Cardan drive. Old cake

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Cardan drive = BMW. Yet?

Well, no longer in the meantime, but still in our collective memory.

Between 1928-1929 suddenly some 15 brands of motorcycles with cardan drive appeared. And all those constructors had come up with the same idea because by that time the belt drive was really a passing station and because the then roller chains had about the life of a calico cat in a pitbull kennel. The once legendary FN (Fabrique Nationale d'Armes de Guerre, the main source of income was the manufacture of war weapons. Two-wheelers were just a side issue) not only provided its four-in-line motorcycles with a cardan drive, it did the same with the ordinary bikes that the company made.

Low maintenance and clean

A cardan shaft transmission has a long service life, is clean and requires almost no maintenance. And we don't actually use the name correctly. We talk about it as if it is the entire drive from the output shaft of the gearbox to the rear wheel. But actually the cardan is a cross piece in a shaft transmission which makes it possible to have a 'kink' in the drive while it is rotating. The phenomenon is a tight 500 year or so ago devised by the Italian philosopher / mathematician Cardano. That good man designed a compass suspension so that the compass always remained horizontal no matter how badly the ship stumbled over the waves. One ring was on the compass edge with two pins. The second ring was on the first ring with the pins 90 turned degrees.

Without ship and compass

A little later we found that approach again at the universal joints where the ship and the compass were simply left out. Those universal joints were pretty hard to make until WWII. The so-called 'Hardy discs' were then used as an intermediate form. They were rubber or canvas discs with four holes in them. The pins of the output shaft of the gearbox protruded into two holes. The pins of the secondary drive shaft protruded into the holes offset in the 90 degree. The flexibility of the rubber disc makes a slight angle of rotation possible.

We are talking about low power and limited angular rotation due to the small ferry travel. The Hardy disk had the advantage that it properly damped transmission shocks. But as the powers increased and the widening became greater, such a hardy disk hit its limits. The universal joint evolved. The torsionally rigid transmission received spring-loaded, round cams to handle transmission shocks and rubber transmission dampers were mounted in the rear wheel hubs.

Now with slider!

The addition of a slider in the axle construction not only made dismantling and assembly easier, but also compensated for the - relatively small, yet - length change of the axle due to the difference in pivot point between bucket output and rear fork bearing. And was everything okay then? No, not. A single universal joint runs 'unanimously'. That is - long story short - through the corner distortion. This can be compensated by 'doubling' the universal joint. The last axis then rotates nicely at a constant speed. If such a double universal joint is implemented as a whole, we call it "gay magnet".

Turned teeth

And then we come to the right angle transmission in the rear wheel. In the past, bevel gears with straight teeth were used for this. That drive made a lot of noise and had its limitations in terms of power transmission. Therefore, other tooth shapes with curved flanks were developed. The small gear (the pinion) and the large one (the crown wheel) are a match, a very precisely coordinated whole.

Not maintenance-free, low-maintenance

Lubrication is important for cardan transmission. The type and amount of oil are not something of 'about'. The prescribed amount and type are of vital importance. The rubber sleeve around the hinge point must also be intact. Riders of older fat Guzzies and relatives disassemble the cardan annually for inspection and possibly to lubricate it. And that is a nice job before the winter break starts.

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