# A Stair-Climbing Wheelchair with Novel Spoke Wheels for Smooth Motion
## 5 Experimental Validation  
### Prototype Fabrication  
In terms of prototype fabrication, different manufacturing processes were selected and customized based on the characteristics and functions of each component. The key parts of the spoke wheel mechanism were made of stainless steel and manufactured using CNC machining to ensure structural precision and durability. The seat and motor housings were fabricated through 3D printing, while the baseplate and motor mounting plates were cut from carbon fiber sheets, achieving a lightweight yet high-strength structure. The combination of multiple manufacturing techniques not only enhanced the overall structural stability of the design but also significantly improved the wheelchair's reliability and service life. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Motion Mechanism** & **Stair Specifications** & **RMS of Z-Axis** \\  & & **Acceleration** \\ \hline Traditional spoke wheels & 2 cm \(\times\) 4 cm & 0.48 m/s\({}^{2}\) \\ Flexwheels & 2 cm \(\times\) 4 cm & 0.39 m/s\({}^{2}\) \\ Traditional spoke wheels & 3 cm \(\times\) 10 cm & 0.51 m/s\({}^{2}\) \\ Flexwheels & 3 cm \(\times\) 10 cm & 0.42 m/s\({}^{2}\) \\ Traditional spoke wheels & 4 cm \(\times\) 8 cm & 0.52 m/s\({}^{2}\) \\ Flexwheels & 4 cm \(\times\) 8 cm & 0.47 m/s\({}^{2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of stair-climbing vibration performance between traditional spoke wheels and Flexwheels based on simulation. Figure 12: Simulation results of stair climbing. Based on Equation (22), the rear wheels of the prototype should be equipped with springs of \(k^{\prime}{}_{\text{REAR}}=40.25\text{N/m}\). By maintaining the front-to-rear spring constant ratio from the simulation model, the front-wheel spring constant for the prototype was determined as follows:  
\[k^{\prime}{}_{\text{FRONT}}=\frac{k_{\text{FRONT}}}{k_{\text{REAR}}}.k^{\prime}{ }_{\text{REAR}}=26.42 \tag{24}\]  
where \(k_{\text{FRONT}}\) and \(k_{\text{REAR}}\) represent the spring constants of the front and rear wheels in the simulation model, respectively, and \(k^{\prime}{}_{\text{REAR}}\) is the rear-wheel spring constant for the physical prototype. By testing prototypes with various front-wheel spring constants, the minimum pitch angle variance was achieved when \(k^{\prime}{}_{\text{FRONT}}=26.42\text{N/m}\). Therefore, the final prototype configuration adopted rear springs with \(k^{\prime}{}_{\text{REAR}}=40.25\text{N/m}\) and front springs with \(k^{\prime}{}_{\text{FRONT}}=26.42\text{N/m}\). To enhance the intelligence of the wheelchair, the control system integrates multiple sensors, as illustrated in the block diagram in Figure 13. The controller adopts the high-performance STM32F407 VET6 microcontroller (Manufactured by STMicroelectronics, located in Geneva, Switzerland), which includes an onboard IMU for the attitude sensor. The wheelchair's bus servos support two operational modes: servo mode and geared motor mode. In servo mode, the servo enables precise rotational positioning within a 240\({}^{\circ}\) range, while in geared motor mode, it allows continuous 360\({}^{\circ}\) rotation with controllable direction and speed. The selected servos are Hiwonder LX-224 Bus Servo (Manufactured by Hiwonder Technology Co., Ltd., located in Shenzhen, China), featuring a rated voltage of 7.4, maximum torque of 20 kg-cm, and a rotation speed of 50 r/min at no load. The bus servos are controlled via UART-based asynchronous serial communication. The control parameters include the servo ID, target position, or target speed, depending on the issued command. By configuring different operating modes of the servos, the power system ensures precise Flexwheel control and stable self-balancing operation. The wheelchair is equipped with four laser ranging modules (ATK-MS53L1M), which communicate with the microcontroller via UART in Modbus mode. These sensors enable real-time distance measurement, providing critical data for stair detection.