WeArm Prosthetic

WeArm is an open source low-cost, low-complexity prosthetic device with human-like range of motion and touch feedback.

Disclaimer

Information contained in this documentation is limited to material and building instructions needed to start testing.

Testing the WeArm has not been completed due to a problem in I2C communication and needs more work and inputs. The I2C communication between I2C Master (Hand Teensy 4.0) and I2C Slaves (PCA9685, TCA9534, MPL115A, Socket Teensy 4.0) has shown instability.

Attribution

This project is built on the work of Okezue Bell, the creator of WeArm prosthetic. All information including contact details, license terms, original build manual, and other work can be found in WeArm Open Source Build Manual

This page is descripting building a right-hand prosthetic. If you are interested to build a left-hand device, please refer to the original work in WeArm Open Source Build Manual.

Downloadable files are provided by, or built on the files provided by Okezue Bell in WeArm Open-Source Build | Code, Diagram, & Print Files

Things to buy

Material List

Table below is sorted by supplier. In some places, most of listed material could be found in local market. In addition to the list below, you will need 12 VDC power supply, 7.4 V battery with charger if you plan to use batteries, workshop tools like Dremel and soldering station.

Printed Circuit Boards (PCBs)

There are 3 PCBs in the WeArm project. To order a PCB (unpopulated), you will need the associated Gerber file for each board, which can be generated using the Eagle software. All Gerber files are uploaded and ready for use. To learn about generating Gerber files in Eagle, refer to this link.

Item	Type	Pcs.	Eagle File	Gerber File	Image
Main microcontroller palm PCB	4-layer	1	File:MC-Eagle.zip	File:MC 2023-08-07.zip
EMG socket PCB	2-layer	1	File:EMG-Eagle.zip	File:EMG 2023-07-16.zip
Pressure sensor PCB	2-layer	6	File:Haptic-Eagle.zip	File:Haptic-F 2023-07-16.zip

Preparations

STL 3D Printing Files

Part	Quantity	Material	STL	Image
Back palm	1	PLA+	b-palm
Front palm	1	PLA+	f-palm
Back palm mold	1	PLA+	b-palm-mold
Front palm mold	1	PLA+	f-palm-mold
Thumb holder	1	PLA+	thumb-holder
Thumb unit	1	PLA+	thumb-single-unit
Thumb skin	1	PLA+	thumb-skin
Thumb skin mold right	1	PLA+	mold-thumb-skin-r
Thumb skin mold left	1	PLA+	mold-thumb-skin-l
Finger proximal unit	4	PLA+	r-proximal
Finger distal unit	4	PLA+	sm-distal
Distal unit skin	1	PLA+	sm-distal-skin
Finger mold right	1	PLA+	mold-distal-r
Finger mold left	1	PLA+	mold-distal-l
Wrist holder front	1	PLA+	p-f-wrist-s
Wrist holder back	1	PLA+	p-b-wrist-s
Wrist damper	1	TPU	damper
Link	4	PLA+	link
Sleeve	8	TPU	sm-ring-sleeve
Bearing	6	TPU	sm-bearing

Steel Rods

Rods of different diameters (2mm, 3mm, 4mm) are used to connect WeArm components and ensure relative movement between them. Use Dremel tool to cut the rods to size, grind the D-shaped axis, and grind cut edges as well.

Diameter	Cut length	Quantity	Where used	Image
2 mm	9 mm	4	Link with back palm
2 mm	11 mm	4	Link with finger distal unit
2 mm	14.5 mm	4	Finger distal unit with finger proximal unit
2 mm	22 mm	2	Hold distal unit in place when silicone molding
3 mm	9.3 mm	1	Worm gear shafts - thumb motor adduction/abduction
3 mm	9.3 mm	1	Worm gear shafts - thumb motor flexion/extension
3 mm	14 mm	4	Worm gear shafts - finger motors
4 mm	19.5 mm	4	Wheel gear axes - fingers
4 mm	18.8 mm	1	Wheel gear D-shaped axis - thumb adduction/abduction
4 mm	34 mm	1	Wheel gear axis - thumb flexion/extension

Worm Gear/Wheel Gear

1

Grind worm gears (6 pcs.) to a flat surface at one end, and then drill a through-hole using 2.5 mm drilling bit. Create a thread using M3 x 0.5 mm tapping bit, and use the M3 x 0.5 mm socket set screws supplied with the gear set

2

Cut the hub of wheel gears (5 pcs.) using the Dremel tool. One wheel gear will be used uncut as supplied.

Palms Silicone Molding

ECOFLEX 00-35 is used to create the soft coating for back and front palm. Before working with ECOFLEX 00-35 silicone, make sure to read the instruction and take care of pot life and curing time.

Fingers Silicone Coating

Dragon Skin 00-20 is used to create silicone coating for all fingers (little, ring, middle, index, and thumb). The steps to make the silicone coating for little and ring fingers and the steps to make the silicone coating for middle, index, and thumb fingers are not the same. Middle, index and thumb fingers have touch sensors below the silicone coating (2 sensors for each finger). Before working with Dragon Skin 00-20 silicone, make sure to read the instruction and take care of pot life and curing time.

Little & Ring

1

3D printed parts needed: finger distal unit, finger mold right, finger mold left

2

2 rods 2 mm x 22 mm used to hold rigid part in place inside the mold

3

The inclined surface is used as a cutting guide to remove excess silicone

4

Little and ring fingers after molding and removing excess silicone

Middle & Index

Using distal unit skin, finger mold (right and left), and 2 rods 2 mm x 22 mm, follow the same steps used in little and ring fingers molding. The result will be a hollow silicone skin that will be used to cover the distal unit with sensors for each finger (middle and index)

Thumb

Using thumb skin unit, and thumb skin mold (right and left), and any 4 mm rod, follow the same steps used in little and ring fingers molding. The result will be a hollow silicone skin that will be used to cover the thumb unit with sensors

Assemblies

Electronics and PCB Soldring

For completing the PCBs, you will a work station including an iron gun and heat gun. Always use solder paste for SMD components.

Teensy 4.0

In this project, the Teensy will be supplied using an external power supply (12 VDC or 7.4 VDC batteries). By default, the V_in in Teensy board is connected to V_USB by a small bridge in the back side. This bridge should be cut before connection to an external power supply.

Power Supplies

Supply 12VDC (or 7.4VDC battery) to the 5VDC and 3.3VDC step-down convertors. Note the power supply, convertors, and PCBs have a shared ground.

Main MicroController Board (MC)

All touch sensors, motor encoders, and I2C communication wires to the EMG baord should be soldered or connected to the MC board. The board is powered using 5VDC, 3.3VDC, and GND.

After adding a new component that is a part of the I2C network (PCA9685, TCA9534, MPL115A, EMG socket PCB), upload the I2C scanner from Wire library and run the scan to make sure that the recently added part is detected correctly. Refer to Software section for the libraries to be used.

EMG (Socket) Board

The board is powered using 5VDC and GND. Note that when using the step-down convertors, the LM7805 voltage regulator is not needed.

For I2C, connect SLA (Teensy: pin18) and SCL (Teensy: pin19) from EMG board to SLA and SCL wirepads in MC board.

For the electrodes, connect ground electrode (elbow) to GNDEL wirepad, and connect 3 electrodes (2 on arm, 1 on biceps) to any 3 positive inputs of ADS1298 in EMG board.

Touch Sensor

For each touch sensor, you will need 5 wires, 10 cm each. Make sure to use small gauge wires (AWG22 or AWG24). After completing soldering the PCB and wiring, it is recommended to test each sensor using Arduino UNO board. Use the built-in example "getpressure" in Adafruit_MPL115A2 library. If everything is OK, you should get reading of temperature and pressure, depending on your location.

Each touch sensor should be wired to the MC board. The table below shows the mapping between touch sensor wires and MC wirepads. This should be repeated for all touch sensors.

Magnetic Encoders

Before starting fingers assembly, solder the magnetic encoders to the micro motors and insert a magnetic disc to the back shaft of each motor. Insert a worm gear into each motor front shaft, and fasten the socket screw.

Each motor encoder should be wired to the MC board. The table below shows the mapping between motor encoders wires and MC wirepads. This should be repeated for all encodres.

Little, Ring, Middle, Index

1

Use suitable glue to fix the wheel gear into the proximal unit, and use 4 mm x 19.5 mm shaft to secure the wheel gear in place while glue is curing

2

Attach the motor into the back palm using the snap-fit, and then insert the 3mm x 14 mm shaft from the front side of back palm into the worm gear. Insert two TPU bearings.

3

Using 4 mm x 19.5 mm shaft, connect the proximal unit into the back palm. Insert two TPU sleeves into the proximal unit

4

Using 2 mm x 11 mm shaft, connect the link with the distal unit

5

Using 2 mm x 14.5 mm shaft, connect the distal unit with the proximal unit, and using 2 mm x 9 mm shaft, connect the link with the back palm

6

For middle and index fingers, two pressure sensors are needed for each

7

Same assembly steps are followed for the middle and index fingers. Make sure to route the wires as shown

8

Use the silicone skins made before to cover the middle and index fingers

Thumb

1

Insert the uncut wheel gear into the thumb holder part

2

Using 4 mm x 34 mm axis, install the thumb holder with gear into the back palm

3

Insert the micro-motor with the encoder. Make sure the encoder connector is on the back side of the thumb

4

Insert a wheel gear (cut) into thumb single unit part, then using the D-shaped 4 mm x 18.8 mm axis, install the thumb single unit part with gear into the thumb holder

5

Another view for the previous step

6

Two pressure sensors are needed for thumb

7

Connect the motor encoder and route the wires as shown

8

Use the silicone skins made before to cover the thumb

Software

Files Download

File:WeArm-Code.zip

File:WeArm-libraries.zip

Arduino Setup

To enable Teensy 4.0 programming, Teensyduino should be installed on Arduino. For more information, refer to Download Teensyduino. Please note tha this project is completed using Arduion IDE version 2.1.1

Also, the Adafruit PWM Servo Driver Library Adafruit_PWMServoDriver.h (and its dependencies) should be installed using the Arduion library manager.

Some of the default libraries in Teensyduino should be replaced with updated ones (Wire.h, SPI.h). To complete this,

1. Open the hand-control code, and in hand-control. tap, pause the mouse over the Wire.h library. Location folder will be displayed.

2. Copy the location folder and open "libraries" folder.

3. Replace both Wire and SPI folders with the ones downloaded from this page.