SHIFT Learning by Design cooperative breathing installation

This paragraph appears in search results and previews for this page. In three to five sentences, summarize the whole project from background to result: what you designed, for whom, where and when, why it matters, and how it turned out. Write this last. It should make sense to someone who has never heard of your project, your client, or Humboldt County.

Describe the background of the project, covering who, what, when, why, and where: the client, the site, the course (Engr205 Introduction to Design at Cal Poly Humboldt), the semester, and your team. This page will be read by people around the world and in the future, so give enough context that a stranger understands it. Refer to your images in the text, e.g., Figure 1 shows the site before the project.

Images uploaded to Appropedia must be free to share and uniquely named. Start each file name with your project name, e.g., CCAT_compost_bin_background.jpg. Use File:Default.png as a placeholder until you have the real image. Give every image alt text (alt=) that describes it for readers using screen readers; the caption is what everyone reads, the alt text is what the image shows.

The objective of this project is to design, build, and test a... Write this so that a reader would know when the project is complete. You will refine this statement throughout the semester.

The cooperative breathing installation must help a child and an adult practice synchronized breathing through shared physical movement and calm visual feedback. This section identifies the required features, design considerations, and criteria that will be used to evaluate whether the installation meets the needs of the client and its users.

The specifications describe what must be included in the cooperative breathing installation and the conditions it must meet. The specifications for this project include:

• The client is the Child Development Association (CDA), with feedback provided by the client liaison.
• The installation must be designed for use by a child and an adult, instructor, caregiver, or peer.
• The device must include two manually operated handles that users push and pull while breathing.
• Each handle must provide an input that can be measured by the electronic control system.
• A microcontroller must compare the movement of the two handles and determine when the users are moving in synchronization.
• The device must provide clear visual feedback, such as an ambient glow, when the users' breathing movements are synchronized.
• The exterior must be soft or cushioned, free of sharp edges, and appropriate for use around children.
• The completed prototype must be portable enough for one adult to move and store.
• The design must operate from a safe, low-voltage electrical power source.
• The design and construction process must be documented on Appropedia so that the installation can be maintained or replicated.

In addition to the required specifications, the design must account for the following considerations:

• Different user ages, hand sizes, grip strengths, movement ranges, and abilities.
• Avoiding distracting lights, sounds, or other distracting stimulation
• The client's preference for a soft outer surface and an ambient glow.
• Pinch points
• durability during repeated use and accidental drops
• Smooth movements of the handles
• Sensor accuracy and calibrations
• Ease of cleaning and sanitizing surfaces
• Ease of repair
• Responsible use of materials, energy, and replaceable components

The criteria are the qualities our team will use to evaluate and compare possible designs, while the constraints establish the minimum requirements each design must meet. Table 1 lists the criteria, constraints, and relative weights for the cooperative breathing installation based on project requirements and client feedback.

Table 1: Example criteria and constraints for purchasing a chocolate bar. Replace with your project's criteria.

Criterion	Constraint	Weight (0–10, 10 highest)
Safety	The device must have no sharp edges, exposed wiring, accessible gears, or reachable pinch points.	10
Synchronization functionality	The device must detect movement from both handles and provide feedback when the users move together.	10
Durability	The device must withstand repeated pushing, pulling, classroom use, and accidental drops without becoming unsafe.	9
Ease of use	A child and an adult must be able to understand and operate the device with minimal instruction.	9
Sensory feedback	The feedback must be easy to understand, calming, and not overly bright, loud, or distracting.	8
Cost	The total cost of the device must not exceed $200	7
Comfort	The handles and exterior must be comfortable, soft, and appropriate for users with different hand sizes.	7
Charging	The device must be rechargeable, clearly indicate its charging status, and operate through several activities between charges.	6
Weight	The completed device must be light enough for one adult to carry and reposition without assistance.	6

The cooperative breathing installation will be used by a child and an adult, instructor, caregiver, or peer. During a short two-to-five-minute activity, the users will push and pull the handles while breathing together, and the device will provide visual feedback when their movements are synchronized. The device may be used several times per day under adult supervision. One functional prototype will be produced, and its design will be documented on Appropedia so others can replicate or improve it.

This literature review is an annotated bibliography. Introduce it in one to two sentences that name the topics covered and why they matter for this project. Group entries under topic headings (Client first, then 4-12 topics relevant to your design, such as materials, similar projects, local climate, or user needs).

Minimum sources per team member: one peer-reviewed journal article, one book, and two credible web sources, plus the client sources your team needs. More credible sources are welcome.

Each entry has three parts:

1. The citation in ASCE format. Either place it inside a named footnote, as in the examples below, so it appears under References and can be reused elsewhere on the page with <ref name="Smith2020" />, or write it out in full at the start of the entry. Pick one approach and use it for the whole page.
2. Summary (two to three sentences): what the source is and what it says. Write it in your own words.
3. Relevance (one to two sentences): how it informs this design, e.g., a criterion, a constraint, an alternative, or a decision.

Aim for 75-150 words per entry. No plagiarism: summarize, do not copy. Quote sparingly and always in quotation marks with a citation.

Our client is the Child Development Association student club at Cal Poly Humboldt. The CDA is an organization committed to servicing families, childcare providers, and communities through "innovative solutions and access to essential resources". What matters to them is creating a positive change through innovation and growth and learning shown in their 50th annual report.^[1]

Client interview^[2]

Summary: Meenal Rana who is a professor in the Cal Poly Humboldt Child Development Department and the director of the schools CDA club. Key points were that the device would be interactive for a child to use and learn how to coregulate with a parent/instructor.

Relevance: Device needs to balance its stimulating and regulating components so that children don't get distracted by it. Outer material that is preferably "soft" to the touch that can handle slightly rough use (dropped multiple times). "Breathing" mimicry can be in the form of an ambient glow rather than physical expansion. We also learned how to incorporate a breathing hand movement that they actively teach students into the design of the project.

Client Interview

Client website^[3]

Summary: The CDA is a nonprofit organization that promotes the well-being of families, childcare providers, and the greater community through financial and support services.

Relevance: More information on the CDA and what they believe in.

Client Web

The internal structure of the device will be 3D printed, so the filament type matters as the device is intended for repeated use and should be able to handle the daily abuse of children.

3D Printing Materials Comparison Chart 2026^[4]

Summary: Different filament types vary in specifications and price. Categorized by their printing ease, material strength, toughness, UV resistance, and moisture sensitivity. PLA is great for its ease of use, low moisture absorption, and price, but it isn't good for daily use with children due to its brittleness.^[4] PETG is the best for its high impact strength, which means that it will be good for the structural parts of the orb, and although nylon may be an even better material for our use, its difficulty to work with and high price makes it unsuitable to use as our orb material.

Relevance: The charts^[4] give detailed information on the top 10 most used filaments and compared them side by side. It gives insight for what filament would be best to create the orb out of.

Web

Cast fillers such as epoxy, polyurethane resin, and expanding polyurethane foam can fill empty space inside an interactive children's breathing orb. Cured strength and handling hazards matter for which material gets chosen.

Epoxy resin chemistry and properties^[5]

Summary: Epoxy resins cure into thermoset plastics when mixed with a hardener. A review of how epoxies are made and used explains that resin chemistry and hardener choice control strength, adhesion, heat resistance, and how brittle the cured part is. Compared with soft elastomers and foams, cured epoxy is a stiff structural casting option. Brittleness and leftover uncured chemicals are still the main issues when pouring into molds or cavities.

Relevance: The review gives peer-reviewed property and cure background for comparing epoxy cast fillers with polyurethane and soft-shell options inside a handheld orb.

Peer-reviewed journal

Epoxy skin sensitization outside occupational settings^[6]

Summary: Patch-test evidence shows that contact with bisphenol A–type epoxy resin can sensitize people who are not industrial workers, including hobby and DIY users. Sensitization risk is not limited to factories; it also applies to student shops and home casting. Once someone is sensitized, later skin contact with epoxy can cause dermatitis, so handling rules matter more for any epoxy pour near a child-facing product.

Relevance: The findings support treating epoxy casting as a handling hazard for makers and as a contact concern if uncured residue could reach users of a children's device.

Peer-reviewed journal

Polyurethane foams: chemistry, density, and uses^[7]

Summary: A review of polyurethane foams describes how isocyanate–polyol chemistry makes rigid or flexible foams, and how density and cell structure control mechanical and insulating behavior. Expanding foams can fill irregular cavities and act as cushioning or structural support depending on the mix. That same chemistry means foam and resin processing use reactive chemicals that need controlled mixing and curing.

Relevance: The overview helps evaluate expanding polyurethane foam as an internal filler or drop-absorbing layer inside a hollow breathing-orb shell.

Peer-reviewed journal

Sodium alginate and plaster (gypsum) are useful for prototype molds for casting orb shells and fillers. They are tooling materials, not child-contact materials in the finished product.

Alginate impression materials^[8]

Summary: Alginate impression systems set through an ion-exchange reaction that copies surface detail quickly at low cost. A dental alginate review covers composition, setting behavior, dimensional stability limits, and shelf life. Alginate molds pick up fine geometry but shrink as they dry and are usually single-use. That makes alginate a good fit for fast temporary molds, not durable production tooling.

Relevance: The review clarifies when alginate works for quick skin-safe molds of soft shells or cast fillers, and when shrinkage would hurt geometric accuracy.

Peer-reviewed journal

Setting time of construction and dental gypsum^[9]

Summary: Measured setting times differ among construction gypsum, dental plaster, and white orthodontic gypsum, so mold turnaround depends on which plaster grade is chosen. Faster-setting grades speed up prototype cycles, while slower grades give a longer working window. The study treats set time as a practical mold-making tradeoff, not a fixed property for every plaster.

Relevance: Comparative set times guide plaster selection for lab molds used to form orb shells or cast inserts on a student-lab schedule.

Peer-reviewed journal

USG No. 1 Pottery Plaster mold data^[10]

Summary: Manufacturer technical data for USG No. 1 Pottery Plaster give water-to-plaster ratio guidance, Vicat set times around 14–24 minutes, compressive strength, density, and setting expansion near 0.21%, and they tie mold strength and absorbency to mix ratio (6). Plaster molds therefore come with clear shop numbers for cavity tooling. Extra water weakens the set plaster, while lean mixes stiffen sooner and change how the mold face absorbs moisture.

Relevance: Quantified plaster data support mold design for casting silicone or resin shells where set time, strength, and surface absorbency affect part quality.

Manufacturer technical data

A soft outer shell has to handle squeezing and drops while staying suitable for child contact. That includes any rubberized coating that counts as a surface finish.

Commercial silicone elastomer property mapping^[11]

Summary: Comparative testing of commercial silicone formulations, including common platinum-cure grades such as Sylgard and Ecoflex, maps stiffness, elongation, and related mechanical responses for neat elastomers and blends. Soft grades show high elongation compared with rigid plastics, which fits stretchable shells kids can squeeze by hand. Familiar commercial silicones vary enough that grade choice changes how soft and durable a molded skin feels.

Relevance: Peer-reviewed elastomer data support choosing a platinum-cure silicone Shore hardness and stretch range for a squeezable, translucent breathing-orb shell.

Peer-reviewed journal

Solvent-based rubber coating hazards (Plasti Dip SDS)^[12]

Summary: The safety data sheet for a commercial multi-purpose rubber coating lists aliphatic petroleum distillates, n-hexane, toluene, and methyl ethyl ketone among constituents and documents flammability plus skin, eye, and inhalation hazards during application. Solvent-based dips therefore need ventilation and full solvent flash-off before handling. Residual solvents and fire risk are process downsides compared with addition-cure silicone poured without volatile carriers.

Relevance: The SDS gives handling and ventilation limits for any rubberized dip or brush coating considered as an alternate soft skin on the orb.

Manufacturer safety data sheet

Lead limits for coatings on children's products^[13]

Summary: Federal rules ban paint and similar surface-coating materials that contain lead above 0.009 percent by weight on toys and other children's articles. Any brushed, sprayed, or dipped coating on a child-handled orb falls under surface-coating controls, not only softness criteria. That limits coating chemistry, pigment sources, and supplier paperwork separate from grip or Shore hardness. A coating can feel right and still fail if lead is over the ban threshold.

Relevance: The regulation is a pass/fail constraint on rubberized or painted finishes on a children's interactive product and pairs with soft-shell material choices.

Government web

Shell fabrication choices affect wall uniformity, tooling effort, and how a soft skin bonds to a rigid core. The orb has to glow, flex, and survive handling.

Hand casting soft silicone in additive molds^[14]

Summary: Lab-scale formative manufacturing compares hand casting of soft silicone in fused-filament, stereolithography, and PolyJet-printed molds against injection-style filling, and reports durability, surface quality, and process tradeoffs for soft robotic components.

Advantages: Hand casting in printed molds supports fast geometry changes and low tooling cost for iterative shells, and published benchmarks give selection guidelines among mold processes.

Disadvantages: Surface finish and mold durability vary with the printed mold process, and hand casting can take more labor and skill than closed injection filling for consistent walls.

Peer-reviewed journal

Shop molding, dipping, and coating practice^[15]

Summary: A prop-building reference presents illustrated shop methods for one-part and two-part molds, casting, dipping, brushing, and related coating workflows used to form hollow and solid soft parts.

Advantages: Two-part molds support undercuts and reusable cavity tooling; one-part pour molds stay simple for open shapes; dipping and brushing build thin skins without heavy equipment and suit iterative prop-scale shells.

Disadvantages: Multi-part molds add seam finishing and alignment work, and hand dipping or brushing depends on operator skill for thickness uniformity compared with closed molds or automated processes.

Book

Rotational moulding of hollow parts^[16]

Summary: Industrial rotational moulding tumbles powdered or liquid polymer in a heated closed mold so material coats the cavity and forms seamless hollow parts; process guides cover tooling, materials, and design rules for hollow goods.

Advantages: Rotation favors uniform wall distribution on closed orb-like shapes and can produce seamless hollow shells without cores for some thermoplastics.

Disadvantages: Dedicated rotomolding equipment and heat cycles raise cost and cycle time relative to room-temperature silicone pours, and thermoplastic industrial practice only partly transfers to hand rotocasting of silicones.

Book

Soft-over-rigid adhesion in multi-material printing^[17]

Summary: Experiments on adhesion between fused-filament polylactic acid (PLA) and thermoplastic polyurethane (TPU) show that print parameters, surface pattern, and layer order change bond strength between a rigid core and a soft outer layer.

Advantages: Over molding or co-printing a soft skin onto a printed core can combine grip and structure without separate fasteners when adhesion is strong enough.

Disadvantages: Weak interfaces delaminate under peel or flex, so parameter-sensitive bonding becomes a reliability risk for a shell that gets squeezed repeatedly.

Peer-reviewed Journal

Relevance: Together these sources compare printed-mold silicone casting, shop dipping and coating, rotomolding, and soft-over-rigid over molding so we can weigh wall uniformity, tooling cost, cycle time, and skin-to-core bond strength for a squeezable glowing breathing-orb shell.

Interactive children's products that expand, move, or enclose small parts have to meet mandatory toy safety specifications.

ASTM F963 toy safety specification^[18]

Summary: ASTM F963-23 is the consumer safety specification for toys meant for children under 14. It covers accessible edges and points, small objects, holes and clearances, accessible mechanisms, battery-operated toys, and torque and tension removal tests. The standard ties those design features to lab abuse and accessibility methods. Pinch, choking, battery, and sharp-feature hazards get checked with tests, not just judgment calls.

Relevance: F963 is the main technical specification for pinch points, enclosures, batteries, and abuse resistance on a children's breathing orb.

Safety Standard

Sharp point and sharp edge technical tests^[19]

Summary: 16 CFR 1500.48 and 1500.49 spell out the instruments and accessibility criteria for sharp points and sharp metal or glass edges on toys and articles for children under eight, including after foreseeable damage or abuse. Gear teeth, rack edges, and printed corners that kids can reach can fail these tests. Guarding the mechanism is part of staying clear of sharp-feature failures.

Relevance: These sections apply directly to exposed rack-and-pinion geometry and broken plastic edges inside a child-handled orb.

Government web

Age-related skills and play behaviors^[20]

Summary: CPSC age determination guidelines connect product features to children's physical, cognitive, and play abilities by age, including gripping, prying, and exploring openings and mechanisms. Target age decides which toy rules apply and how hard the abuse and accessibility assumptions should be. That human-factors guidance fills in what pure crush-gap tables miss.

Relevance: Age-band capabilities set realistic assumptions for pinch access, shell prying, and mechanism misuse on a children's orb.

Government web

Shell halves and internal modules have to stay closed under child abuse yet remain serviceable with tools through snap-fits, inserts, press fits, or controlled fasteners.

Snap-fit attachment design^[21]

Summary: A snap-fit handbook covers beam and catch geometry, releasing versus non-releasing locks, constraint management, and troubleshooting for plastic attachments. Non-releasing snaps favor assemblies that kids cannot casually open; releasing features help with intentional service access. The tradeoff is permanence versus being able to service batteries or electronics behind shell halves. Bad constraint stacking makes loose joints or overloaded catches that fail under drop or pry loads.

Relevance: Snap-fit principles guide shell-half and internal-module joints that resist casual opening but still allow tool-assisted service.

Book

Additive-manufactured snap-fit guidelines^[22]

Summary: Design guidelines for additively manufactured snap-fits adapt classic snap rules to layer orientation and anisotropy so printed cantilevers keep strength and can still deflect. When catches bend across layers, print direction is a joint-design choice, not just looks. Ignoring anisotropy risks brittle catch fracture under repeated opening, prying, or drops typical of toys. Guidelines couple CAD catch thickness with build orientation for FFF housings.

Relevance: Printed orb structures that use snaps need orientation-aware joint design to survive handling and regulatory abuse tests.

Peer-reviewed journal

Metal threaded inserts in fused-layer parts^[23]

Summary: Pull-out tests of heat-set metal threaded inserts in thermoplastic fused-layer modelling parts show that infill, wall thickness, layer height, and nozzle temperature change how well inserts hold. Screw joints in printed housings depend on print settings as much as insert size. A weak pull-out lets kids or drops free fasteners.

Relevance: Insert data support tamper-resistant or tool-only screw joints for battery doors and electronics holders in printed orb frames.

Peer-reviewed journal

Electronics, motors, and rack-and-pinion drives need aligned mounts that control vibration, gear mesh, and service access inside the orb.

Small DC motor noise and vibration sources^[24]

Summary: Experiments on small DC motors identify mechanical and electrical sources of noise and vibration across frequency bands. How stiff or soft the mount is affects handheld comfort and how distracting the sound is during paced breathing. Rigid clamping can send vibration into the shell and make more noise at the child's hands. Soft isolation can cut that structure-borne noise if the mount still keeps shaft alignment for the gear train.

Relevance: Motor-noise findings support isolation features in the motor mount of a child-held breathing orb without losing pinion alignment.

Peer-reviewed journal

Machine elements for gears and shafts^[25]

Summary: A machine-elements textbook covers spur-gear geometry, kinematics, and stress concepts, plus shafts, bearings, and fasteners for rotating machinery. Center distance, backlash, and tooth strength decide whether a rack-and-pinion expands smoothly without binding or overloading teeth. Shaft support and fastening also decide how motors and pinions stay aligned under reversing loads. Those fundamentals turn CAD gear sketches into checkable mesh and bearing requirements inside a compact orb.

Relevance: Gear and shaft fundamentals size and align the orb's rack-and-pinion expansion drive and its internal supports.

Book

Dimensional accuracy of FFF printed spur gears^[26]

Summary: Comparative measurements of fused-filament-fabricated spur gears in PLA and nylon show dimensional and form errors that affect mesh quality. Printed gear trains need clearance and alignment adjustment beyond the nominal CAD center distance if binding or too much backlash is going to be avoided. Material choice also changes accuracy and wear of printed pinions under repeated cycling. Form-error results warn against treating printed tooth profiles like molded gears without fit checks.

Relevance: Printed-gear error data inform rack-and-pinion tolerances, shimming, and alignment features inside a 3D-printed orb structure.

Peer-reviewed journal

Prior breathing interfaces and paced-respiration evidence shape how an orb's glow and motion can cue calm, shared breathing for children.

Psycho-physiological effects of slow breathing^[27]

Summary: A systematic review of slow-breathing studies links controlled low-rate respiration to measurable psycho-physiological effects across the reviewed trials. The evidence supports paced breathing as a real regulation strategy, not just a wellness-product design idea. Glow or motion rhythms that invite slow inhale and exhale can rest on those documented responses. Rate choice for an orb cue can be based on that slow-breathing evidence.

Relevance: The review supports slow expansion or light pacing as a breathing cue for a calm-down children's interactive device.

Peer-reviewed journal

Guided audiovisual paced breathing for children^[28]

Summary: A pilot randomized controlled trial tests a guided paced-breathing audiovisual intervention with Palestinian children about six to ten years old and reports effects on anxiety symptoms. Visual pacing already has evidence with school-age children, not only adult office workers. Results support child-facing visual guides, including light or motion cues, instead of leaning only on adult biofeedback ideas. The trial also stresses age-appropriate pacing content and delivery.

Relevance: Child-specific paced-breathing evidence informs an orb that uses light or motion as a visual breathing guide for young users.

Peer-reviewed journal

ChillFish tangible respiration game^[29]

Summary: ChillFish is a tangible, fish-shaped respiration game where children with ADHD breathe into a physical controller to drive calming play. The TEI paper shows a handheld breathing object tied to interactive feedback, so physical form can carry breathing tasks for kids instead of screen-only exercises. That tangible approach is similar to an orb children hold while matching a paced cue. Existing similar solutions include graspable controllers that turn breathing into game state.

Relevance: ChillFish is a close existing-solution precedent for a child-oriented physical breathing device with interactive feedback.

Peer-reviewed Journal

Shared breathing biofeedback between partners^[30]

Summary: Breeze shares one person's breathing with a partner through wearable light, vibration, and sound so two users can synchronize or watch respiration together. That gives multi-user biofeedback an interface precedent beyond single-user pacing displays. Shared cues fit cooperative parent–child or peer breathing goals for a dual-user orb. Light and haptic channels in the CHI study show how one partner's breath can become the other's ambient guide.

Relevance: Partnered breathing feedback supports literature grounding for a cooperative, multi-user breathing orb with shared sensory cues.

Peer-reviewed Journal

Selecting an appropriate microcontroller is important because the installation must process two user inputs and produce accurate, immediate visual and/or haptic feedback.^[2]

Possible controller platforms include Arduino development boards, ESP32 microcontrollers, Raspberry Pi Pico boards, and generic microcontrollers such as AVR, PIC, or STM32 devices.^{[31][32][33][34]} A full-sized Raspberry Pi is a Linux-based single-board computer rather than a microcontroller, so it would have different power, startup, and programming requirements

Embedded Systems: Real-Time Interfacing to ARM Cortex-M Microcontrollers^[31]

Summary: Microcontrollers combine a processor, memory, and input/output peripherals into a compact embedded computing system. Simpler 8-bit and 16-bit controllers are commonly used for basic sensing and control, while 32-bit controllers provide greater processing capacity for filtering sensor data, coordinating wireless communication, and operating several outputs. Valvano also describes analog-to-digital conversion, interrupts, timers, pulse-width modulation, data collection, and communication interfaces.

Relevance: These concepts establish the features needed to compare controller alternatives for the breathing installation. The selected controller must read both users’ sensors, calculate their level of synchronization, and update lights or vibration with minimal delay.

Book

ESP32-S3 Series Datasheet^[32]

Summary: The ESP32-S3 is a 32-bit, dual-core microcontroller system-on-chip with integrated 2.4-GHz Wi-Fi and Bluetooth Low Energy. It provides analog-to-digital conversion, timers, pulse counters, LED pulse-width modulation, and communication interfaces including I²C, SPI, and UART.

Relevance: The ESP32-S3’s inputs and outputs could support breathing sensors, indicator lights, and motor-control electronics. Its integrated Bluetooth and Wi-Fi also allow separate handles or modules to exchange data without adding a separate wireless controller.

Credible web source

Arduino UNO R4 WiFi^[33]

Summary: The Arduino UNO R4 WiFi is a development board containing a 32-bit Renesas RA4M1 microcontroller and a separate ESP32-S3 module for Wi-Fi and Bluetooth communication. The primary controller includes digital and analog input/output pins, timers, memory, a digital-to-analog converter, and a real-time clock. Arduino also provides programming libraries, example programs, and documentation for connecting common sensors and output devices.

Relevance: The Arduino platform provides an accessible method for prototyping sensor inputs, light controls, and motor feedback. Its existing libraries and documentation could simplify development, although using separate primary and wireless processors may affect programming and hardware organization.

Credible web source

Raspberry Pi Pico Microcontroller Boards^[34]

Summary: Raspberry Pi Pico boards use either the RP2040 or RP2350 microcontroller and can be programmed using MicroPython, C, or C++. They provide programmable digital pins, analog inputs, timers, pulse-width modulation, USB support, and low-power operating modes. Wireless models identified with a “W,” such as the Pico W and Pico 2 W, also include Wi-Fi and Bluetooth capabilities. Unlike a full-sized Raspberry Pi, a Pico does not run the Linux operating system.

Relevance: The Pico platform provides another compact option for reading breathing sensors and controlling feedback. Its programming-language choices, input/output capability, wireless versions, and low-power features provide useful comparison points against the ESP32 and Arduino alternatives.

Credible web source

The controller’s code must convert raw sensor measurements into dependable feedback by identifying breathing cycles, comparing the timing of two users, and responding safely when measurements are missing or unreliable.^[31][35][36]

Pediatric Respiratory Monitoring^[35]

Summary: Seebauer et al. evaluated a contactless breathing-monitoring system with 27 pediatric participants ranging from infants to older children. The system used a depth-sensing camera to measure chest and abdominal movement, while its software applied a moving-average filter to reduce motion artifacts and detected respiratory cycles from the filtered signal. The measurements were compared with standard clinical sleep-monitoring equipment.

Relevance: This study shows that a child-centered breathing device should minimize discomfort and account for movement, noise, body position, and inconsistent sensor signals. Because the study primarily analyzed children while they were sleeping and relatively still, additional testing would be necessary for an interactive classroom device used by children who may move while breathing.

Peer-reviewed journal article

ESP32-S3 Watchdog Timers^[36]

Summary: Espressif’s programming documentation describes watchdog timers that monitor whether software tasks and interrupt routines execute within an expected amount of time. The ESP32-S3 includes interrupt, task, real-time-clock, and crystal watchdog functions. If part of the program remains blocked or fails to run normally, a watchdog can create an error event or reset the controller instead of allowing it to remain unresponsive.

Relevance: Watchdog timers could help prevent the breathing installation from freezing with lights or vibration stuck in an incorrect state. This source also supports evaluating software timeouts for disconnected sensors, invalid measurements, and other conditions that interrupt normal feedback.

Credible web source

Motorized feedback lets the device add controlled pushback or help so breathing motion feels guided.

Haptic device design handbook^[37]

Summary: This open-access book explains how to build devices that create force and touch feedback people can feel. It covers motors, sensors, control methods, and safety when a person pushes on the device. The editors also discuss how a drive should feel transparent when the user leads the motion and stable when the device leads or resists. Chapters address common actuator choices and why human-in-the-loop systems need careful power and control limits.

Relevance: It helps set goals for motorized breathing resistance that feels controlled and safe for a child and caregiver. The book supports treating the orb path as a haptic channel, not only as a free-spinning motor demo, and it backs criteria for adjustable resistance without trapping the user’s hands.

Book

Electromagnetic brake for haptic resistance^[38]

Summary: This journal paper describes an electromagnetic brake made for haptic interfaces. The brake adds adjustable opposing torque without using only the drive motor. The authors explain a bilayer multipole layout meant to give smoother, more controllable braking for force feedback. Their tests show variable resistance that can change with current instead of relying on heavy gearing alone.

Relevance: It shows a way to add smooth breathing resistance with a separate brake instead of only reversing the main motor. That option informs criteria for gentle, tunable pushback on the orb while keeping the main drive simpler and easier to backdrive when the brake is off.

Peer-reviewed journal

Dry-friction stick-slip simulation^[39]

Summary: This journal paper models dry friction that sticks, then slips, under changing load. It shows how friction alone can hold and release motion in a mechanism. The stick-slip behavior creates periods of no motion followed by sudden slip, which can feel rough or jerky compared with smoothly controlled motor torque. The authors use numerical simulation of Coulomb friction to study constrained systems where friction is the main opposing force.

Relevance: It helps compare rough mechanical drag with smoother motor-controlled resistance on the orb path. The paper supports deciding whether a simple friction pad is acceptable for breathing guidance or whether motor or electromagnetic braking is needed for a steadier feel.

Peer-reviewed journal

H-bridge motor driver braking modes^[40]

Summary: This datasheet covers a small dual H-bridge motor driver. It lists drive, coast, and brake modes and ways to limit motor current and torque. In brake mode the windings can be shorted so the motor resists motion electrically; in coast mode the motor spins more freely. Current limiting is described so peak torque stays within safe hardware limits for small DC motors.

Relevance: It shows how electronics can create adjustable motor resistance for the breathing drive without a separate brake. The modes support criteria for soft stop, holding feel, and limited opposing torque when a child or caregiver moves the orb by hand.

Web

Backdrivability and gearing decide whether a person can still move the mechanism by hand when the motor is off or lightly powered.

Actuator backdrivability factors^[41]

Summary: This journal paper reviews what makes a robotic actuator easy or hard to push backward by hand. It covers gearing, friction, inertia, and motor choices that change how transparent a drive feels. High reduction gears often raise output torque but also raise reflected inertia and friction, which can make hand motion feel locked or heavy. The authors organize these factors for human-centered robots where people share the workspace with powered joints.

Relevance: It helps choose a breathing drive that stays movable and safe instead of locking up under high gear reduction. The paper backs a design requirement that the orb mechanism remain backdrivable so users can finish a breath motion even if motor power drops.

Peer-reviewed journal

Motor and gearing selection guide^[42]

Summary: This university lab page explains how to pick a motor and gear ratio for a mechanism. It covers torque, speed, and the tradeoff between power and how hard the output is to turn by hand. The guide walks through matching load torque and desired speed to a motor curve and then selecting reduction. It also notes that more gearing is not always better when people must move the output.

Relevance: It supports sizing the orb drive so it can move under load without becoming too stiff for a child or caregiver to backdrive. The page is a practical checklist for early motor and gearbox choices before buying parts.

Web

Hall sensors read magnetic fields and can tell when a magnet puck is seated under the orb.

Hall effect sensor datasheet guide^[43]

Summary: This Texas Instruments note explains how to read Hall effect sensor datasheets. It covers output types, sensing range, and how magnetic field strength maps to a usable signal. It distinguishes switching digital Halls from linear Halls that output a variable voltage with field strength. The note also flags package, supply, and magnetic operating point details that affect reliable detection.

Relevance: It supports using Hall sensors to detect a magnet puck pattern and unlock or set control modes without metal contacts. Linear Halls are especially relevant if the team wants a graded reading of puck seating rather than a simple on/off switch.

Web

Wireless links connect the breathing interface to a controller or companion device over short range.

Bluetooth technology overview^[44]

Summary: This Bluetooth SIG page summarizes how Bluetooth works for short-range wireless links. It covers common uses, range expectations, and why it is widely used for small connected devices. Bluetooth is aimed at personal-area links rather than long-distance radio, which fits a device used next to a phone, tablet, or classroom controller. The overview also frames Bluetooth as a standard many consumer devices already support.

Relevance: It helps evaluate Bluetooth as a simple wireless option between the breathing device and a phone, tablet, or controller in a classroom or clinic setting. It supports criteria for short-range pairing without building a custom radio protocol from scratch.

Web

FCC Part 15 unlicensed radio rules^[45]

Summary: This FCC rule section lists limits for unlicensed radios in common bands such as 2.4 GHz. It explains what low-power devices must meet to operate without an individual license. Field strength and operating band limits are given so designers know the legal envelope for Part 15 gear. The rule is a compliance reference, not a product tutorial, but it defines what unlicensed classroom devices must stay within.

Relevance: It supports choosing a legal, low-power wireless design for the breathing system in a public or campus setting. It backs a constraint that any radio module or custom link must remain within Part 15 limits for unlicensed use.

Web

• Device needs a soft, drop-tolerant outer shell and a calm breathing cue (glow or slow motion) so kids can co-regulate with a parent or instructor without getting overstimulated. Soft platinum-cure silicone fits that better than solvent rubber coatings that need heavy ventilation and have lead limits on kids’ products. ^{[2][11][12][13][27][28]}
• Internal structure will be 3D printed, so filament choice matters for daily kid use, and any epoxy, polyurethane resin, or expanding foam filler has to fully cure and stay sealed away from skin. Shell options (printed-mold casting, dipping/coating, rotomolding, soft-over-rigid print) should be picked for wall evenness, tooling cost, and whether a soft skin stays bonded when squeezed. ^{[4][5][6][7][8][9][10][14][15][16][17]}
• Toy safety is a hard constraint. ASTM F963, sharp point/edge rules, and age-based play behavior mean gears, racks, batteries, and fasteners have to stay enclosed and survive drop/pry abuse. Snap-fits and heat-set inserts have to hold so parts do not come loose as small-part hazards.^{[18][19][20][21][22]}
• The controller has to read two users, drive lights or haptics with little delay, and recover if a sensor drops out. ESP32-S3, Arduino UNO R4 WiFi, and Pico are all workable platforms; Valvano’s embedded concepts and ESP32 watchdogs support safe timing and fail-safe resets.^{[2][31][32][33][34][35][36]}
• Similar products and research back a handheld cooperative design: ChillFish and Breeze show tangible and shared breathing feedback, Hall sensors can ID a magnet puck for modes, and Bluetooth under FCC Part 15 covers short-range wireless between modules in a classroom setting.^{[29][30][43][44] [45]}

Introduce this section in one to two sentences specific to your project.

Describe four to eight alternatives, each under its own 'step template' as shown below and each with a catchy, descriptive name.

I could not figure out how to add images to thee templates. will ask in class.

Continue this for the four to eight alternatives you have.

Introduce this section in one to two sentences specific to your project.

Define each criterion from Table 1 as it is used to judge the alternatives. These are definitions, not constraints. For example, the constraint on cost is the budget, but cost might be defined as the cost of materials only, or as materials plus operation and maintenance. If your criteria changed, update Table 1 so the two match.

Cost

Definition...

Taste

Definition...

Explain the decision process your team used (e.g., decision matrix, Pugh chart). First person is appropriate here. Refer to the table, e.g., Table 2 summarizes the decision matrix.

Table 2: Decision matrix. Scores are 0-10; weighted totals are the sum of weight × score.

Criterion	Weight	Alternative A	Alternative B	Alternative C
Cost	10	7	5	9
Taste	7	8	9	4
Weighted total		126	113	118

Name the chosen solution and justify it with reference to the criteria and Table 2.

Show your most impactful prototypes from earliest to final. Include at least one prototype for function (does it work? e.g., testing a mechanism, material, or dimension) and at least one prototype for desire (will people want to use it? e.g., a mockup shown to the client or users for feedback). Each caption should say what the prototype is, whether it tested function or desire, and what you learned from it. Early sketches, failed attempts, and photos of materials and hands at work all help tell the story.

• 
  Prototype for desire: cardboard mockup of ... shown to the client. We learned that ...
• 
  Prototype for function: test of ... We learned that ...

Describe the final design, starting with the big picture and then going into detail. Use labeled images and refer to them in the text. This is usually a big section.

• 
  CAD drawing of ... by Yourname1.
• 
  Drawing of ... by Yourname2.

Give a complete description of how the final design is built, with lots of images, so someone else could replicate it. Use one {{Step}} per step. This is much easier to write as descriptive (what you did) instead of prescriptive (what another person should do), but you can take either approach.

This timeline shows our proposed goals for progress on this project. We plan to fully understand the design of our project by October 9th, complete our first prototype by October 30th, finish adjusting functionality by November 13th, and finalize aesthetics and presentation by December 18th.

Table 3: Project timeline.

Date	Description	Status
October 9, 2026	Complete research and finalize product plan	In progress
October 30, 2026	First prototype completed	Not started
November 13, 2026	Completion of testing and adjusting functionality	Not started
November 27, 2026	Finalizing product	Not started
December 4, 2026	Ambitious goals and aesthetics	Not started
December 18, 2026	Project and presentation completion	Not started

Introduce the three kinds of cost below in one to two sentences.

Show the total human hours your team spent outside of class, grouped into categories (e.g., research, brainstorming, prototyping, construction, documentation). Three teammates working for one hour is three human hours.

Introduce the costs to build the design, including donations and reused materials. Note whether costs are actual or proposed. If replication would cost a different amount, say so.

Item	Amount	Cost per unit	Total
Thing - from the thing store — Purchased	3	USD 5.75	USD 17.25
Another thing - 3' x 2', yellow — Donated by ...	1	USD 0.00	USD 0.00
PrintGrand total			USD 17.25EUR 14.84 <br />GBP 12.59 <br />CAD 21.39 <br />MXN 359.66 <br />INR 1,291.16 <br />

Introduce the ongoing costs in time and money, usually per year.

Table 4: Yearly maintenance cost.

Task	Frequency	Time per year (hours)	Cost per year (USD)
Example task	Monthly	2	0.00
Total		2	0.00

Introduce how to use the design, then give step-by-step instructions with labeled images. Use {{Step}} if the process has more than a few steps. A short video is a great addition:

Introduce this maintenance section. Answer these questions:

• Are there any needed actions for maintenance?
• How often?
• Who should perform maintenance?

This is when to maintain what. Please keep the format the same as it can be used to auto-populate maintenance tables.

Daily

• A daily task
• A daily task

Weekly

• a weekly task
• a weekly task

Monthly

• a monthly task
• a monthly task

Yearly

• a yearly task
• a yearly task

Every __ years

• task
• task

Give step-by-step maintenance instructions, using {{Step}} if helpful.

Describe how you tested the final design and what the results were. Compare the results to your criteria, e.g., in a table like Table 5.

Table 5: Final design performance against criteria.

Criterion	Constraint	Result	Met?
Cost	Less than or equal to $3 per ounce	$2.50 per ounce	Yes

Discuss what the testing results mean.

Discuss what your team learned and what you would do differently next time.

Discuss next steps for the project as it goes on into the future.

Cover basic operating problems only. For complex issues, the suggestion might be to contact ________.

Problem	Suggestion
Example issue	Example solution or suggestion
Does not turn on	Make sure it is plugged in.
Another issue	Etc.

Include an inspirational video for sharing.

Introduce the team and semester, e.g., This project was completed in SEMESTER YEAR by Team TEAMNAME:

• Lonny Grafman
• Emilio Velis
• One bullet for each team member, in the format [[User:Username|Full Name]].

1. ↑ Richardson, R. (2025). “50 years of impact - our 2024 annual report is here.” <https://cdasd.org/news/50-years-of-impact-our-2024-annual-report-is-here/> (Sep. 24, 2026).
2. ↑ ^{2.0 2.1 2.2 2.3} Rana, M. (2026). “Interview concerning the cooperative breathing installation.” by BBB, Sept. 18, 2026, Arcata, CA.Menal. (2026).
3. ↑ Child Development Association. (2026). “We create positive change.” (n.d.). <https://cdasd.org/> (Sep. 24, 2026).
4. ↑ ^{4.0 4.1 4.2 4.3} “3D printing materials comparison chart 2026 (printable + free PDF).” (2026). CovertItAll, <https://covertitall.com/printables/filament-comparison-chart.html> (Sep. 25, 2026).
5. ↑ ^{5.0 5.1} Jin, F.-L., Li, X., and Park, S.-J. (2015). "Synthesis and application of epoxy resins: A review." Journal of Industrial and Engineering Chemistry, 29, 1–11. https://doi.org/10.1016/j.jiec.2015.03.026
6. ↑ ^{6.0 6.1} Majasuo, S., Liippo, J., and Lammintausta, K. (2012). "Non-occupational contact sensitization to epoxy resin of bisphenol A among general dermatology patients." Contact Dermatitis, 66(3), 148–153. https://doi.org/10.1111/j.1600-0536.2011.01993.x
7. ↑ ^{7.0 7.1} Gama, N. V., Ferreira, A., and Barros-Timmons, A. (2018). "Polyurethane foams: Past, present, and future." Materials, 11(10), 1841. https://doi.org/10.3390/ma11101841
8. ↑ ^{8.0 8.1} Cervino, G., Fiorillo, L., Herford, A. S., Laino, L., Troiano, G., Amoroso, G., Crimi, S., Matarese, M., D'Amico, C., Nastro Siniscalchi, E., and Cicciù, M. (2019). "Alginate materials and dental impression technique: A current state of the art and application to dental practice." Marine Drugs, 17(1), 18. https://doi.org/10.3390/md17010018
9. ↑ ^{9.0 9.1} Darmawan, I., Willy, O., and Budiman, J. A. (2020). "Setting time of construction gypsum, dental plaster, and white orthodontic gypsum." Journal of Dental Research, Dental Clinics, Dental Prospects, 14(3), 167–170. https://doi.org/10.34172/joddd.2020.036
10. ↑ ^{10.0 10.1} USG Corporation. (2017). "USG No. 1 Pottery Plaster" (data sheet IG1366, rev. 9-17). USG, https://www.usg.com/content/dam/USG/pdpmovedocuments/usg-no1-pottery-plaster-data-en-IG1366.pdf (Sep. 26, 2026).
11. ↑ ^{11.0 11.1} Vaicekauskaite, J., Mazurek, P., Vudayagiri, S., and Skov, A. L. (2020). "Mapping the mechanical and electrical properties of commercial silicone elastomer formulations for stretchable transducers." Journal of Materials Chemistry C, 8(4), 1273–1279. https://doi.org/10.1039/c9tc05072h
12. ↑ ^{12.0 12.1} Plasti Dip International. (2018). "Safety data sheet: 14.5oz PD Black" (product code 11603-6, version 15, revised Mar. 9, 2018). Hosted by TAP Plastics, https://www.tapplastics.com/image/pdf/SDS-11603-6.pdf (Sep. 26, 2026).
13. ↑ ^{13.0 13.1} U.S. Consumer Product Safety Commission (CPSC). (2026e). "16 CFR Part 1303 – Ban of lead-containing paint and certain consumer products bearing lead-containing paint." Electronic Code of Federal Regulations, https://www.ecfr.gov/current/title-16/chapter-II/subchapter-B/part-1303 (Sep. 26, 2026).
14. ↑ ^{14.0 14.1} Folinus, C. M., Massimino, D., Arase, C., and Becker, K. P. (2026). "Lab-scale fabrication process selection for soft robotics: Benchmarking, tradeoffs, and guidelines for formative manufacturing of soft silicone components." Advanced Intelligent Systems, e70519. https://doi.org/10.1002/aisy.70519
15. ↑ ^{15.0 15.1} Hart, E. (2023). The prop building guidebook: For theatre, film, and TV, 3rd Ed., Routledge, New York. https://doi.org/10.4324/9781003244240
16. ↑ ^{16.0 16.1} Crawford, R. J., and Kearns, M. P. (2021). Practical guide to rotational moulding, 3rd Ed., Elsevier, Amsterdam.
17. ↑ ^{17.0 17.1} Brancewicz-Steinmetz, E., Sawicki, J., and Byczkowska, P. (2021). "The influence of 3D printing parameters on adhesion between polylactic acid (PLA) and thermoplastic polyurethane (TPU)." Materials, 14(21), 6464. https://doi.org/10.3390/ma14216464
18. ↑ ^{18.0 18.1} ASTM International. (2023). Standard consumer safety specification for toy safety, ASTM F963-23, ASTM International, West Conshohocken, PA. https://doi.org/10.1520/F0963-23
19. ↑ ^{19.0 19.1} U.S. Consumer Product Safety Commission (CPSC). (2026a). "16 CFR 1500.48 – Technical requirements for determining a sharp point in toys and other articles intended for use by children under 8 years of age"; and (2026b) "16 CFR 1500.49 – Technical requirements for determining a sharp metal or glass edge in toys and other articles intended for use by children under 8 years of age." Electronic Code of Federal Regulations, https://www.ecfr.gov/current/title-16/chapter-II/subchapter-C/part-1500/section-1500.48 and https://www.ecfr.gov/current/title-16/chapter-II/subchapter-C/part-1500/section-1500.49 (Sep. 26, 2026).
20. ↑ ^{20.0 20.1} U.S. Consumer Product Safety Commission (CPSC). (2020). "Age determination guidelines: Relating consumer product characteristics to the skills, play behaviors, and interests of children." CPSC.gov, https://www.cpsc.gov/content/2020-Age-Determination-Guidelines (Sep. 26, 2026).
21. ↑ ^{21.0 21.1} Bonenberger, P. R. (2016). The first snap-fit handbook: Creating and managing attachments for plastics parts, 3rd Ed., Hanser, Munich. https://doi.org/10.3139/9781569905968
22. ↑ ^{22.0 22.1} Klahn, C., Singer, D., and Meboldt, M. (2016). "Design guidelines for additive manufactured snap-fit joints." Procedia CIRP, 50, 264–269. https://doi.org/10.1016/j.procir.2016.04.130
23. ↑ Kastner, T., Troschitz, J., Vogel, C., Behnisch, T., Gude, M., and Modler, N. (2023). "Investigation of the pull-out behaviour of metal threaded inserts in thermoplastic fused-layer modelling (FLM) components." Journal of Manufacturing and Materials Processing, 7(1), 42. https://doi.org/10.3390/jmmp7010042
24. ↑ Cho, Y. T. (2018). "Characterizing sources of small DC motor noise and vibration." Micromachines, 9(2), 84. https://doi.org/10.3390/mi9020084
25. ↑ Mott, R. L., Vavrek, E. M., and Wang, J. (2018). Machine elements in mechanical design, 6th Ed., Pearson, New York.
26. ↑ Buj-Corral, I., and Zayas-Figueras, E. E. (2023). "Comparative study about dimensional accuracy and form errors of FFF printed spur gears using PLA and Nylon." Polymer Testing, 117, 107862. https://doi.org/10.1016/j.polymertesting.2022.107862
27. ↑ ^{27.0 27.1} Zaccaro, A., Piarulli, A., Laurino, M., Garbella, E., Menicucci, D., Neri, B., and Gemignani, A. (2018). "How breath-control can change your life: A systematic review on psycho-physiological correlates of slow breathing." Frontiers in Human Neuroscience, 12, 353. https://doi.org/10.3389/fnhum.2018.00353
28. ↑ ^{28.0 28.1} Shank, L. M., Grace, V., Delgado, J., Batchelor, P., de Raadt St James, A., Sundaresan, A., and Bouchedid, L. (2023). "The impact of a guided paced breathing audiovisual intervention on anxiety symptoms in Palestinian children: A pilot randomized controlled trial." Child and Adolescent Mental Health, 28(4), 473–480. https://doi.org/10.1111/camh.12613
29. ↑ ^{29.0 29.1} Sonne, T., and Jensen, M. M. (2016). "ChillFish: A respiration game for children with ADHD." Proc., 10th Int. Conf. on Tangible, Embedded, and Embodied Interaction (TEI '16), ACM, New York, 271–278. https://doi.org/10.1145/2839462.2839480
30. ↑ ^{30.0 30.1} Frey, J., Grabli, M., Slyper, R., and Cauchard, J. R. (2018). "Breeze: Sharing biofeedback through wearable technologies." Proc., 2018 CHI Conf. on Human Factors in Computing Systems, ACM, New York, 1–12. https://doi.org/10.1145/3173574.3174219
31. ↑ ^{31.0 31.1 31.2 31.3} Valvano, J.W. (2011). Embedded Systems: Real-Time Interfacing to ARM Cortex-M Microcontrollers, 3rd Ed., CreateSpace Independent Publishing Platform, North Charleston, SC.
32. ↑ ^{32.0 32.1 32.2} Espressif Systems. (2026a). “ESP32-S3 Series Datasheet, Version 2.2.” Espressif Systems https://documentation.espressif.com/esp32-s3_datasheet_en.pdf. (September 27, 2026).
33. ↑ ^{33.0 33.1 33.2} Arduino. (n.d.). “UNO R4 WiFi.” https://docs.arduino.cc/hardware/uno-r4-wifi (accessed September 27, 2026).
34. ↑ ^{34.0 34.1 34.2} Raspberry Pi Ltd. (n.d.). “Pico microcontroller boards.” https://www.raspberrypi.com/documentation/microcontrollers/pico-series.html (accessed September 27, 2026).
35. ↑ ^{35.0 35.1 35.2} Seebauer, L. M., Geis, M., Köhler, N. A., Nöh, C., Frey, J., Groß, V., Sohrabi, K., and Kerzel, S. (2026). “Clinical evaluation of an AI-based prototype for contactless respiratory monitoring in children.” Children, 13(2), 232. https://doi.org/10.3390/children13020232.
36. ↑ ^{36.0 36.1 36.2} Espressif Systems. (2026). “Watchdogs—ESP32-S3.” ESP-IDF Programming Guide, https://docs.espressif.com/projects/esp-idf/en/release-v6.0/esp32s3/api-reference/system/wdts.html (accessed September 27, 2026).
37. ↑ Kern, T. A., C. Hatzfeld, and A. Abbasimoshaei, eds. 2023. Engineering haptic devices. 3rd ed. Cham, Switzerland: Springer. https://doi.org/10.1007/978-3-031-04536-3
38. ↑ Iqbal, H., and B.-J. Yi. 2019. Design of a new bilayer multipole electromagnetic brake system for a haptic interface. Appl. Sci. 9 (24): 5394. https://doi.org/10.3390/app9245394
39. ↑ He, B., S. Pan, Z. Zhang, Y. Mei, and W. Zhang. 2026. Numerical simulation of the dry friction constrained system based on Coulomb stick-slip motion. Symmetry 18 (1): 57. https://doi.org/10.3390/sym18010057
40. ↑ Texas Instruments. 2015. DRV8833 Dual H-Bridge Motor Driver. Data Sheet SLVSAR1E (rev. July 2015). Dallas: Texas Instruments. Accessed September 27, 2026. https://www.ti.com/lit/ds/symlink/drv8833.pdf
41. ↑ Texas Instruments. 2015. DRV8833 Dual H-Bridge Motor Driver. Data Sheet SLVSAR1E (rev. July 2015). Dallas: Texas Instruments. Accessed September 27, 2026. https://www.ti.com/lit/ds/symlink/drv8833.pdf
42. ↑ Northwestern University Mechatronics Design Lab. n.d. Choosing a motor and gearing combination. Northwestern University Mechatronics Wiki (HADES). Accessed September 27, 2026.
43. ↑ ^{43.0 43.1} Eisenbeis, R. 2021. Understanding and applying Hall effect sensor data sheets. Application Report SLIA086A. Dallas: Texas Instruments. Accessed September 27, 2026. https://www.ti.com/lit/an/slia086a/slia086a.pdf
44. ↑ ^{44.0 44.1} Bluetooth SIG. n.d. Bluetooth technology overview. Bluetooth. Accessed September 24, 2026. https://www.bluetooth.com/learn-about-bluetooth/tech-overview/
45. ↑ ^{45.0 45.1} FCC (Federal Communications Commission). n.d. §15.249 Operation within the bands 902–928 MHz, 2400–2483.5 MHz, 5725–5875 MHz, and 24.0–24.25 GHz. Electronic Code of Federal Regulations. Accessed September 24, 2026. https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-C/section-15.249