**4.9 Component and materials selection**

The wheelchair frame is made up of Aluminium because of its strength, light weight, corrosion resistance and resistance to shock loads that will be imposed on it during operation. Also the arm rests are also made of Aluminium as well as the spiral lift telescoping arm assembly. The leg rests are made of iron which is chosen for its high tensile strength as it will bear the body weight of the user when standing up. The seat, back and head rest are made up of silicone and are covered in foam cushion to enhance comfort to the user. While the wheels are made of rubber because of its excellent ability to absorb shock.

The joystick module which controls the power of wheelchair consists of command buttons and a knob. The module has 8 button commands namely:


The joystick module is connected to the wheelchair's microcontroller/power module and these two communicate with each other using serial communication protocols. The speed and steering commands that are input by the user are converted to data packets by the internal processor of the joystick and then sent to the microcontroller via serial communication.

Finally the microcontroller module is the main system of whole wheelchair and it receives all commands from the joystick module and translates the commands into high current signals to the motors and mechanism actuators, receiving power from the 24 V battery power. Despite its small size, the power module is able to deliver a very high current per electrical motor and actuator.

#### **4.10 Economic analysis**

An effort was made to compile the cost and quantities of raw materials, and components as well as the cost of manufacturing a prototype. The grand total cost was about USD 1 511.


**Table 4.** *Bill of quantities (BOQ ).*

From the costing analysis and evaluation carried out above, the wheelchair design proved to be relatively affordable compared to other wheelchairs on the market that can operate similarly.

### **4.11 Design validation summary**

The evaluation of the design against the customer requirements as summarised by the **Table 4** below.

The design is fully automated with the drive, lift and recline mechanisms being controlled autonomously. It assists the user in elevating and reclining easily with use of sensors and intelligent awareness that prevents accidents and collisions. The design mechanism takes about 10 seconds in elevating to max height which makes it safe and efficient in handling the user with delicacy. The wheelchair allows the user to move around easily as well as perform more activities independently with the assistance of the wheelchair intelligence system. The design also includes a charging port to charge the battery (**Table 5**).
