# Manual Wheelchair Equipped with a Planetary Gear-Research Methodology and Preliminary Results
## 2 Materials and Methods  
### The Description of Developed Design  
The study was carried out on an operator of a wheelchair equipped with multi-speed gears integrated with powered wheels. At the core of the described design is a planetary gear that gives the user the possibility to smoothly change gears. The planetary gear itself (sun gear with external teeth, gears and carriers) is a compact mechanism that can move along the main wheel axle. This provides the ability to change the drive parameters while linking the handrims delivering the rotational torque to the hubs driving the large wheels.  
A view of the assembled system is presented in Figure 1. The view of the diagram of the designed planetary gear is presented in Figure 2. The system works as follows. The torque generated by the operator's limbs is introduced to the system through handrims (10). The handrims (10) are coupled with the internal gear hub (11) to enable the power transmission. The torque ratio changes as a result of switching the operating mode of the planetary gear (mounted into the hub), described later in the study. From the internal gear hub (11), the torque is transmitted via a system of spokes mounted to the hub flange (9) onto tires (8). As a result, the handrims (10) can rotate at a different speed than the tires (8), thus realizing different ratios.  
The transmission is equipped with a splined couplers assembly (Figure 2a), so that the torque from the planetary gear is delivered to the hub by a splined disc (1) and a splined ring (2). The transmission consists of a bearing system (Figure 2b), which determines the positions of the carrier (3) with the planetary gears, the sun gear (4) and the ring gear (7). A set of four bearings: two radial (5) and two axial (6) were used for the positioning all of the moving elements. Radial bearings maintain the axis of rotation of the carrier with the axis of the sun gear. In contrast, the axial bearings reduce the friction between the carrier and the ring gear assembly. In addition, the axial bearings position the ring gear assembly relative to the carrier and the sun gear assembly.  
A kinematic diagram of the solution is shown in Figure 3. The planetary gear works for all gears with the sun gear (14) locked. The gear shift depends on the input and output of the transmission. In the first gear--Figure 3a, which gives a reduction in the rotational speed--the torque from the handrims is transferred to the sun wheel (14) with internal teeth (12) through the planetary gear (13) and is delivered from the carrier (15). In the second, neutral gear--Figure 3b--the torque is delivered to the sun gear (14) through the planetary gear (14) with internal teeth (12) and it is passed on from here. In this case, the carrier (14) also rotates, but it is not picked up by the hub. In the last, third gear of the mechanism--Figure 3c, which is a multiplier of rotational speed--the torque from the handrims is delivered to the planetary gear carrier (15) and is picked up from the sun gear (14) through the planetary gear (13) with internal teeth (12).  
Figure 1: View of the assembled system: 8—tire, 9—system of spokes mounted to the hub flange, 10—handrims and 11—internal gear hub.  
Figure 2: View of the diagram of the constructed planetary gear: (**a**) view of the internal gear hub and methods of coupling the planetary gear; 1—splined disc, 2—splined ring, (**b**) view of the bearing system of the carrier inside the planetary gear; 3—carrier, 4—sun gear, 5—radial bearing, 6—axial bearing and 7—ring gear (internal teeth).  
The internal gear hub prototype was made to a scale of 2:1. This was decided upon because of the assembly and testing processes simplification. For the same reason, the prototype was equipped with only a simplified gear shift mechanism. The device was mounted on a V300 Vermeiren wheelchair. The assembly required the use of a suitable adapter connecting the central axle of the hub with the wheelchair frame. The device was compatible with 24 inch, double-chamber rims and 3 mm diameter spokes.