02-03-2019, 01:18 PM
Tony \ Denis
If you think of it like a classical lever, force is multiplied by making the distance from the fulcrum to the load small (at the expense of distance the load is moved). Halve the distance, double the force. In the case of constant torque on the cross bar you get maximum movement, minimum force at the magic 90 degrees. In fact in a frictionless incompressable system it approaches infinite just before it cams over (as the effective movement of the cable approaches 0). In the real world (on your Austin) the total mechanical advantage between the pedal and the brake shoe are balanced against enough travel to overcome the cable stretch, losses in joints and the need to move the shoes a certain distance.
The reality is you want to minimise the "force" on the cable component, to minimise the loses from the elastic properties of the cable. This is done by having the levers at 90 degrees to the cable (and why the leaver at the cross bar is longer than the lever at the hub)
Its a technicality really but it's worth thinking about.
Cheers, Mark
If you think of it like a classical lever, force is multiplied by making the distance from the fulcrum to the load small (at the expense of distance the load is moved). Halve the distance, double the force. In the case of constant torque on the cross bar you get maximum movement, minimum force at the magic 90 degrees. In fact in a frictionless incompressable system it approaches infinite just before it cams over (as the effective movement of the cable approaches 0). In the real world (on your Austin) the total mechanical advantage between the pedal and the brake shoe are balanced against enough travel to overcome the cable stretch, losses in joints and the need to move the shoes a certain distance.
The reality is you want to minimise the "force" on the cable component, to minimise the loses from the elastic properties of the cable. This is done by having the levers at 90 degrees to the cable (and why the leaver at the cross bar is longer than the lever at the hub)
Its a technicality really but it's worth thinking about.
Cheers, Mark