Promotion of Machine and Mechanism Science (MMS) among young people worldwide is one of the missions of IFToMM. Conducting Student International Olympiads on MMS (SIOMMS) fully meets this mission and is considered as an essential tool for attracting talented youth to MMS as a science. The history of SIOMMS is approaching ten years. It is the right time to analyze the experience with such events. The article summarizes the experience of the first four SIOMMS, in terms of both organization and content. The topics that were included in the contest problems are described in detail. It is indicated which of the essential MMS topics were offered at each Olympiad. The article provides the texts of eight contest problems from the first Olympiad. Generalizations, conclusions, and recommendations are made regarding the procedure for conducting the Olympiads and preparing for them, which will be useful for future participants.

In 1898, Ernest Duporcq stated a famous theorem about rigid-body motions with spherical trajectories, without giving a rigorous proof. Today, this theorem is again of interest, as it is strongly connected with the topic of self-motions of planar Stewart-Gough platforms. We discuss Duporcq's theorem from this point of view and demonstrate that it is not correct. Moreover, we also present a revised version of this theorem.

This paper presents a six degree-of-freedom (DOF) real-time motion tracking system of measuring the position and the orientation for industrial robots in three-dimensional (3D) space. The proposed system is based on a typical Stewart platform design and utilizes six low-cost displacement sensors to monitor the motion of the Stewart platform. The advantage of the proposed system is its simple calibration and easy accessibility; the magnetic ball-and-socket joints used for rotational joints. With special measurement tools, the center of rotation of all twelve joints can be measured in 3D space at a glance. Following more than fifty measurements, the average root mean square (RMS) position accuracy error of the proposed device is less than 0.186 mm and the average of angular accuracy error is less than 0.160 °, making it suitable for monitoring the performance of industrial robot. A commercial robot is also tested by the proposed system to verify its usefulness.