Problems

At Low-Inertia, we empower ambitious engineers with the resources / tools and opportunities to kickstart their careers and drive meaningful impact. 

Practical Problem Set

Navbar

SupabaseUserGlobalContext

FooterSection

Checkbox

Screen

UserLoginState

[Library] Tailwind 3.4 Number Tokens

react-awesome-reveal

[Library] Tailwind 3.4 Color Tokens

lottie-react

vanilla-cookieconsent

plasmic-nav

plasmic-embed-css

loading-boundary

plasmic-query

uuid

copy-to-clipboard

plasmic-basic-components

[Library] Tabler 3.2 Icons

Low Inertia

react-youtube

plasmic-tabs

react-aria

plasmic-cms

react-twitter-widgets

plasmic-rich-components

react-chartjs-2

antd5 hostless

tiptap

react-slick

react-parallax-tilt

react-quill

A catheter was returned as defective. The description to the failure says a malfunctioning camera at its tip (bad image). 

Sheet metal enclosure Design

There is an optics system with a camera and LED illumination source mounted on a linear actuator. The camera subsequently takes images of samples at 4 stations every 30 seconds.

What is the function of a bearing?

The heat conduction through the aluminum heater block

Sheet metal manufacturing: laser cutting versus punch press operations

Chassis Sheet Metal Design

First Law of Thermodynamics

Alignment Assembly Fixture: Using dowel pins

Technical Assessment # 1

Bernoulli’s Equation

Static equilibrium

3D printing a spur gear

What is the main difference between casting and forging?

Camera triggering over serial communication

Speed Reduction Ratio

Establishing Serial connection to the motion controller with python

Heat Transfer

LED on Metal Core PCB 

What is natural frequency?

A batch of injection-molded plastic housings for a consumer electronics device (e.g., a remote control) was rejected due to visible surface defects (sink marks and warpage) at the supplier. 

List Methods to Fasten Components to Aluminum Sheet Metal Chassis

Instructions
These Questions mimc take-home technical assessment that many companies (especially startup) ask the candidates to complete. In actual interview, you&rsquo;ll typically have 1-2 hours. Don&rsquo;t be discouraged if it&rsquo;s tough. We will help you learn! If it&rsquo;s not, you&rsquo;re well-prepared!
<ol>
<li dir="ltr">Assume designs are for mass production and cost, assembly, and reliability needs to be considered.</li>
<li dir="ltr">Sketches alone may not show subtle decisions&mdash;explain assumptions and reasoning for context. Try to show your work; sketches reveal your problem-solving process.</li>
<li dir="ltr" style="font-weight: bold;">You can submit your answers in the form below for personal feedbacks</li>
</ol>
This will be a great practice. Good luck!
&nbsp;
<hr>
&nbsp;
Question 1
There is a water-filled chamber with two hot plates directly beneath it, each equipped with its own cartridge heater and thermistor for independent temperature control. In order for certain reactions to happen, the chamber needs to have an area between 31&plusmn;1C and 88&plusmn;1C.
Assumption: Uniform and correct temperature in the hot plates. Only consider steady state. Don&rsquo;t worry about the initial heating. The chamber is made out of acrylic.
<img style="width: 500px; max-width: 100%; height: auto; display: block; margin-left: auto; margin-right: auto;" src="https://img.plasmic.app/img-optimizer/v1/img?src=4c1a9e294c5645f0a424fe11471d829d.png&amp;f=webp&amp;q=75" width="336" height="150">
<ol>
<li>Draw a simple sketch of what you would expect the temperature gradient to look like at steady state</li>
<li>Draw a simple sketch of what you would expect the zone of 32&plusmn;1C and 88&plusmn;1C would be located.</li>
<li>What would happen if the chamber was made out of the following materials instead?
<ol>
<li>Glass</li>
<li>Aluminum</li>
</ol>
</li>
<li>In real life without making any assumptions, what can go wrong in this design? How would you mitigate it?</li>
<li>How would you optimize this design to maximize volume of 32&plusmn;1C and 88&plusmn;1C zones.</li>
</ol>
&nbsp;
Question 2
<ol>
<li>Assess the design&rsquo;s strengths and weaknesses, highlighting any critical flaws or benefits.</li>
<li>Suggest potential improvements to enhance the system.</li>
<li>Identify possible second-order effects that may need further analysis or testing.</li>
</ol>
<img style="width: 500px; max-width: 100%; height: auto; display: block; margin-left: auto; margin-right: auto;" src="https://img.plasmic.app/img-optimizer/v1/img?src=27be0ac287ce5c4ea59a35dbbd2937b8.png&amp;f=webp&amp;q=75" width="376" height="169">
&nbsp;
Question 3
A future prototype needs a subsystem to deliver even clamping pressure to an assembled consumable with this geometry. There is a 2mm zone between the raised and lower surfaces where clamping pressure isn&rsquo;t required. The thickness of the parts are irrelevant. Let&rsquo;s assume that they have stainless steel backing.
<img style="width: 500px; max-width: 100%; height: auto; display: block; margin-left: auto; margin-right: auto;" src="https://img.plasmic.app/img-optimizer/v1/img?src=bd8e060816a5d9a7b692227d11c66e76.png&amp;f=webp&amp;q=75" width="419" height="105">
The requirements are as follows:
<ol>
<li dir="ltr" role="presentation">The system needs to apply 15 PSI evenly across the entire surface of 1 sq in</li>
<li dir="ltr" role="presentation">The force distribution across the area needs to be less than 2 lbf.</li>
<li dir="ltr" role="presentation">The system goes through 1 million cycles of heating and cooling between 120 F to 35F.</li>
<li dir="ltr" role="presentation">This clamping system needs to be completely automated.</li>
</ol>
Design a high-level system design that would achieve this. Also, How would you verify that the requirements are being met?

dlxmedia-hu-pakTZIspHO0-unsplash.jpg

<span data-slate-fragment="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">A catheter was returned as defective. The description to the failure says a malfunctioning camera at its tip (bad image). The camera is potted with UV-cure adhesive within the cavity at the tip and connected using a micro-coaxial cable which is snaked through the lumen (a hollow channel or passageway within the catheter shaft) the shaft of the catheter. Identify potential failure modes and explain the steps you would take to investigate and determine the root cause.

Determine the temperature at the cartridge heater embedded in a perfectly conductive material on the inner surface of a 0.1 m thick aluminum wall (thermal conductivity k = 200 W/m&middot;K, area A = 1 m^2). The cartridge heater provides a steady-state heat flux of 20000 W/m^2 through the wall via conduction. The outer surface of the wall is in perfect thermal contact with a consumable cartridge, which is maintained at a constant temperature of 30&deg;C to facilitate a heating process. Ignore radiation effects. What is the temperature at the cartridge heater (inner surface of the wall)?

<div>When attempting to establish a serial connection to the motion controller with the provided script, a <code>ModuleNotFoundError</code> occurred. What is the most common the reason for this error?</div>
<div>&nbsp;</div>
<img style="max-width: 100%;" src="https://img.plasmic.app/img-optimizer/v1/img?src=a00f1c6bc9177c2c79a66be4689414a0.png&amp;f=webp&amp;q=75" alt="Motion controller connection diagram">

A batch of injection-molded plastic housings for a consumer electronics device (e.g., a remote control) was rejected due to visible surface defects (sink marks and warpage) at the supplier. The housings are made from ABS using a single-cavity mold with a cold runner system. Identify potential failure modes and outline the steps to investigate and determine the root cause.

There is an optics system with a camera and LED illumination source mounted on a linear actuator. The camera subsequently takes images of samples at 4 stations every 30 seconds.
<img style="width: 500px; max-width: 100%; height: auto; display: block; margin-left: auto; margin-right: auto;" src="https://img.plasmic.app/img-optimizer/v1/img?src=d06be59e9cf54ae843fddc27f5255a0b.png&amp;f=webp&amp;q=75" width="385" height="149">
<ol>
<li>Once all components were installed, you began gathering images. However, the image captured at station 1 is blurry. Identify all potential reasons that could lead to this issue.</li>
<li>Drawing from your responses to question 1, Identify Important requirements for this setup.</li>
</ol>

You are tasked with designing mechanical support for an optics setup using an MCPCB-mounted LED. Using the information below, answer the following questions:
&nbsp;
<img style="max-width: 100%; height: 122px;" src="https://img.plasmic.app/img-optimizer/v1/img?src=68fae0ab05af54f61e9b22b99cea398b.png&amp;f=webp&amp;q=75" alt="LED optics setup image" width="264">
<a href="https://www.thorlabs.com/drawings/942922c46680c590-63C8436E-A145-53FC-1714E2B1407E797F/M565D2-SpecSheet.pdf" target="_blank" rel="noopener">Link to the specification document</a>
&nbsp;
<ol>
<li>What color would you expect this LED to be?</li>
<li>Sketch the expected illumination intensity distribution on the object at focal distance (1D and 2D).<img style="max-width: 100%; height: auto;" src="https://img.plasmic.app/img-optimizer/v1/img?src=76dd33d2288c09d6601c865b7e284e3f.png&amp;f=webp&amp;q=75"></li>
<li>Explain how you would further improve the illumination intensity uniformity.</li>
<li>What are the key design considerations for the mounting setup fixture?</li>
</ol>

You are tasked with 3D printing a spur gear (~20 mm outer diameter, 3 mm thickness) for preliminary low-torque feasibility testing.&nbsp;
&nbsp;
<img style="max-width: 100%; height: auto;" src="https://img.plasmic.app/img-optimizer/v1/img?src=14b1e59540eab6b126070abdc2a411c3.png&amp;f=webp&amp;q=75">
<ol>
<li>
How would you orient the part on the printer (explain your reasoning) and roughly estimate how long this would take
<ul>
<li>
FDM (PLA; 15% infill; standard layer height: 0.2mm)
</li>
<li>
SLA (Standard formlabs resin: white/grey/black); include post processing time
</li>
</ul>
</li>
<li>
Identify the key risks associated with each approach (e.g., mechanical strength, surface finish, dimensional accuracy
</li>
<li>
Suggest minigation strategies
</li>
</ol>
&nbsp;
Notes:
<ul data-start="693" data-end="949">
<li class="" data-start="693" data-end="782">
Assume dimensional precision (gear meshing) is moderately important but not critical.
</li>
<li class="" data-start="785" data-end="870">
Assume that low-torque testing means forces up to 1&ndash;2 N&middot;cm on the gear teeth.
</li>
<li class="" data-start="873" data-end="949">
Include post-processing time (e.g. surface polishing, SLA washing/curing) in your estimates.
</li>
</ul>

What is the First Law of Thermodynamics?

What does Bernoulli&rsquo;s Equation describe?

What are the three modes of heat transfer?

What conditions must be satisfied for an object to be in static equilibrium?

What is the main difference between casting and forging?

What is the function of a bearing?

A motor gear with 10 teeth drives a large gear with 50 teeth. What is the speed reduction ratio?

Using the manual below, write a simple python script to send the commend to the camera to start recording over serial (serial port = '/dev/ttyUSB0' and confirm that it was received and processed. Don't worry about error handling
&nbsp;
&nbsp;
<hr>
&nbsp;
High-Speed Camera Serial Communication Manual&nbsp;
&nbsp;
1. General Information
<ul data-start="208" data-end="412">
<li class="" data-start="208" data-end="234">
Baud Rate: 19200 bps
</li>
<li class="" data-start="235" data-end="253">
Data bits: 8
</li>
<li class="" data-start="254" data-end="272">
Parity: None
</li>
<li class="" data-start="273" data-end="291">
Stop bits: 1
</li>
<li class="" data-start="292" data-end="316">
Flow Control: None
</li>
<li class="" data-start="317" data-end="342">
Encoding: Raw bytes
</li>
<li class="" data-start="343" data-end="412">
End of Transmission: No termination character (binary protocol)
</li>
</ul>
&nbsp;
2. Command List
&nbsp;
<div class="_tableWrapper_16hzy_14 group flex w-fit flex-col-reverse" tabindex="-1">
<table class="w-fit min-w-(--thread-content-width)" style="border-collapse: collapse; border-color: rgb(0, 0, 0); border-style: solid;" border="1" data-start="439" data-end="1077">
<thead data-start="439" data-end="530">
<tr data-start="439" data-end="530">
<th style="border-color: rgb(0, 0, 0);" data-start="439" data-end="461" data-col-size="sm">
Command Name
</th>
<th style="border-color: rgb(0, 0, 0);" data-start="461" data-end="489" data-col-size="sm">
Hex Sequence
</th>
<th style="border-color: rgb(0, 0, 0);" data-start="489" data-end="530" data-col-size="sm">
Description
</th>
</tr>
</thead>
<tbody data-start="623" data-end="1077">
<tr data-start="623" data-end="713">
<td style="border-color: rgb(0, 0, 0);" data-start="623" data-end="645" data-col-size="sm">Trigger Capture</td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="645" data-end="674"><code data-start="647" data-end="663">0xA5 0x5A 0x01</code></td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="674" data-end="713">Capture a single frame immediately.</td>
</tr>
<tr data-start="714" data-end="804">
<td style="border-color: rgb(0, 0, 0);" data-start="714" data-end="736" data-col-size="sm">Start Recording</td>
<td style="border-color: rgb(0, 0, 0);" data-start="736" data-end="765" data-col-size="sm"><code data-start="738" data-end="754">0xA5 0x5A 0x02</code></td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="765" data-end="804">Start continuous video recording.</td>
</tr>
<tr data-start="805" data-end="895">
<td style="border-color: rgb(0, 0, 0);" data-start="805" data-end="827" data-col-size="sm">Stop Recording</td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="827" data-end="856"><code data-start="829" data-end="845">0xA5 0x5A 0x03</code></td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="856" data-end="895">Stop continuous video recording.</td>
</tr>
<tr data-start="896" data-end="986">
<td style="border-color: rgb(0, 0, 0);" data-start="896" data-end="918" data-col-size="sm">Get Status</td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="918" data-end="947"><code data-start="920" data-end="936">0xA5 0x5A 0x04</code></td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="947" data-end="986">Request camera operational status.</td>
</tr>
<tr data-start="987" data-end="1077">
<td style="border-color: rgb(0, 0, 0);" data-start="987" data-end="1009" data-col-size="sm">Reset Camera</td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="1009" data-end="1038"><code data-start="1011" data-end="1027">0xA5 0x5A 0xFF</code></td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="1038" data-end="1077">Reset the camera to default state.</td>
</tr>
</tbody>
</table>
<div class="sticky end-(--thread-content-margin) h-0 self-end select-none">
<div class="absolute end-0 flex items-end">&nbsp;</div>
</div>
</div>
&nbsp;
3. Expected Responses
&nbsp;
<div class="_tableWrapper_16hzy_14 group flex w-fit flex-col-reverse" tabindex="-1">
<table class="w-fit min-w-(--thread-content-width)" style="border-collapse: collapse; border-color: rgb(0, 0, 0);" border="1" data-start="1110" data-end="1375">
<thead data-start="1110" data-end="1158">
<tr data-start="1110" data-end="1158">
<th style="border-color: rgb(0, 0, 0);" data-start="1110" data-end="1126" data-col-size="sm">Response Code</th>
<th style="border-color: rgb(0, 0, 0);" data-start="1126" data-end="1158" data-col-size="sm">Meaning</th>
</tr>
</thead>
<tbody data-start="1209" data-end="1375">
<tr data-start="1209" data-end="1265">
<td style="border-color: rgb(0, 0, 0);" data-start="1209" data-end="1225" data-col-size="sm"><code data-start="1211" data-end="1217">0x00</code></td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="1225" data-end="1265">OK (Command received and successful)</td>
</tr>
<tr data-start="1266" data-end="1315">
<td style="border-color: rgb(0, 0, 0);" data-start="1266" data-end="1282" data-col-size="sm"><code data-start="1268" data-end="1274">0x01</code></td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="1282" data-end="1315">Error (Invalid command)</td>
</tr>
<tr data-start="1316" data-end="1375">
<td style="border-color: rgb(0, 0, 0);" data-start="1316" data-end="1332" data-col-size="sm"><code data-start="1318" data-end="1324">0x02</code></td>
<td style="border-color: rgb(0, 0, 0);" data-col-size="sm" data-start="1332" data-end="1375">Busy (Camera cannot accept command now)</td>
</tr>
</tbody>
</table>
<div class="sticky end-(--thread-content-margin) h-0 self-end select-none">&nbsp;</div>
</div>
&nbsp;
All responses are a single byte.

In designing a sheet metal enclosure, what factors must be considered when determining the bend radius and material thickness to prevent failures during forming?

What are the key considerations when designing a sheet metal part for laser cutting versus punch press operations?

What are the advantages and potential drawbacks of using dowel pins for locating parts in an assembly fixture?

An engineer designed a chassis using 2.4mm stainless steel sheet metal, as depicted in the image below.
The design includes a separate brace part that will be mounted to cover the open face and enhance structural integrity (Mouting features not shown). What could a major flaw in this chassis design?
<img style="max-width: 100%; height: auto;" src="https://img.plasmic.app/img-optimizer/v1/img?src=112f4c0ab09fe7bce19d4f56a980e026.png&amp;f=webp&amp;q=75">

You are tasked with designing a lightweight electronics enclosure using 2mm aluminum sheet metal for a small control panel. The enclosure must house sensitive components and be securely mounted to a wall while allowing easy access for maintenance. What are the methods would you consider using to fasten the components to the aluminum sheet metal chassis&nbsp;

Practical Problem Questions