Figure
2 shows data gathered along the 1 and 3 directions. A 3D model and the bent state of the TWS along the 1 direction are shown in Figure
2(a). When
and
, Figure
2(b) shows the influence of the displacement
on the output voltage from the TWS along the 1 direction. As the displacement
gradually increases from 1 to 20 mm, the peak output voltage first increases and then reaches a plateau. This is because increasing the displacement
can decrease the distance between the PTFE pellet and Cu electrodes and increase their contact forces. From [
22], increasing mechanical compression between the PTFE pellet and Cu electrodes causes an increased output voltage. However, due to material limitations and the size of the TWS, the output voltage saturates the sensor. Moreover, a leave-one-out cross-validation (LOOCV) strategy was used to fit the 1 model, and the detection accuracy and generalization performance of these models are shown in Figure
2(c). This confirms that the quadratic model has a high correlation coefficient of 0.99382 at all displacement values, with errors being less than 0.22% at displacement
, and a relatively higher error of 2.7% at displacement
. These errors may be caused by environmental vibration from the motor. Figure
2(d) shows the influence of the collision frequencies when
and
along the 1 direction. Evidently, the output voltage of the 1 direction is nearly constant when the frequency increases from 0.2 to 1.2 Hz. Frequency has little effect on the voltage output from the TWS. Figure
2(e) describes the influence of the collision height on the output voltage from the TWS along the 1 direction when
and
. Contrary to the case where
increases, the peak output voltage first decreases and then plateaus as the collision height gradually increase from 60 to 90 mm. This is because the displacement of the PEFT pellet along the 1 direction decreases as the collision height gradually increases. Using the LOOCV strategy, the detection accuracy and generalization performance of 1 model regarding the collision height are shown in Figure
2(f). The output voltage also fits well to a quadratic function of collision height with a high correlation coefficient of 0.96027. Together with 1 model regarding the displacement as shown in Figure
2(c), the quadratic models describing the TWS and simulating shaft motion suggest that the detection accuracy is sufficient to use the whisker in robotic applications. The data along the 3 direction are plotted in Figures
2(g)–
2(l). Note that, in contrast to data from the 1 direction, the falling edge is generated at peak output voltage values, as shown in Figures
2(h),
2(j), and
2(k). Therefore, the deflection direction can be determined using the output voltage. Similar data along the 2 and 4 directions are plotted in Figure S3. We observed that for all directions, the collisions associated with data sets correlate them with object distances. In addition, a silicone rubber joint is designed to provide damping and support the device. Table S1 and Figure S1 show how 3 silicone samples with different hardness affect the output voltage. One can see that the sensor is greatly disturbed by vibration when no silicone rubber is used. However, when a harder silicone is used for damping, the output value caused by environmental vibration will decrease. This means that the design of using silicone rubber provides TWS with more stable performance in practical applications. On the other hand, because the silicone rubber and spring can help support the whisker shaft when a TWS is placed horizontally, we can ignore the influence of gravity when the whisker shaft is forced by some external stimulus. As shown in Figure S2, there is almost no difference between the output voltage placed vertically and horizontally. The results show that the output voltage will be the same regardless of orientation. Consequently, a perceptual system based on TWS reveals technical abilities to navigation, local mapping, and object recognition.