# Smart Electric Three-Wheeled Unit for the Manufacturing Industry
## 2 Materials and Methods
### Transmission Gear  
The advantage of using a chain-driven propulsion system for the electric smart tricycle, as opposed to a direct drive from the motor to the rear wheels, lies in the flexibility it provides in adjusting the gear ratios. The gear ratio between the front and rear gears directly influences the tricycle's top speed and its torque or pulling force. With the motor equipped with a 46-tooth sprocket, the choice of rear sprocket size in the derailleur dictates the gear ratio, and thus, the overall speed capabilities of the tricycle. Selecting the rear sprocket's size is critical and is typically based on standardized components common in electric bicycles. This size determination involves calculations that factor in the motor's rotational speed per minute (RPM), as specified in the manufacturer's technical sheet, and the diameter of the rear wheels. The technical sheet for the Bafang BBS-02 motor (Table 1), for example, lists a maximum rotation of 135 RPM (nT = 135 min\({}^{-1}\)), which equates to 2.25 motor rotations per second, correlating to the sprocket's rotations. This detailed approach to gearing allows for nuanced control over the tricycle's mechanical output, optimizing it for various operational needs whether it be achieving higher speeds or increasing torque for better pulling power. \[nm=2.25\;\mathrm{s}^{-1} \tag{1}\]  
The rear wheel has a diameter of 10 inches, which means that one rotation of the wheel while the tricycle is moving will equal a travelled distance of 0.79 m.  
\[O_{bol}=0.79\;\mathrm{m}; \tag{2}\] \begin{table}
\begin{tabular}{c c} \hline \hline
**Position** & **Mid Motor** \\ \hline Construction & Gear Drive \\ Rated Voltage (DCV) & 48 \\ n0 (Rpm) & 160 \\ Rated Power (W) & 750 \\ nT (RPM) & 135 \\ Max Torque & 160 N.m \\ Efficiency (\%) & \(\geq\)80\% \\ Pedal Sensor & Speed \\ Shaft Standard & JIS \\ Noise Grade (dB) & 55 \\ Operating Temperature & \(-20+45\;^{\circ}\mathrm{C}\) \\ Reduction Ratio & 1:21.9 \\ IP & IP 65 \\ Certifications & CE/EN 14764/ROHS \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technical sheet of Bafang motor. Figure 7: Control unit and Bafang 750 W BBS-02 motor (Suzhou Bafang Electric Motor Science—Technology Co, Ltd, Suzhou, China). In the parameters for the design of the three-wheeled unit, a maximum speed of 12 to 15 km/h was determined. We used the average for the design, i.e., 13.5 km/h, as follows:  
\[\mathrm{V_{max}}=3.75\;\mathrm{ms^{-1}} \tag{3}\]  
The required number of revolutions of the rear wheel for the maximum speed was, therefore, calculated from the maximum speed and the circumference of the wheel. \[n_{kol}=\frac{v_{max}}{o_{kol_{1}}}=\frac{3.75}{0.79}=4.68\;\mathrm{s^{-1}} \tag{4}\]  
In this case, the required gear ratio between the electric motor and the rear wheel is:  
\[i=\frac{n_{kol}}{n_{m}}=\frac{4.68}{2.25}=2.08 \tag{5}\]  
The number of teeth required for the rear derailleur sprocket was calculated from the relationship:  
\[i=\frac{Z_{m}}{Z_{kol}}=\frac{n_{kol}}{n_{m}}=2.08\;=>\;Z_{kol}=\frac{Z_{m}}{i}= \frac{46}{2.08}=22.11 \tag{6}\]  
Given that standardized gearings have options for the number of teeth, such as 18, 20, 22, 24, or 26, the closest number to the calculation which was selected was a 22-tooth derailleur sprocket (Figure 8). To enhance the clarity of our analysis and ensure a comprehensive understanding of the calculations presented in this study, we provide detailed definitions of the variables used in the formula for calculating the required number of revolutions of the rear wheel:  
* \(\mathrm{n_{kol}}\)  
This is the required number of revolutions per second of the rear wheel to achieve the desired vehicle speed. This variable is directly influenced by the operational speed of the motor and the gear ratio. * \(\mathrm{V_{max}}\)  
This is the target maximum speed of the three-wheeled unit, which sets the operational goal for the vehicle's performance in terms of speed.