UNIVERSITY AT BUFFALO. Design Phase. Remote Controlled Wheelchair With Collision Avoidance

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1 UNIVERSITY AT BUFFALO Design Phase Remote Controlled Wheelchair With Collision Avoidance Joseph D Amato Husein Rashed Steven Ostertag Rohan Vivek T.S. Rockwell

2 The System A. Hardware I. The Raspberry Pi(vs Arduino) - Better Support Python - Better Development Environment SSH, HDMI Output - Tradeoff Less ideal for real-time system II. User Input - The WiiMote - Bluetooth Interface - Well defined python module available - The Joystick - Inexpensive - USB Interface - Well defined python module available III. Sensor Input Ultrasonic - Used for similar applications in cars (backup sensor) - Cheap - Easy to use IV. Motor Control - Controlled with PWM from the Pi B. System Operation I. User in Chair - Operates chair in same manner as standard electric wheelchair II. Remote User - Has ability to gain control of the wheelchair while disabling onboard control - Remote user maintains control of the wheelchair until released - Uses directional pad on remote for forward/backward/left/right III. Safety - Ultrasonic sensors placed strategically to prevent collisions

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8 Software Implementation Major Modules main.py This is the file which is run first when the raspberry pi boots up. It first waits for the wii remote to be connected by pressing button 1 and 2 of the remote at the same time. Once the connection is successfully established, it allows us to choose if we want to control the wheelchair using the remote or the on-board joystick. The input is then decoded and the motors run according to what input is selected. Before the motors are actually powered up the ultra-sonic sensors are used to make sure there are no obstacles in that direction. joystick.py This module is responsible for decoding the inputs from the remote. 1. check_joystick(): It checks the input from the on-board joystick,decodes it and returns the desired direction. It returns the speed that should be passed to the motor controller. wii.py This module is responsible for connecting the raspberry pi to the wii remote and decoding the inputs from the remote. 1. connect_wii(): It is used to connect the wii remote to the raspberry pi. 2. check_remote() : It checks the input from the wii remote decodes it and returns the number of the button that was pressed. Return Values 1- Button 1 2- Button 2 3- Forwards 4- Backwards 5-Left 6-Right 7-Home usonic.py This module is responsible for calculating the distance to objects. 1. reading(sensor) : It takes the pin to which the sensor is connected as an input and returns the distance to the object in front of it.

9 motor.py This module is responsible for controlling the rotation of the motors. 1. forward(speed): It accepts the value speed as an input and rotates both the motors forward at the specified speed. 2. reverse(speed): It accepts the value speed as an input and rotates both the motors backwards at the specified speed. 3. left(speed): It accepts the value speed as an input and switches off the right motor while rotating the left motor at the specified speed to turn the wheelchair left. 4. right(speed): It accepts the value speed as an input and switches off the left motor while rotating the right motor at the specified speed to turn the wheelchair right. Connections (GPIO #s) 1. Sensor_front = Trig: 4 Echo: Sensor_back = Trig: 8 Echo: 7 3. Sensor_left = Trig: 2 Echo: 3 4. Sensor_right = Trig: 17 Echo: Motor_right (1) = PWMH: 25 DIR: Motor_left (2) = PWMH: 23 DIR: Joystick = Usb Future Plans: 1. Use the buttons on the joystick for additional features 2. Power the pi from the wheelchair s batteries 3. Incorporate a backup horn 4. Use an Arduino instead of a pi Reported Problems: 1. The ultrasonic sensors and motor controllers should use ~5V logic, but the pi only delievers 3.3V. We did purchase steppers for this, but we could not figure them out. Through testing the pi s 3.3V GPIO pins seemed to be stable enough to control all modules. 2. The ultrasonic sensor s echo pin returns 5V to an input GPIO pin of the raspberry pi. The pi s GPIO pins are not 5V tolerable; therefore a resistor is needed to prevent damage to the raspberry pi. 3. We went through multiple SD cards due to corruption. A possible culprit is a poor power supply, but it has not been tested. We do recommend making occasional backup images using Win32DiskImager.

10 4. We could not connect the raspberry pi to the internet using a wifi dongle therefore we needed to share internet through a laptop and broadcast it using a router. A static IP address was assigned to the Pi. Steps can be found online. 5. Additional motors controllers were purchased because the other 24V motor controllers were a maximum of 24V. When charging or when the motors come to rest a voltage spike can lead to a high voltage to the motor controllers. 6. We were given a converter for DVI to HDMI to connect a monitor. The pi does not like the converter therefore you will need to force HDMI in /boot/config.txt