# Design Considerations Concerning an Innovative Drive System for a Manual Wheelchair
## 2 Materials and Methods
### Design Considerations Based on a 3D Model  
A 3D model of the developed wheelchair's hub design based on the patent application P.434936 (Patent Office of the Republic of Poland, 2023) is shown in Figure 2. A ball bearing (3) and a needle bearing (4) are fitted between the upper (1) and lower (2) housings, which have been secured against displacement by means of a housing flange. The needle bearing (4) is supported by a hollow outer shaft (5), the center of which features a needle roller thrust bearing (6). The second support point of the outer shaft (4) is the sprocket wheel hub (7), which is secured against displacement by a stopper ring (8). The sprocket (7) is seated on the outer race of the ball bearing (9) supported by a stopper ring (10). Inside the outer shaft (5) is a hollow inner shaft (11), which is supported on the inner races of the needle roller bearing (6) and the ball bearing (9). On the gearbox side, the inner shaft (10) is secured with a sliding sleeve (12), bearing nut (13) and bearing washer (14). The outer shaft (5) is fitted with the wheelchair's wheel hub (15), which is secured against displacement by a stopper ring (16). The pushrim hub (17) is fitted onto to the inner shaft (11) by a keyway connection (18), on the needle roller bearing (6) side. The pushrim hub (17) is supported by a lock nut (19) screwed into the thread of the inner shaft (11). The solution is attached to the wheelchair frame by the frame clamp (20) from below and by dedicated holes in the top frame (1) from above. The design discussed differs in terms of the length of the sprocket wheel hub (7) and the inner shaft (11) in the left and right wheels, which is due to the method of connection to the gearbox and torque gauge.  
The next step in the design process was to develop the method of fitting the created drive system to the wheelchair's frame. The Vermeiren V300 wheelchair (Vermeiren Poland, Trzebnica, Poland) was chosen as the basis for this task, thereby enabling the determination of the frame's geometry. The final stage of the system's construction required the modeling of its remaining components. Once the non-standardized parts were designed and standardized components selected, their geometry was mapped in the CAD environment. This enabled the development of an overall assembly of the prototype drive system solution for the left and right wheels.  
It is worth mentioning that the right wheel assembly had to be modified due to the lack of a torque gauge and the bicycle derailleur's inability to work in a mirror image. This is an important issue and a significant technical problem to solve in the future, as such a solution is disadvantageous. The prototype after complete assembly is shown in Figure 3.  
Figure 3: _Cont._  
Figure 2: View of the 3D model of the developed wheelchair hub structure for the drive system on the left side of the wheelchair; (**A**) hub in isometric view, (**B**) half of the hub in isometric view.  
The current prototype version (proof of concept) has a mass of 43 kg, and this would need to be reduced in a commercial system. Such weight results from the installation of the drive system in a ready-made, commercially available wheelchair. Designing the solution from scratch based on an FEA strength analysis carried out for structures made of lightweight alloys or composites would probably reduce its mass [21,22]. As part of optimizing the mechanism, it is also worth paying attention to the development of micro air vehicles, which also utilize modified chain drives as presented in several studies [23,24]. Moreover, minimizing the weight of the wheelchair will directly translate into a reduction in the value of forces acting on the wheelchair-human system, reducing, for example, friction forces [25,26].