by showing an object "corner-on". In an isometric projection, parallel lines in 3D space remain parallel when projected to the 2D sketch — that is, there is no vanishing point. But because the object is shown corner-on, instead of side-on as in an orthographic sketch, it is possible to see more of it at once. The left side of the sketch above is actually an isometric projection. Notice how the corners are facing the viewer (for example, the corner to the left and above the text "right side"). Also notice that right angles are not preserved in this projection, but rather become multiples of 60° angles (for corners facing the viewer, this is 120°, but for others it is 60°). Thus, each projection has its own benefits, and both can work in tandem to gain a greater understanding of the object at hand.

Gear Ratios/Reductions

One of the core elements of the alarm clock is the gearbox. The gearbox is the central element of the clock because it performs the key function of converting the one-revolution-per-second rotation of the drive gear into accurate rotation of the second hand (one revolution per minute), the minute hand (one revolution per hour), and the hour hand (one revolution per 12 hours). To do this, the gearbox utilizes gear ratios to reduce the rotational speed of the drive gear into the various speeds necessary.

Gear ratios work on the basic principle that a larger gear has more teeth than a smaller one. When two gears mesh and rotate, they each are moving at the same rate of "teeth per second" — they must be, or else their teeth would not stay aligned and the gears would grind. This means that when meshed with a smaller driving gear, a larger gear will move at the same rate of "teeth passing per second" as the smaller one, but because the larger gear has more teeth around its circumference, it takes more teeth to complete one revolution, and thus the larger gear will complete one revolution slower than the smaller gear. In other words, the larger gear will rotate slower. The same is true vice-versa; when the driving gear is larger, the smaller driven gear has less teeth per rotation, so it will complete its rotation faster (rotate faster). This basic principle allows you to convert a rotation at one speed into a rotation at another speed through two gears.

However, the problem with using only two gears is that a large reduction will result in a very large driven gear. This may soon become impractical for the device. Instead of this, gears can be chained together in a "gear train", where each pair of gears in the train performs one reduction. In this way, instead of performing one large reduction at the start, a gear train performs several small reductions that total to the large reduction. Importantly, instead of being arranged in a line, the gears in a gear train may be collapsed into two columns where each gear meshes with the one in the other column below it. This is a very compact scheme that allows for the best spatial efficiency, and is indeed the setup used in the alarm clock.

Magnetism and Electromagnetism

The clock's gearbox is driven by an electromagnet's interaction with a ring magnet mounted on a small drive gear. This interaction is crucial to almost any electronic device which moves. To begin, note that there are two parts to the interaction: the electromagnet, a coil of wire; and the ring magnet, a permanent magnetic dipole. The fundamental nature of the interaction is a magnetic interaction — which is, of course, a static electric field interaction modulo special relativity, but that is beyond the scope of this investigation. The magnetic interaction occurs when a magnet is placed in a magnetic field. Effectively, this means "when two magnets are placed near each other, they interact"; one may choose either magnet to "produce" the field and the other to interact with it, and the calculations will be the same.

Now, in more concrete terms, the common maxim of magnetic interaction is "like poles repel, unlike poles attract". When two magnets are placed near enough to each other, the north pole of one will attract to the south pole of the other, leading the two poles to touch. However, there is clearly no touching occurring within the clock gearbox. Rather, note that "like poles repel, unlike poles attract" is just a special case of the more general rule governing magnetic interaction: a magnet will attempt to align with the magnetic field it is in. This is the interaction which occurs when a compass needle rotates — the magnetic needle is simply trying to align with the magnetic field it is in, that of the Earth. This principle is the one which governs the interaction inside the clock gearbox. When the electromagnet produces a magnetic field, the ring magnet on the gear tries to align with the electromagnet's field, leading the gear to turn. When the electromagnet switches polarities, the ring magnet aligns again, rotating the gear further. This continues, leading the gear to continue rotating and driving the gearbox forward.

However, the question remains as to how the electromagnet itself generates a magnetic field. The simplest explanation is that a magnetic field is generated around any wire with current flowing through it, where the shape of the field is a circle around each point on the wire (see illustration below). When the wire is arranged into a coil, all these small fields align so as to add together, thereby leading to a large field being produced which is equal to the sum of all the small fields. When current flows through the coil, then, the large magnetic field is induced. (As aforementioned, why electricity moving through a wire induces a magnetic field is a matter of special relativity, which in brief can be summed as: length contraction means moving charges are actually closer together from the perspective of a stationary observer, meaning a wire with current flowing will have a greater charge density to that observer and will thus incur an attractive or repulsive static electrical interaction with the objects around it.)

The field produced by an electromagnet is the sum of the fields produced from each point on the wire.

Electrical Oscillators (Crystal Oscillators)

One major component of the clock is the crystal oscillator, which generates the pulses that drive the coil which drives the gearbox. The crystal oscillator is a kind of electrical oscillator. Electrical oscillators generate changing voltage at a specified interval with a given waveform — i.e, the shape of the signal output produced. There are a few main types of oscillator waveforms, shown below.

A typical crystal oscillator produces a roughly sinusoidal output wave (the second example on the left). It may be followed with a logical inverter, however, to convert this to a square wave (a digital ON-OFF oscillation).

The manner in which the crystal oscillator functions is determined by the intrinsic properties of the crystal itself. Crystals are effectively a resistor, inductor, and capacitor in series (with a parallel capacitor for intrinsic capacitance). Each of those components serves a unique purpose:

A resistor "resists" current. This means that with greater resistance, less current will flow at a given voltage.
An inductor is like a flywheel — it is difficult to get current to change its rate of flow through the inductor. This means that it will oppose current when there is no current flowing through it, but it will try to maintain current when there is already current flowing through it.
A capacitor is like a battery — it may be "charged" by applying a voltage, in which case current will flow through it until it is fully charged, and then may be "discharged", where current will flow back out through it into the circuit around it.

Combining these functions effectively creates the electrical equivalent of a weight mounted on a spring. The resistor is the friction inherent in the system trying to slow it down. The inductor is the inertial mass of the weight, which tries to keep it moving or stationary. The capacitor is the spring itself, pulling or pushing (charging or discharging) the weight. This analogy makes it clear why the crystal is the heart of the oscillator — a weight on a spring will move back and forth, oscillate, which is exactly what the current through a crystal will do when so prompted.

Just as a weight on a spring will eventually stop moving, however, a crystal alone does not suffice to produce endless oscillation. Instead, in must be driven by surrounding circuitry. Effectively, this means giving it a "push" when the weight is at either end of the spring. When a weight is thus pushed, it must be pushed in the opposite direction as it has been moving in order to amplify the oscillation — likewise, in the electric circuit, a NOT gate is employed to drive the crystal. The NOT gate inverts the voltage applied to it (a high voltage becomes low and a low voltage becomes high), which acts to continue "pushing" the current through the crystal in the opposite direction and amplify the oscillation.

With all this in mind, the below schematic for a basic crystal oscillator should appear relatively logical. Note the loop which connects the main NOT gate to the crystal.

Reflection

This project involved the coordination of multiple aspects and a decent amount of work with respect to the timescale, so I am happy with the result we achieved. One strong point for me during this project was my conscientious learning. I worked very diligently to complete the project and used a high level of detail in everything I wrote. Completing a 30 page report within the two week timespan (in addition to the presentation and actual research) required that I and my groupmates work methodically on the project each day and not fall behind in schedule. We certainly did so, and in the end I believe we produced a technical, professional report which accurately documented our reverse-engineering process. In addition, I think the critical thinking demonstrated on this project was excellent. We were able to design a creative solution which did not require any structural changes to the clock despite adding significant new functionality (a one-tap off switch for the alarm), something which tied into our original stated purpose of thinking deeply about pricing and manufacturing choices used in the design of the clock.

While we did well on the whole, our conscientious learning also had aspects that could be improved. At the start of the project, we were tasked with producing a Gantt Chart to structure our time and keep ourselves organized. While we never fell behind schedule or became disorganized, we did not stick to our Gantt Chart as much as we likely should have. This could suggest that either 1) we need to focus more closely on fulfilling our Gantt Chart each day, or 2) we need to make a more reasoned Gantt Chart which better reflects our actual scheduling patterns. I personally believe it was closer to the second option in this case, as we did function effectively and get everything completed with time before the deadline. In addition, our communication had one small pain point. Because we only had three members in our group, but the project had four main analysis components, we agreed to complete one section — material analysis — as a group. However, we could have communicated more clearly about what aspects of the clock we were each going to analyze as part of the material analysis beforehand. Because we did not do this, we each took pieces of it in patchwork, and while this did not prove to be any major detriment, the process could have been streamlined had we clearly designated which aspects were completed by which person. This being said, both issues above had a negligible effect on the actual outcome of our project, and can be easily rectified in the future. Overall, the project was a certain success.

Back to: STEM Senior Engineering

Page updated

Report abuse