By the use of anthropometry parameters from the works of Ajibola et al [23], quality, cost, availability of local materials and their mechanical properties were considered for the design. The basic materials used included mild steel, aluminium, galvanized pipe for the frame work, backrest, seat, leg rest, foot rest, headrest, DC battery, solar module, panel for control buttons, DC motors and other basic electrical components. The 3D modelling and assembling was carried out using CREO parametric version 6.0 application software in order to have accurate dimension and visual illustration of the proposed model as shown in Fig. 1(a, b, c and d comprising of side, front, top and general view respectively) while Fig. 2 represents the exploded view. The prototype of the wheelchair was then fabricated and assembled using locally available materials.
2.1 Design considerations/methods
A 0.5-inch galvanized steel pipe was used for the frame which form the skeleton of the wheelchair, it was cut into different lengths and arc welded, with a half inch sheet of mild steel for covering the base and half-length of angle bar for housing both the solar panel and batteries, while 1 ft sq. fibre for padding the button control. The design specification of polycrystalline solar panel with length, width and depth of 36.6 inch, 12.4 inch and 0,8 inch respectively having a wattage of 50 W, amperage of 2.8–2.95 A and voltage of 17.8 V was chosen. Other factors that were considered in the design was load, and speed. Table 1 shows some other technical specifications of the wheelchair. The maximum speed of the wheel chair was 8.33 km/h (Chien 2014), weight on each wheel, torque, power, energy of the battery and time of its charging were calculated as shown below:
Table 1
Technical specifications of the wheelchair
Taking the maximum speed of the wheelchair as 8.33 km/h, and using the relationship between linear and angular speed, the speed of the wheel required to achieve a desired speed is given as:
Taking max speed of wheelchair as = 8.33 km/h
RPM of shaft wheel (let say N) = (8.33x 1000)/ (60 x 60) = (3.14 * 0.669 * N)/6
RPM = 66
Where d is 0.669 m, the diameter of the rear wheel of the wheelchair, n is the speed of the rear wheel of the wheelchair (rpm).
Weight (on each wheel) = 20 x 9.81 = 196.2 N;
where 20 is an assumed weight on a wheel
Torque (T) = 196.2 x 0.19 = 37.28 Nm; where 0.19m is the radius of the rear wheel
Power = (2 x 3.14NT)/60 = (2 x 3.14 x 66 x 37.28)/60 = 258 W
Energy of Battery = 216 W/hr
Time of Charging = 216/258 = 0.8 hrs
2.2 Connection Procedure
The control system for the wheelchair was designed on a computer using fritzing software so as to validate connections. The control components and modules were then assembled according to the appropriate method of connection represented on the computer design. An Arduino sketch was written in Arduino programming language that was meant to control the module in a required manner. Figure 3 shows the circuit connection for the control panel. However, the voice command was programmed and synchronized with the voice recognition device and then a Bluetooth connection was used to pair the connections.
2.3 Description of the voice controlled and solar assisted wheelchair.
The wheelchair consists of the battery housing, wheels, driving motors, 12 v batteries, solar panel, etc. The front and rear wheels carry the entire components of the wheelchair with the rear wheels fastened to the driving motor. The battery housing carries the fabricated frame upon which the rechargeable 12v batteries sits. The batteries supply electrical energy to the motors, electrical and automation components.
2.4 Principle of Operation
The principle of operating the wheelchair was achieved by the conversion of energy by different components that had been used in the course of its fabrication. The electrical energy of the battery was converted to mechanical energy through the two D.C. motors to the rear wheels for driving the wheelchair. The electric circuit ensures power transfer from the battery to run the D.C. motor, whilst the solar panel powers the wheelchair when in use and help store energy to the battery hence compensating for its discharge. The voice interface was programmed, designed and 3D printed to be held handy by the user while in operation or by a third party to help the disabled. The voice module device had the power button incorporated in it and thus the user receives a welcome message when powered on. The voice module automatically pairs with the wheelchair and recognizes the following commands; forward, backward, left, right and stop. When the user issues a recognized command, the voice module picks the command and transmits to the wheelchair which it is paired to and hence the wheelchair obeys the commands in splits of seconds. However, when the user issues an unrecognized command, the wheelchair sends feedback to the user by making a different beep sound from the recognized command beep. The wheelchair was programmed to accept English and four (4) other local languages. This means, the user will train the voice module on the particular language (using the manual) he/she will want to be using so as to make them recognized commands. The various languages incorporated include the three major languages in Nigeria; Hausa, Igbo and Yoruba or any language of the user’s choice. The system also responded perfectly to the buttons control which was designed as well. A flow chart of the control is as shown in Fig. 4.
The user issues a command using the Sparkfun PID 15453 voice module which is paired to the Arduino Uno R3 board carrying the Atmega328 microcontroller via the ESP8266 HC05 Bluetooth module, it is received as bits by the voice module from the user and then transmitted to Arduino Uno R3; it uses C + + programming language and has its own Integrated Development Environment where the codes were written hence its converts the transmitted audio to signals and sends it to the 12V – 10A electric DC motors passing through the 5 v relay modules where it is interpreted and acted upon to obey the command issued. The DC motors converts the electrical energy supplied from the battery to mechanical energy thereby providing motion which makes the wheelchair move. The 50 W polycrystalline solar panel was connected to a 12 V PWM charge controller which regulates the voltage entering the 12-v battery so as to avoid overcharging or discharging. However, same applies to the system when the user issues a command using the control button. The control buttons were built using resistors of varying capacities which include (10, 8.2, 6.8, 4.7, 3.3, and 33) k Ω. Veroboard was used to connect the various components together. The block diagram for the control algorithm is shown in Fig. 5 below.