My Final Project
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My final project is a wearable exoskeleton designed to assist in the rehabilitation of people with limited finger mobility. The main goal is to help users open and close their hand using a mechanical system controlled by buttons.
The device works as follows:
- Pressing one button will close the fingers.
- Pressing another button will open the fingers.
- A third button will return the hand to a neutral position.
The mechanism is based on a tension system using strings connected to servomotors. When the motor rotates, it pulls the string, causing the fingers to move—similar to how tendons function. The goal is to create a device that is both functional and comfortable for the user.
Below are some of the initial design ideas. While I explored different options, I based the final prototype mostly on the second sketch, as it offers a better balance between functionality and comfort.
Research
My design inspiration came mainly from the GrippLyfe glove, a robotic rehabilitation glove designed to assist hand movement, especially in patients with paralysis or muscle weakness. It works through soft pneumatic actuators that inflate with compressed air to flex the fingers in a controlled way. These actuators are connected to an air pump and solenoid valves that regulate the flow to each finger, controlled by a microcontroller. The system allows for smooth and safe movements, mimicking natural muscle function, and can be used in mirror mode to replicate the healthy hand's movements in the affected hand as part of active rehabilitation therapy.
My design idea is to replicate that movement, but instead of using pneumatic actuators, I will use servomotors. These will be placed inside the arm, along with a wristband that attaches to the forearm. This is where I will place the board I designed in Week 8. I will discuss the board and its function later. The motors and the necessary buttons will also be there.
The device will function as a robotic glove or exoskeleton worn on the affected hand, designed to assist in movement and rehabilitation. It will use motorized actuators to mimic natural finger motion.
Hand Anatomy and Movement
The following images show the bones and movements of the hand:
Materials and Components
🔩 Electronics and Mechanical Components
| Component | Supplier / Link | Approx. Cost (MXN) | Approx. Cost (USD) | Notes |
|---|---|---|---|---|
| TPU Filament 1.75 mm (1 kg) | MercadoLibre | $320.00 | $17.78 | Flexible material for 3D printing the exoskeleton |
| Nylon Thread 0.60 mm (100 m) | MercadoLibre | $62.00 | $3.44 | Used as tendon for finger movement |
| AMS1117-5V Voltage Regulators (10 pcs) | MercadoLibre | $49.00 | $2.72 | Only a few units used |
| AMS1117-3.3V Voltage Regulators (10 pcs) | MercadoLibre | $49.00 | $2.72 | Only a few units used |
| 4 MG995 Servo Motor | MercadoLibre | $89.00 | $4.94 | High torque, ideal for finger movement |
| Female Header 40 pins (10 pcs) | MercadoLibre | $39.00 | $2.17 | For interconnecting modules |
| Male Header 36 pins | Steren | $15.00 | $0.83 | For soldering to circuit board |
| Phenolic Board 10x15 cm | Steren | $24.00 | $1.33 | Used for manual circuit assembly |
| 60/40 Tin-Lead Solder (17 g) | Steren | $25.00 | $1.39 | For soldering components |
🧰 Components Provided by the FabLab Ibero Puebla (Free of Charge)
| Component | Quantity / Use | Cost (MXN) | Cost (USD) | Notes |
|---|---|---|---|---|
| Xiao RP2040 | 1 unit | $0.00 | $0.00 | Main microcontroller |
| 4.7µF SMD Capacitors | Several | $0.00 | $0.00 | Used for voltage filtering |
| SMD PushButtons | Several | $0.00 | $0.00 | Used for user interaction |
💰 Total Estimated Cost
Purchased Components Total: $787.00 MXN (~$43.72 USD)
FabLab Provided Components: $0.00 MXN / $0.00 USD
Project Timeline
This timeline outlines the weekly tasks and milestones to complete the assistive exoskeleton for three fingers (thumb, index, and middle) using voice control and servomotors.
| Date | Task | Goal |
|---|---|---|
| May 13 – May 19 | Finalize design sketches, 3D model phalanges in SolidWorks | Have all CAD designs ready for printing |
| May 20 – May 26 | 3D print all components and test joint fit | Have functional mechanical finger structures |
| May 27 – June 2 | Assemble the system with servos, mount cables | Have a full working prototype structure |
| June 3 – June 5 | Integrate voice control and finalize code | Device responds to commands like "open" and "close" |
| June 6 – June 9 | Testing, adjustments, and final documentation | Prepare for final presentation and review |
Control Methods:
- Voice commands: The user can control the device using simple commands like "open" and "close"
- Button interface: A push-button will be available for users who prefer manual operation.
Key Features:
- Grip Assistance
- Rehabilitation Exercises
- Wearable & Lightweight
Materials & Components
The following tables outline the components used in my final rehabilitation exoskeleton project, categorized by mechanical structure, external electronics, and components used in my custom PCB.
3.1 Mechanical Components
| Item | Details |
|---|---|
| TPU Filament | (for flexible parts and cushioning) |
| M3 Screws & Nuts | Various lengths and quantities (TBD) |
| Velcro Straps | For adjusting and securing the exoskeleton |
| Tension Cable | 1/8" for the tensioning mechanisms |
| Supports and Plates | Base plate, motor supports, and anchors (3D printed) |
3.2 External Electronics Components
| Component | Quantity |
|---|---|
| SG90 or MG995 Servo Motors | 5 units |
| Xiao ESP32C3 Microcontroller | 1 unit |
| 5V External Power Source | 1 unit (for servos) |
| Prototyping Board | 1 unit |
| Dupont Cables | Assorted |
| Power Switch | 1 unit |
| Control Button | 1 unit (for manual motor control) |
| LED (Motor Active Indicator) | 1 unit |
| LED (Bluetooth Connection Indicator) | 1 unit |
3.3 Custom PCB Components
| Component | Specification / Package | Quantity |
|---|---|---|
| XIAO RP2040 | — | 1 |
| SG90 or MG995 Servo Motors | — | 5 |
| Resistor | 220Ω (for LED) | 2 |
| Resistor | 10kΩ (for button pull-down) | 1 |
| Capacitor | 10µF, 0805 | 3 |
| LED | 5mm, Red (Motor Active Indicator) | 1 |
| LED | 5mm, Blue (Bluetooth Indicator) | 1 |
| Pin Header Connector | 2-pin | 6 |
| Pin Header Connector | 3-pin | 3 |
| Pin Header Connector | 4-pin | 1 |
Benchmark: Existing Solutions & Inspiration
System Integration
System Integration is the process of connecting different subsystems or technological components into a single, cohesive architecture that functions as a unified system. Its main goal is to ensure that independent elements—whether hardware, software, or both—work together in a coordinated manner to perform complex tasks that they could not achieve individually. This process involves establishing communication between various modules, ensuring interface compatibility, and designing a centralized or distributed control logic that enables efficient system operation. Integration can include everything from the physical connection of devices to the programming of communication protocols and data synchronization System integration is essential to ensure that sensors, actuators, processors, and user platforms interact properly, meeting the functional, performance, and safety objectives of the system.
You can see the full documentation of the System ingtegration here.
Final Project Design
For my final project, as I mentioned earlier, I am building a motor-controlled exoskeleton for rehabilitation. During this part of the design process, I had many ideas and looked for a lot of inspiration. I also encountered many uncertainties that I wasn’t sure how to solve, but in order to make progress and avoid getting stuck in a loop of ideas, I decided to start by designing the mechanical part first, and then move on to everything else. And that’s exactly what I did.
My design inspiration came mainly from the GrippLyfe glove, a robotic rehabilitation glove designed to assist hand movement, especially in patients with paralysis or muscle weakness. It works through soft pneumatic actuators that inflate with compressed air to flex the fingers in a controlled way. These actuators are connected to an air pump and solenoid valves that regulate the flow to each finger, controlled by a microcontroller. The system allows for smooth and safe movements, mimicking natural muscle function, and can be used in mirror mode to replicate the healthy hand's movements in the affected hand as part of active rehabilitation therapy.
My design idea is to replicate that movement, but instead of using pneumatic actuators, I will use servomotors. These will be placed inside the arm, along with a wristband that attaches to the forearm. This is where I will place the board I designed in Week 8. I will discuss the board and its function later. The motors and the necessary buttons will also be there.
To begin the project, I designed the fingers. Since it is an exoskeleton, it needs to be comfortable and lightweight. I based the design on an artificial tendon system, similar to those in rehabilitation gloves. It mimics the natural biomechanics of the human hand, where forearm muscles pull tendons to move the fingers. In an artificial system, strong threads (like fishing line, Bowden cable, or nylon cords) are attached to the phalanges and routed through guides (such as 3D-printed rings) along the back of the fingers, replicating real tendon paths.
The end of the thread connects to an actuator (usually a servo or DC motor with a spool), which tightens the thread and flexes the finger when it turns, simulating muscle contraction. To return the finger to its original position, passive extension is used, such as elastic bands, springs, or gravity. This system allows for precise movements with low weight, low energy consumption, and high flexibility, making it common in wearable exoskeletons and robotic gloves. Moreover, since it is external, it does not require surgery or invasive interaction with actual muscles, making it ideal for medical rehabilitation or assistive applications.
Using this system, I decided to design a ring-type support in SolidWorks. It doesn't fully close, as it will be adjusted with Velcro straps to ensure user comfort. A closed ring design posed problems due to finger swelling throughout the day from factors like fluid or salt retention. An adjustable system can adapt to these changes, preventing discomfort or misfit.
I started with some sketches of how the rings might look. These are the initial sketches:
Then I created the design in SolidWorks. My first design was a test to determine the right measurements. I also printed it in 3D using the Prusa MK40 with PLA material to better visualize the dimensions. Here's the design, print parameters, and how it looks:
I later redesigned it, as the first one was too big. After remeasuring and redesigning, I printed the new version with the same settings. This time, it was too small, but it turned out perfect for the pinky finger.
Next, I modified the design to make it slightly taller for the medial phalanges of the index, middle, and ring fingers, allowing Velcro to be inserted from below. Only the height of the Velcro slot was changed. I printed it again, and it fit perfectly.
For the proximal part of the fingers (which are slightly wider), I adjusted the arc of the design to make it broader. I printed it, and it fit well on the middle, ring, and pinky fingers.
Note about the Thumb: For the thumb, I found that two of the proximal rings fit perfectly. I only needed to print two of those pieces.
Afterward, I printed all the fastening parts for the fingers and added Velcro. Here’s how they looked and the print parameters used for the remaining pieces:
Electronic Board Design
As part of Week 6 of the Fab Academy, I designed a custom PCB specifically for my final project. The board is compact and allows control of three servomotors for the fingers of the assistive device. It also supports voice or button inputs and provides stable power handling for wearable use.
Design Highlights
- Microcontroller: Xiao Esp32C3 chosen for its small footprint and sufficient I/O.
- Servo Control: five PWM outputs dedicated to the little, ring, index, middle, and thumb fingers.
- Power Management: Includes voltage regulation to separate logic and servo power.
- Programming Access: UPDI and debugging pads for easy programming and testing.
You can find the full design files, schematic, and milling process on my documentation page for Week 06 - Electronics Design.
Next Steps
- Refine the design using 3D modeling
- Prototype different control mechanisms
- Test different actuators and materials