Carbon brush spring is a kind of fixed force spring, which is made of stainless steel tape by a specific machine. When it is straightened by external force, the spring will naturally roll back and produce elastic force. However, to achieve our goal, we can return to our designated starting point after displacement. The advantages of constant force spring over traditional wire spring: all the strokes keep a certain amount of elasticity, the pre force stroke is short, that is, as long as the stroke is short, the required elasticity can be achieved, the original length is less than the wire spring, and the stroke is unlimited.