6 Finger Augmentation with PocketBeagle

Story :

In this project, I’ve modified existing 3D-printed prosthetic hand to develop a 6th finger prosthetic augmentation in a form of a thumb that attaches to the side of the hand. This project was made with a focus on allowing for a variable grip to reduce the difficulty in grabbing larger objects or holding multiple smaller objects. The STLs for this project was generated through the modification of the existing e-NABLE Phoenix hand design.

This project uses the variable resistance allowed by potentiometer for increased control of the finger movement and can easily be replaced with strain gauges or electronic components that allows for variable resistance. Further development in ergonomic considerations is needed in the forms of changing print design to allow for TPA material to improve fit, optimizing servo location/ wiring to increase usability, and modifying phalanx/fingertip length and surface to improve grip.

Assembly of Hand and Servo :

From the build process of the base e-NABLE Phoenix hand, only the thumb needs to be assembled.

1) Identification of Parts

1. Orthodontic Elastic Rubber Band (3/16’’)

2. Fishing Line

3. thumb_knuckle_pin.stl

4. finger_phalanx.stl

5. thumbtip_pin.stl

6. fingertip_short_v2.stl

7. 6 Finger_v2.stl

8. Velcro Straps (12’’ x 1/2’’)

9. SG90 Servo

stl files for 3, 4, 5, 6 can be found on the following link (e-NABLE Phoenix Hand v2)

2) Assembling the Fingers

a. Gather the following pieces:

4. finger_phalanx.stl

5. thumbtip_pin.stl

6. fingertip_short_v2.stl

b. Assemble the thumb by aligning the rectangular holes in pieces 4. finger_phalanx.stl and 6. fingertip_short_v2.stl

c. Insert piece 5. thumbtip_pin.stlin the rectangular hole and push in completely to generate the 4,5.6 Thumb piece

3) Attaching the Fingers

a. Gather the following pieces:

4,5,6 Thumb piece

3. thumb_knuckle_pin.stl

7. 6 Finger_v2.stl

b. Assemble the thumb by aligning the rectangular holes in pieces 4,5,6. Thumb piece and 7. 6 Finger_v2.stl

c. Insert piece 3. thumb_knuckle_pin.stl in the rectangular hole and push in completely to finish the assembly of the 6 finger augmentation device

4) Applying the Dental Bands

a. Gather the following pieces:

3,4,5,6,7. 6 finger augmentation device

1. Orthodontic Elastic Rubber Band (3/16’’)

b. Attach the rubber bands to both joints outlined in yellow

5) Securing the Servo motor

a. Gather the following pieces:

1,3,4,5,6,7. 6 finger augmentation device

9. SG90 servo

b. Attach the servo from the bottom up on the slot outlined in yellow

c. Secure the servo to the 6 finger augmentation device by screwing in the Phillips screw that comes with the SG90 servo

6) Stringing the Fingers to the Servo Motor

a. Gather the following pieces:

1,3,4,5,6,7,9. 6 finger augmentation device

2. Fishing Line

b. After knotting the fishing line to the end of the servo wing, follow the instruction online for stringing the thumb

7) Inputting the Velcro Strips

a. Insert Velcro strips on the slots outlined in yellow

b. This marks the end of assembly

Operation Instructions :

1. Attachment to Hand

-The Velcro strip further from the servo should wrap around the palm of the hand

-The Velcro strip near the servo should wrap around the wrist of the hand

Operation Video :

2. Adjusting the Potentiometer to Manage Grip

-There is an initial grip of the finger with the device's startup to show if the program is working properly

-Adjusting the resistance with the potentiometer will change the grip level

3. Reading the LCD Screen / LED

- The LCD should update with the potentiometer adjustment to show (ON : "Grip level")

- The Grip level is a 0 - 5 scale with 0 = no grip & 5 = maximum possible grip

- The green LED will light up to signify operation

4. Turning Off the Device

- Press the button to end operation

- The LCD should update to show (OFF)

- The red LED will light up to signify end of operation