Modular Hand Assist

Introduction: Modular Hand Assist

I’ve seen people with finger injury, missing fingers, or muscle disability having a hard time grabbing things. This might affect their life a lot. Although there are already dozens of assists devices on the market, the price is hard to afford.
Therefore, I start designing an inexpensive wearable device that can help people grabbing things, using chopsticks, etc.
The modular design makes it easy for users to change the module in order to perform different tasks.
Also, an auto-recognition system was designed for the microprocessor to recognize the module type and automatically perform the corresponding task.

Step 1: CAD Design

The structure was designed by me to 3D print

Some important things about the design

1. The gear on the modules is connected to a servo by a spring to make it able to grip different sizes. The force applies to the grip can be customized by adjusting the servo angle to pull the spring harder.

2. An 8 pin connector was designed for module recognition. The spare pins were left for future extension on other modules to connect sensors or other components.

Step 2: Materials & Tools

  • Electronics :

1. Digispark Attiny85 microcontroller

2. HC-SR04 ultrasonic distance sensor

3. SG90 Servo

4. Li-Po battery

5. Li-Po protection and charging board

6. 8-pin male female connector

  • Tools :

Soldering iron

  • 3D printed parts

Stl files inclued

Step 3: Base

The ultrasonic distance detector
When the ultrasonic module detected an object approaching. It will automatically turn on the servo. It will stop when the object removed. For grabbing things, a release button was designed.

Connector design
The connector consists of a Vcc Gnd and a module recognition pin. The microprocessor detects different module types by reading the voltage on the module recognition pin.

There should be a Li-Po battery inside for practical use. For a prototype, an external power source were used.

Assembly steps :

1. Solder all the things together

2. Insert the ultrasonic distance sensor into the two holes

3. Insert the servo into the servo connector and screw it up

4. Put the attiny microprocessor at the right place

5. Glue the top cover

6. Glue the pin header onto the top cover

7. Glue the right cover

8. Tight a band through the bottom of the base to wear it.

9. Base assembly finished

Step 4: Grabbing Module

The module is designed to grab. The claws can be easily removed to put on chopsticks.

Assembly steps :

1. Insert the gear into the top cover (The one with the hole on the left)

2. Glue the claw holder onto the gears

3. Insert the Servo horn then connect it with a spring to the hole on the gear

4. Connect 5v with the module recognition pin

5. glue the top cover with the frame together

6. Grabbing module assembly finished

Step 5: Code & Circuit

Code :
In the beginning, the microprocessor read the voltage of the module to detect the module type. The grabbing one is 5v and the brushing one is gnd.
After that, the ultrasonic distance sensor is used to detect if there’s an object approaching. If so, it will automatically grab the object. If the user removed the object or press the release button, the object will be released.
The parameters can be set in the define section of the code.

Circuit :
P0 : Servo signal

P1 : Release button

P2 : HC-SR04 trig

P3 : HC-SR04 echo

P4 : module detect

8 pin connector :

Pins : 5v, GND, Module recognition
(5v for the grabbing module)

Code Download

Step 6: Other Modules

I’m also designing some different types of modules for this. If anything were done, it will be updated as soon as possible. Thanks for taking a look at this instructables.

Step 7: Future Plans

  • Making a PCB for an SMD Atmega328 or 32u4 for more pins
  • Replace the ultrasonic distance module with a laser one for more accuracy and smaller base

Assistive Tech Contest

Participated in the
Assistive Tech Contest

Be the First to Share


    • First Time Author Contest

      First Time Author Contest
    • Fruit and Veggies Speed Challenge

      Fruit and Veggies Speed Challenge
    • Summer Fun: Student Design Challenge

      Summer Fun: Student Design Challenge



    Question 1 year ago

    What will the other modules be?


    Answer 1 year ago

    A module that I am recently designing is using a rack and pinion system. It can help people brushing their teeth.