The subject of cranks and levers has been touched upon from a philosophical stand-point, but an ingenious squib in a maker’s catalogue on the subject has suggested the propriety of treating its mechanical features more fully. The squib referred to runs as follows:
“CRANKS VS. LEVERS.
“The question of a motive power for cycles is as old as the first idea of wheel riding. Inventors, after having persistently tried and abandoned every other known motor,—steam, electricity, etc.,—have made every effort to discover the best way of applying leg-power.
“While nine-tenths of the cycles have always been driven by cranks, in a few cases the attempt has been made to show that power could absolutely be created by the use of levers, and that if the power could be applied on one side only of the axle, avoiding the return stroke of a crank, the result would equal a man’s lifting himself over a fence by his boot-straps.
“In their eager pursuit of this one idea its advocates have lost sight of the fact that the question is of the economical use of the power we have, and that it is as impossible to create a power as to overcome the laws of gravitation. For hundreds of years the machinery of the world, practically speaking, has been driven by cranks. In this fact we have the testimony of the highest mechanical genius the world has known.
“Engineers agree that the crank is the only economical method of applying power—that it transmits to the driving shaft ninety-nine per cent. of the power applied. In no class of machinery except cycles is the attempt made to use levers where cranks could be used.
“Careful experiments have shown that the use of a lever is misleading, in that, while power can be converted into speed and speed into power, the development of either is at the expense of the other. It is at once evident that with levers we have more friction, more weight, and more complication than with cranks, and that absolutely more power is required, as the springs which are used to return the levers must be forced down at the expenditure of power which should be applied to the propulsion of the machine. Several years ago lever-power was tried in England on bicycles and tricycles and extensively introduced, but has been so generally abandoned that there is to-day no machine of importance so driven. The worst feature of the lever action, however, is that the movement of the foot does not become automatic, as is the case in the use of the crank. There is absence of regularity, and a consequent loss of momentum. A rotary motion is more natural to the feet, being more like walking, while a lever motion is like treading water while swimming, or like constantly climbing up stairs. Not only does the mechanical use of the legs require a regular movement, but it is better to use always the same length of crank, never varying the throw.
“A special set of muscles can be trained to such work as the use of the lever action; but such development is abnormal and at the expense of other parts of the body.”
There is little doubt in the minds of reasonable people that a good machine can be made either with cranks or levers; and this possibility makes it an interesting point in cycle discussion. It is hardly fair, however, to hold a maker responsible for matter written for the purpose of advertising his wares, nor do I wish to do so. The article above quoted puts, in unique form, the opinions of a large class of observers, and for that reason it is given here. I take up the lever side of the question simply because there is more to talk about on that side, and also perhaps for the reason that I have had large experience at considerable cost in experimenting on different forms of levers.
Some of the remarks about “creating power” are true, but might be applied equally well to some of our crank theorists.
To say that the machinery of the world is driven by cranks, is hardly tenable; even though the engine generally has a crank. But now, since we must reduce our comparisons down to the human motor, in combination with the crank of a bicycle, let us say the pitman rod represents the man’s leg. This rod has to push and pull, which a man cannot do with one leg; but for this you say he has two legs; admitting, then, that two legs represent the pitman, we are still out a fly-wheel and an evenly-running resistance. (See [chapter on “Connecting Link.”])
A great deal of the power of machinery is transmitted through pulleys and belts; now I take it that this is much more similar to some of the drum and lever machines than to a simple crank. There is, however, a form of lever and crank combined, of which I have spoken elsewhere, that is really worse than any simple form of either, but we have just as much right to say the crank ought to make it good as to say the lever makes it bad; if the crank is such a great cure for all evils, as the maker quoted seems to imply, it ought not be so bad in any combination.
There is no loss of power in pushing down a spring if it is only just strong enough to lift the leg, since the leg would otherwise have to be lifted by the expenditure of muscular energy. In using a spring we press down with a little more weight than is required to run the machine, so that a storage of power is the result which is given out in lifting the leg. In fact this is done to some extent in the crank machines; the rider not only puts enough power on each crank to turn the wheel, but also enough to lift the other leg; this is true at least when the rider is quite tired. Examples are known wherein a racer on long distances could no longer lift his legs, even with the aid of a spring, though at the same time, he still had strength enough left to propel the machine. In fine, this difference between the crank and spring lever is that in the former, a little extra power is exerted to lift the other leg, while, in the latter, energy is stored to be used in raising the same leg.
In a perfectly fresh man I have found, by the registers of the cyclograph, that the rider lifts all weight from a returning crank, but this does not happen when he becomes tired. Evidently, if the spring is strong enough to more than lift the leg, a loss of power will result, since the rider would have to hold it in check even in coming up in order to keep it from stopping with a bang, as is sometimes noticed when he jumps from a treadle machine. The winding and unwinding of the spring involves no loss of power except in heat incident to motion and imperfect elasticity, which is quite small. This loss from heat within the molecular structure, I am constrained to think, is not what is popularly meant by loss of power in springs.
Coming back to our quotation, true, in England levers have been tried and expunged. A prominent American, I believe, assisted some little in enlightening our too susceptible English brethren on the subject, yet some attempts have been made with them in this country which no fair person can call unsuccessful.
A little printer’s ink will answer the last sentence of our quotation. Simply change the words “lever-action,” and substitute “cranks,” and you will have the following: “A special set of muscles can be trained to such work as the use of cranks, but such development is abnormal and at the expense of other parts of the body.” So the reader can see how a little slip in the type would have changed the whole argument. This discussion could be continued with great interest to both sides if we could only find in some maker’s catalogue of lever machines an attempt to “down” the crank machine on general principles. As it is, it must close for lack of antagonism in so far as broad principle goes.