The transmission efficiency should be high, the service life should be long, the structure should be simple, the manufacturing should be convenient, and the maintenance should be easy. For automobiles, since the output shaft of a cross-axis universal joint rotates at an uneven speed relative to the input shaft (with a certain angle), a double universal joint (or multiple universal joints) transmission must be adopted, and the two universal joint forks connected to the transmission shaft should be arranged in the same plane, and the angles of the two universal joints should be equal. This is very important. The angle of the universal joint should be minimized during design