9. MECHANICAL DESIGN
9.1 Steps undertaken:
- Study of the typical chair dimensions
- Identification of individual parts and mechanism selection
- Design of components for the expected loads
- 3-D modeling of the components using CATIA
- Fabrication of the components and their assembly
9.2 Specification of motors:
Figure 33: Complete mechanical design of wheelchair.
- Load considered W = 120-150 kg
- Lift desired = 300-350 mm (0.3 m)
Figure 34: Wheel Design
- Material – mild steel
Figure 35: Frame design
9.3 Calculation
- Considering speed of wheelchair v=6 km/hr = 1.67 m/s
- Taking diameter of wheels = 360 mm = 0.36 m
- Angular velocity ω = v/r = 1.67/0.36 = 4.638 rad/s
- Speed n=45 rpm
- Torque T = Fr = (2001.67)*0.18 = 50.1 N-m
- Power P = 2pinT/60 = 2pi4550.1/60 = 236 watt
- P = 236/746.2 HP = 0.31 HP
9.4 Electric motors
- Speed of wheelchair – 6 km/hr (1.67m/s)
- Speed of motor – 100-120 rpm
- Power – 0.25-0.5 HP
- Geared motors
- With internal brakes
9.5 Lifting mechanism
- Hydraulic jack
- Screw jack
- Helical screw actuator
9.6 Screw mechanism
- For reclining movement of backrest and calf-rest
- Lead screw powered by motor
- Rotating links at both backrest and calf-rest
Figure 36: Frame in workshop
Table 4: Component Specification chart
Figure 37: Actuators and motors for lift mechanism
Figure 38: Front Wheel
Figure 39: Screw Jack for lift mechanism
Figure 40: Frame of Wheelchair