Introduction: Exoskeleton for a Weak Leg - the Automatic Walking Aid

About: I am currently a high school senior (12th grader) in 'The International School Bangalore'. I am a maker and an innovator at heart, a tech enthusiast, and a varsity soccer player.

[I would like to enter this instructable in Arduino Contest in the junior category]

At the age of 60-65, millions of people have damaged knees, restricting their ability to walk, including my beloved grandfather, who met with an unfortunate accident and currently has trouble walking! There are some devices to solve these problems, but they are usually too expensive and/or not effective. To solve this problem for my grandfather and others suffering from this, I thought of making 'The Automatic Walking Aid' which is affordable and effective for everyone to address knee and leg problems.

This device goes around the thigh, consisting of a flex sensor, an Arduino Uno, a motor driver, and a motor. The flex sensor will detect if the person intends to move his or her leg, inputting the data to the Arduino Uno which commands the motor driver to turn the motor clockwise, counter clockwise, or not at all.

With that introduction and background information, let's get started!

Attached here is the overview video of my project/instructable.

Step 1: Components and Their Details

Device and the Material:

1a. Flex sensor

The flex sensor is the component which starts the whole cycle. It detects whether the person wants to bend or straighten his or her knee or not in a vector quantity, meaning it detects whether the person wants to move his knee front or back. Unlike the other electronics, the flex sensor is mounted on the flex sensor structure, near the knee, to detects its change in position.

1b. Belt (old)
A small length of any used waist belt to support the flex sensor at the knee and to attach the velcro to.

2. Arduino Uno

The Arduino Uno is the brain of the device. It takes the readings from the flex sensor and converts it into a signal the motor driver can read. This signal commands the motor driver do one of these three things: turn the motor clockwise, counterclockwise, or off. The Arduino is mounted onto the thigh strap and is connected to all of the other electronics.

3. Motor

(The above drill motor works for a person 75 kg or lesser. For detailed calculations on why this motor or how I arrived at this, please see the next step)

The motor, a 3Nm, 200rpm, Black and Decker drill motor, is the component which actually lifts the leg to aid and match the person's stride. It receives the power from the motor driver and lifts the leg up or down, based on the polarity the power is supplied by the motor driver(H bridge). The motor is also mounted onto the thigh strap and connected to the motor driver.

4. Motor driver(L298N)

The L298N motor driver connects the motor and Arduino. It detects the signal from the Arduino and powers the motor up to 12V in a specific direction or not at all. Like the Arduino, the motor driver is mounted onto the thigh strap and connected to its respective components there.

5. LiPo Battery

The battery I used has enough energy to power the whole device and last for approximately two hours. It also charges quickly. The battery is a 7.4V 1500mAh 20c lipo battery. Like most of the electronics, the battery was mounted onto the thigh strap and connected to the motor driver, with a switch in the middle to turn the device on and off.

Material for leg lifting mechanism

It consists of pulley, cable, and sandal. The pulley is turned by the motor causing it to wind the cable. Because the cable is connected to the sandal which the person has placed his foot in, the sandal lifts the leg up.

6. Pulley

Below are couple of links for pulley, use the one that's right for your motor and your needs. For this project, finally I had to use a bottle cap that's wide enough to support the pulley-belt and preventing it falling of the rim. It was challenging.


b. 2.5mm radius, 2mm thick -

7. Pulley-belt

This is a thin rubber-like material to go around the pulley to help lift the leg. This can be cut from the bike/cycle tube for the desired length.

8. Sandal

Sandal of the person who will be using this walking aid

Structural and Supporting Material

9. Frame:

A light metal/steel sheet of dimensions -- 1-2mm x 300mm x 150mm

This frame should be curved and fit nicely around the thigh. It consists of two primary components, the thigh strap and the flex sensor structure as shown in the diagram. All the electronics along with the motor and battery are mounted on the thigh strap along with the cushion for the person. There are also screws which allows the person to adjust the length of the flex sensor structure.

10. Velcro Strap

150mm x 100mm (Titanium/grey color) -

Tools and Safety Materials:

11. Laptop to program - to write, compile and run the program using Arduino IDE

12. Cable(printer cable) - to upload the program to Arduino

Printer cable or the cable that comes with Arduino Uno

13. Soldering Iron - to connect and make the circuits with electronic components

14. Wires - to make the connections between various electronic components

15. Goggles - to protect eyes while soldering

16. Gloves - to protect hands while soldering

17. Socks - to cover the frame that goes around the thigh

Step 2: Calculations for Motor Specifications(optional Step, Can Skip It)

This step shows the detailed calculations to figure out the motor specifications needed for an average adult(see the attached pics). I have based my calculations on my grandpa’s leg. This step can be skipped and it is provided here only for someone if interested to know the details. Link to the (drill)motor that is used is given in the previous step(Components and their Details).

Step 3: Make the Circuit

Please see the circuit diagram and the video in this step for the connections made between the electronics(flex sensor, arduino, motor driver, motor and the battery).

The Arduino is the brain of the device and is connected to the motor driver because it needs to signal the motor driver how to power the motor based on its input from the flex sensor (make it spin clockwise, counterclockwise, or not at all). The Arduino is connected to the flex sensor, so the flex sensor can feed its data to the Arduino. The battery is connected to the motor driver and the Arduino. This is because the motor driver powers the motor and the Arduino. Finally, the motor driver is connected to the motor because it powers and controls it.

Please refer to the below link to understand further in detail

Step 4: Program and Test It

Before mounting all the components on the frame, write the software code to detect any changes in the flex sensor's resistance as it bends in certain direction and output the instructions for the motor to rotate in that particular direction(clockwise or anti-clockwise). Sample code(Knee_Movement_Program.ino) is attached here in this step.

Test the program by bending the flex sensor in either directions to see motor rotating accordingly as shown in the attached video. Also, in the program, adjust the motor speed to the right walking pace that is comfortable to the user.

Step 5: Mount the Components Onto the Frame

Once the program is ready, and preliminary testing is done, mount all the components onto the mounting brace that goes around the thigh. Please refer to the pictures and the description below.

1. Cover the frame with a nice cover made of thick cloth, or a thick sock which is easier to just slide it over.

2. Mount the Arduino, motor driver, motor and the battery after soldering the connections between them in a compact, snug way.

3. Make sure the motor is in the back of the thigh and not obstructing to other thigh.

4. The flex sensor and the velcro are attached to the belt strip which is attached to the frame. Make sure the flex sensor part of the belt sits right behind the knee with the help of velcro as shown. When the knee is bent or stretched, the flex sensor also bends and arduino detects the bend and the direction of bend, as the flex sensor's resistance changes.

5. Now, attach the pulley to the motor and secure the pulley-belt onto the pulley at one end and sandal on the other end. Note: Getting the pulley fit to the motor shaft correctly and pulley-belt not to fall over the rim is somewhat challenging.

6. When the mounting and fixing is done, turn on the switch to make the connection, bend the flex sensor in both directions and see the motor turning in the right direction each time.

7. Before putting it on, you can do a load test by attaching 1 kg to the pulley-belt and see if the motor is capable of lifting it as shown in the picture.

Step 6: Finally, Wear It and See It Helps You Lift the Leg

Let the person with weak/disabled leg wear the brace around the thigh with velcro and slip on the sandal. Bend the knee and try to lift the leg a bit to walk, watch the device/walking aid help him/her to walk with very little effort. The motor changes its direction as the leg bends and moves back and forth.

This device is affordable and costs < $100!

Happy Making!