To find the braking torque, pulley 1 is mounted on the engine or motor shaft. Shoes 2 and 3 are held against pulley 1 by means of tie-rod a and spring 4. If spring 4 is tensioned so that pulley 1 tends to rotate the whole system, then cord f is pulled taut and it turns lever 5 about axis 0. At this, link 6 spreads levers b and k of shoes 2 and 3. This reduces the frictional force moment which becomes equal to M = Pd + Td₁ , where T is the tension of the cord. By regulating spring 4, tension T should be reduced to a minimum and point B located as close as possible to the axis of the brake pulley. Under these conditions, the quantity Td₁ can be neglected and the braking torque can be taken equal to M=Pd .
$471$SL,M$