# Development of Piezoelectric Inertial Rotary Motor for Free-Space Optical Communication Systems
## 4 Experimental Investigation of Motor
The combined analysis of impedance and phase characteristics (Figure 21) demonstrates that the motor's performance is highly sensitive to temperature changes. At lower temperatures, the motor exhibits higher impedance and remains in a largely reactive state, reflecting reduced mechanical flexibility and increased energy loss due to higher electrical resistance. On the contrary, at higher temperatures, the impedance decreases and the phase shift indicates a stronger real power component, reflecting improved motor efficiency. These results have significant implications for space applications, particularly in LEO environments, where satellites experience rapid and extreme thermal cycling. The ability of the motor to maintain consistent performance in such a wide range of temperatures is critical to ensuring the reliability of satellite operations. Temperature-induced shifts in both impedance and phase characteristics highlight the need for careful thermal management strategies in the design and operation of space-based motors. To further evaluate the motor's performance, angular motion speed measurements were conducted at varying temperatures and excitation voltages. The purpose of these measurements was to simulate the thermal and electrical conditions expected in the low Earth orbit (LEO), where small satellites experience extreme temperature fluctuations. The results, shown in Figure 22, provide information on how both temperature and voltage influence the motor's average angular speed (RPM). Figure 15.4 Impedance– and phase–frequency characteristics of the motor under different temperature conditions. At temperatures below 0 \({}^{\circ}\)C, the motor shows a reduced angular speed across all voltage levels. For example, at 180 V\({}_{\text{P-P}}\), the maximum angular speed reached at \(-20\)\({}^{\circ}\)C is around 1400 RPM, while at \(-10\)\({}^{\circ}\)C, the speed is slightly below 1400 RPM. These lower speeds can be attributed to the increase in mechanical resistance and stiffness of the motor materials at subzero temperatures, as well as to higher electrical resistance. These conditions impede the efficiency of the motor, leading to lower rotation speeds. In the temperature range from 0 \({}^{\circ}\)C to 20 \({}^{\circ}\)C, the motor achieves its highest performance. At 0 \({}^{\circ}\)C, the motor reaches its maximum angular speed of approximately 1600 RPM at 180 V\({}_{\text{P-P}}\), the highest speed recorded in this set of experiments. The linear increase in speed with voltage in this range suggests that the motor is operating in an optimal thermal condition, where both mechanical and electrical properties are well balanced, minimizing resistance and maximizing efficiency. As the temperature increases to 30 \({}^{\circ}\)C and 40 \({}^{\circ}\)C, the motor's angular speed begins to stall at higher voltage levels. At 40 \({}^{\circ}\)C, for example, the motor reaches a maximum speed of approximately 800 RPM at 140 V\({}_{\text{P-P}}\), after which further increases in voltage do not result in a proportional increase in speed. This stall is likely due to thermal limitations, such as increased internal friction and material softening, which limit the motor's ability to sustain higher speeds at elevated temperatures. This behavior highlights the motor's sensitivity to thermal saturation, where further increases in excitation voltage do not yield improvements in angular speed. The combined influence of voltage and temperature on the motor's angular speed illustrates its operational efficiency under varying thermal and electrical conditions. At low temperatures, motor performance is hindered by increased stiffness of the material and electrical resistance, leading to reduced speed. On the contrary, at moderate temperatures, the motor operates at peak efficiency, achieving the highest angular speeds. However, at high temperatures, thermal effects such as material expansion and increased friction limit the speed despite the application of a higher voltage.