In this topic, we applied the Fmincon function to the optimum question when choosing the structure of a 7-bar bearing steel bearing, divided into groups of the same size, including group 1 (1, 2 bars), group 2 (3, 4, and 5 bars), and group 3 (6, and 7 bars) with three fixed head points and two bearing points. Using the Matlab software code, we have identified the structures of each group of steel bars corresponding to the radius of 1.564 cm, 3.509 cm, and 4.724 cm, respectively. Through this, we can identify the 1, 2, and 3 bars that are resistant to traction; the 3, 5, 6, and 7 bars that are subject to compression; and the 4 bars alone that are not subject to the action of the force. The results show that using the optimal method, we choose the different sizes, thicknesses, and volumes of the pipe so that it best suits the technical requirements of the paper, to avoid waste of raw materials, affecting the economic cost.

This article presents how to speculate, design and simulate a mechanical horse based on the point of view of the military man Khong Minh, a talented character in the work "Three Kingdoms" (author La Quan Trung). The behavior of this type of horse closely resembles that of a real horse. That is, it can walk, run, carry goods or people. It is made mainly of wood or steel. The authors speculated that Khong Minh placed a leaf spring in the belly of the mechanical horse. Soldiers just need to rotate so that the leaf spring twists, it will store energy in the form of potential energy. Then, it slowly unfolds, and the potential energy is converted into kinetic energy, transmitting motion to the mechanisms connected to the horse's legs. Finally, the mechanical horse lifted his leg and was able to walk. Despite such speculation, when recreating a mechanical horse, our team of authors used a battery-powered motor instead of leaf springs and gear transmissions as a pre-assembled transmission part in the belly of the mechanical horse. We design additional parts such as the head, tail, belly, legs, etc. to create a complete mechanical horse. The design goal of the author's mechanical horse is to clear people's doubts about the "wooden buffalo mechanical horse" in the literary work "Three Kingdoms". At the same time, this type of mechanical horse is also applied as an amusement ride for people in tourist areas and as a children's toy in the family.