<Li> γ 2 (\ displaystyle \ gamma _ (2)) the angle of rotation for axle 2 </Li> <Li> β (\ displaystyle \ beta) the bend angle of the joint, or angle of the axles with respect to each other, with zero being parallel or straight through . </Li> <P> These variables are illustrated in the diagram on the right . Also shown are a set of fixed coordinate axes with unit vectors x ^ (\ displaystyle (\ hat (\ mathbf (x)))) and y ^ (\ displaystyle (\ hat (\ mathbf (y)))) and the planes of rotation of each axle . These planes of rotation are perpendicular to the axes of rotation and do not move as the axles rotate . The two axles are joined by a gimbal which is not shown . However, axle 1 attaches to the gimbal at the red points on the red plane of rotation in the diagram, and axle 2 attaches at the blue points on the blue plane . Coordinate systems fixed with respect to the rotating axles are defined as having their x-axis unit vectors (x ^ 1 (\ displaystyle (\ hat (\ mathbf (x))) _ (1)) and x ^ 2 (\ displaystyle (\ hat (\ mathbf (x))) _ (2))) pointing from the origin towards one of the connection points . As shown in the diagram, x ^ 1 (\ displaystyle (\ hat (\ mathbf (x))) _ (1)) is at angle γ 1 (\ displaystyle \ gamma _ (1)) with respect to its beginning position along the x axis and x ^ 2 (\ displaystyle (\ hat (\ mathbf (x))) _ (2)) is at angle γ 2 (\ displaystyle \ gamma _ (2)) with respect to its beginning position along the y axis . </P> <P> x ^ 1 (\ displaystyle (\ hat (\ mathbf (x))) _ (1)) is confined to the "red plane" in the diagram and is related to γ 1 (\ displaystyle \ gamma _ (1)) by: </P>

Where is the universal joint on a truck