The rotation of friction wheel 1 about fixed axis D is transmitted through disk 2 with elastic tyre a to friction wheel 3 which has the same diameter as wheel 1 and rotates about fixed axis A. When the speed of wheel 1 changes, disk 2 tends to move vertically, but, since its axis is located at the middle point of the connecting rod of crossed-crank linkage ABCD, disk 2 is deflected from the vertical and is pressed against either wheel 1 or wheel 3, depending up on whether the speed of wheel 1 increases or decreases. Linkage ABCD consists of links 4, 5 and 6, and is suspended on springs 7. When disk 2 is thus deflected, the transmission ratio from wheel 1 to wheel 3 changes so that the speed of wheel 3 is maintained almost constant. Thus, upon variations in speed of driving wheel 1 within narrow limits, driven wheel 3 rotates at almost constant speed.
$3456$CF,G$