## 6 Conclusions  
An analytic model of the forming process of the STACER cylinder has been proposed to provide a general method for the design and production of a STACER from a theoretical level. A STACER finite element model has been established to simulate the mechanical characteristics and self-preservation performance during its gathering process by using finite element software. The effect of different radius dimensions of the top rod on the gathering process of the STACER has been studied. The influences of surface friction coefficient and acceleration direction on the gathered stability of the spring reel were analyzed. From this work, the following conclusions were drawn. 1. A different radius of the top rod affects the cone angle of the spring reel during gathering process. The large cone angle blocks the gathering process, and breaks the STACER. The optimum size of the top rod radius is 8.7 mm in this work. Local plastic deformation occurs at the riveting position when the radius of the top rod is 9.0 mm. When the radius of the top rod is 9.3 mm, the force on the top rod increases rapidly, which leads to the destruction of the spring reel after it is gathered. 2. The friction coefficient between the layers of spring reel is an important factor to effect the self-preservation of the STACER. When the friction coefficient is lower than 0.009, there is insufficient friction between the layers of the spring reel, and some layers move and deploy outwards of the storage barrel. When the friction coefficient is higher than 0.009, the spring reel can maintain a stable state. 3. Acceleration is another factor needs to be considered during the launching process of the STACER. When the acceleration direction is along the positive direction of X axis, the innermost layer near the top rod extends outward, and the gap between layers gradually increases. The friction decreases and some of the layers go beyond the innermost layer, and then exceed the top of storage barrel. Instead, only limited local areas appear in intermittent gaps when the acceleration is along other directions in the simulation. The STACER is in a stable state. Therefore, STACER should be installed without undertaking an acceleration along the positive X-axis direction at the riveting point during launching process. 4. The reliability and accuracy of the finite element model for simulating the mechanical characteristics and self-preservation performance of the STACER during the gathering process is verified by means of the experimental method. When the radius of the top rod is 8.7 mm, the tendency of the force on the top rod is similar between the simulation and test results. This provides a guidance for the further mechanical simulation of the STACER. 5. This study provides guidance for the design of all kinds of STACERs with different sizes and application conditions. For the diameter selection for the top rod, the radius of the top rod which equals the minimum end diameter of STACER is not suggested. It may cause serious deformation to the riveted part of STACER during the packaging process. For determining the friction coefficient,  
Figure 16: The comparison of finite element results and experimental data with the top rod load. in the deployment process, a large friction coefficient helps STACER to achieve self-protection. With the consideration of gravitational acceleration, the directions affect the self-preservation of STACER and it is sensitive to a certain direction. So it is suggested that STACER is required to be installed in the proper direction for gravitational acceleration during its transportation or launching processes. The following are available online at [[http://www.mdpi.com/1996-1944/13/7/1650/s1](http://www.mdpi.com/1996-1944/13/7/1650/s1)]([http://www.mdpi.com/1996-1944/13/7/1650/s1](http://www.mdpi.com/1996-1944/13/7/1650/s1)), Figure S1: The spring peel with mesh sizes of **(a)** 0.99075 mm, **(b)** 2.06864 mm and **(c)** 3.03555 mm, Figure S2: The force on the top rod with different mesh sizes in the gathering processes.