# An Orthogonal Wheel Odometer for Positioning in a Relative Coordinate System on a Floating Ground
## 4 Discussion  
As far as we know, previous studies have not focused much on floating surfaces, such as decks. For the wheeled positioning of robots, a gyroscope is the current, preferred method used for the angle measurement in terms of economy and practicality. The usual odometer system does have the biggest problems with turns and orientation changes. However, our positioning system is a mechanical structure design, and the calculation of the position when turning is mainly dependent on the radius of rotation of the structure. This is a fixed value, and as long as the radius of rotation is accurate, the error tends to zero. There is no sensor like the gyroscope: the more turns, the greater the angle deviation. Different from other commonly used odometers, the error of self-developed orthogonal wheel odometers fundamentally depends on whether the rotation radius and our orthogonal wheel radius are accurate, as well as the accuracy of the encoder to read the orthogonal wheel mileage. Compared with the orthogonal wheel positioning system developed by ourselves, both LiDAR and gyroscopes have their drawbacks. The use of gyroscope is usually limited to the fixed plane based on the world coordinate system. With the increase in the gyroscope angle, the error also increases. In order to ignore the angle cumulative error of the gyroscope, the influence on the positioning error is minimal only in the case of a small number of turns. Laser positioning of LiDAR [23] is similar to the positioning mode of HTC VIVE used in the experiment. Although it has very high positioning accuracy, it has high requirements for the environment. In the process of LiDAR positioning, it is  
Figure 34: (**a**) The angle of chassis coiling around pitch and roll axis. (**b**) The error curve of orthogonal wheel relative to HTC VIVE. Figure 33: (**a**) The motion curve of the orthogonal wheels in irregular motion with the mobile floating platform. Compared with the actual curve, the orthogonal wheel positioning system has a good positioning effect relative to the moving path of the mobile floating platform. (**b**) Motion curve of gyroscope positioning along with irregular movement of the floating experimental platform. With the accumulation of angle errors in the process of motion, the obtained motion curve becomes more and more yaw. necessary to scan the surrounding environment and then match the boundary on the map to achieve the positioning effect. However, on a wide deck, it is hard to scan the boundaries we want, and it is even harder to locate them when there are dynamic obstacles. So LiDAR has its drawbacks, especially in the case of wide decks with unclear boundaries or sea fog. This new positioning technology needs to have accurate positioning accuracy and adaptability to floating environment. In view of the floating motion environment and the desired positioning task, the orthogonal wheels positioning sensor system designed by us can achieve a satisfactory positioning effect in this kind of environment. According to the experiment in the third chapter, we can understand that the positioning effect of the orthogonal wheels positioning system can achieve a very high positioning accuracy during the movement of a certain distance, and the positioning error can reach within 0.025 m. It can be seen from the random comparison curve that the positioning curve of the orthogonal wheel positioning system is basically consistent with that of HTC VIVE, and the maximum error is 2.43 (\(\pm\)0.075) cm in the process of moving. The RMSE of the positioning system on the floating platform is 1.51 cm. However, the positioning curve of the positioning system using gyroscope deviates more and more with the progress of the movement. This is because the orthogonal wheels are driven by design, and the positioning mode of the orthogonal wheel positioning system is not affected by the error caused by rotation like the gyroscope.