CHAPTER XIX.
CRANKS AND LEVERS AND TANGENT SPOKES.
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 tocreatea 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 whichare 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.”
“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 tocreatea 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 whichare 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. (Seechapter 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 theotherleg, while, in the latter, energy is stored to be used in raising thesameleg.
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 willresult, 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.
As to the construction of crank machines, the subject is so familiar to every one, and the device is so simple, that it is impossible to write much of an essay on it. With regard to levers, however, the subject is inexhaustible. The most salient features claimed for the clutch machines now in the market are, first, non-dead centre,—that is, even, continuous power; second, entire rest of the legs when power is not required. The objections are chiefly, first, insecurity and entiredependence on the brake found in the absence of all back pedalling; second, non-support of the legs, springs being insufficient to sustain their weight. To the above objections appertaining to the lever and clutch machine, a third may be added,—viz., the complexity of parts, liability to breakage, and danger of accidents therefrom. At one time the advantage of safety was found in the clutch machine almost exclusively, but at the present time we have complete safety elements in certain forms of crank-wheels.
Much difficulty has been experienced by makers of lever cycles in finding a suitable clutching device, a difficulty with which most of the experience the writer has had is concerned. In conducting experiments in this line I have found that the rattle of the old ratchet was annoying, and it was quite a problem in my mind why makers used them; but any one who undertakes to make a bicycle clutch will soon discover the reason, though at what cost “deponent sayeth not.” A neophyte in the bicycle experimenting ranks might justly suppose that the matter of clutches is a well-developed art in mechanics; to a certain extent it is, but not in the direction he will need. Clutches may be divided into three classes,—first, the common ratchet and pawl, either spring or gravity; second, the ratchet and friction pawl; third, surface-friction clutches proper. The first two grip on corrugated surfaces, the last on a perfectly plain or smooth surface. The first class rattles according to the pressure on the pawl or the weight of the same, and also to the amount of drop. The second class rattles only under certain conditions; that is, when both ratchet and pawl are in motion in the same direction, one moving a little faster than the other. The third class is entirely noiseless. Let us pass over the first class, as being familiar to everybody. The second class is not so well known and has never been used in any of the arts in this country so far as I know, except as recently applied to bicycles. This clutch is verysimilar in appearance to a regular ratchet, the difference being that in the former the pawl is held out of contact by friction against some of the moving parts, and when the motion is reversed the friction in a certain direction throws the pawl into action. A good mechanic would have hardly conceded such an arrangement as practicable in any machine, much less in a bicycle, for the reason that when the motion is reversed the pawl plunges into the teeth with so much force that damage would be supposed to result. Several patents are registered in England upon the noiseless ratchet; they are all alike in general principle, but it is due to the energy of an American maker that it has been made a success in cycle construction, and I am inclined to think it is the first time such a ratchet has ever been used to any extent in any kind of machinery.
Noiseless ratchets.
Noiseless ratchets.
As to the third class of clutches, much of interest can be said for the benefit of those particularly concerned. “A friction clutch” to mechanics is a familiar term, since the name is applied to all pulley clutches, that grip on a smooth surface. Many of these clutches are a success for the purpose for which they are intended. The most common form used on machines where the requirements are similar to those of a cycle, is the “Roller.” The cycle experimenter nearly always strikes upon this clutch first, and with sufficiently good reason. It has been adopted in many arts, and is used in Englandupon tricycles in combination with cranks, with moderate success, but just here allow me to call attention to a cardinal difference in the requirements of a clutch as used on crank tricycles and successfully in the arts heretofore. In the crank-clutch cycles the clutch is used for the purpose of detaching the cranks from the spindle when the machine requires no driving, as in running down grade, but when once the clutch is gripped, it remains so till further power ceases to be required. Now, this is also just the action of all belt-pulley clutches, and between such action and that required in a lever-clutch cycle the difference is exceedingly conspicuous. In the crank-clutch cycle, as in other uses, the immediate solid grip is a matter of little concern; if a half turn of the parts takes place before clutching, it does little harm, since it is so small a fraction of the entire number of revolutions to be made before the grip is released. But if a grip is to be taken at every down stroke of the foot, as in a lever-clutch cycle, the least slip or lost motion is fatal.
This incessant clutching action, together with the great weight the parts have to sustain, and the repeated concussion of one piece upon another under this weight, makes up a combination of disturbing elements which will cause mischief against which it is almost impossible to provide.
In a form of roller-clutch I have tried, the inner frame or carrier is made loose upon a spindle.
In the drawing herewith annexed we have first a spindle in the centre, then a little open space around it, and then the clutch frameb b, which is connected loosely, not rigidly, to the drum. By this arrangement the pressure is distributed evenly upon the three rollersd,d,d, outwardly at three points against the casing, and in no event is the work done by a single roller. This device worked as well as any of this class I have tried; but the patterns are for sale at a very reasonable price. The main trouble I found inthis contrivance and all other roller clutches was, that the great pressure disintegrated the oil, making a paste that would cause the rollers to slip in spite of everything.
If it were not that another American, a cycle-maker, has apparently made a success of a roller-clutch, I should be tempted to warn all experimenters against it as a thing that “stingeth like a serpent and biteth like an adder.”
Loose centre roller-clutch.
Loose centre roller-clutch.
Under a bench in a shop not far from the geographical centre of England may still be found about a bushel of friction-clutches of various and ingenious forms, which future historians in the art will find very interesting. Should any one wish to enter the arena as a searcher for the true friction-clutch, let him first examine these specimens, and he will start several years ahead. The nearest approach to a success which the writer has fallen upon is illustrated below for the purpose of helping those who may wish to carry on the search, or experiment in clutch-cycles,—if any should think it worth while in view of the alleged success of the American above referred to. The clutch illustrated below was contrived by a fellow-laborer in the field.The drawing represents the device in a crude form; some improvements having been necessary to complete it.
Bis a cog-wheel within another,A, the latter fast to the wheel-hub, and the former to the clutch-drum. A wedge,E, follows between the wheels, whence it will be seen that they can revolve, in relation to each other, in one direction only.
Scott wedge-clutch.
Scott wedge-clutch.
For those who wish to study this question more minutely, Kempe, on link motion, will be found a valuable work in connection with the construction of levers in any art, when it is desired to obtain a motion in a straight line from an oscillating or circular.
In the way of conclusion, reverting to the possibilities of direct application of these remarks to the actual purchase and use of cycles, I wish to say, in regard to the mechanical difficulties in this matter of lever and clutch machines, that so long as the use of oil is necessary, I have very grave doubts if a thoroughly satisfactory, noiseless friction-clutch for use on cycles will ever be invented.
The subject of Tangentvs.Direct Spokes, or Direct vs. Partial Tangent, is one on which so much has been written and said within the last few years that it is probably well understood in the main by all enthusiastic wheelmen, but a few points may not come amiss to the beginner. In the first place, there is no such thing as partial tangency. A tangent spoke is tangent, and that is all there is about it. A tangent is a definite thing, and means a line normal to a radius at the circumference; at least, we can accept this definition as well enough suited to the cycle art. And, in speaking of tangency, we ought rather to say tangent hub than tangent wheel, since the spokes are not tangent to the rim of the wheel, but to the hub. All cyclists know very well, nevertheless, what is meant by partial tangency in the cycle art, and I will therefore use the term. If a long spoke went straight from one point in the rim to another nearly opposite, and just touchedthe outside circumference of the hub in one place, it would make two purely tangent spokes. (See cut.) As, for instance,a bandc dmake all together four spokes,a f,b f,d e, andc e. If a spoke runs from any point,a,c,b, ord, to any point on the circumference of the hub betweenfande, it will not be a full tangent spoke. The distinctive characteristic of a full tangent spoke is that, when the force tending to revolve the wheel is applied, it pulls from the point on the hub which would recede most rapidly from that point in the rim to which the other end of the spoke is affixed. Hence, the common expression that “a tangent hub gives a direct end-pull on the spokes;” but so does any other hub, if the spoke is swivelled into it. With a direct spoke screwed into the hub, the weight of the man is sustained by a direct end-pull, and a slight power is transmitted to the rim by the resistance to flexure or bending in the spoke tending to revolve the wheel, and it will be found in practice that any hub with a direct spoke will turn independently of the rim far enough to increase the distance slightly between the ends of the spokes so as to really make an end-pull as in the tangent spoke, but evidently the hub must revolve a great way in order to increase the length a very little. Here comes in the advantage of the tangent spoke, for, in order to turn the hub within the rim, the spoke has to stretch an amount equal to the distance a point on the circumference of the hub moves. To represent this in popular terms, if the hub turns one-eighth of an inch, the spoke has to stretch that amount if tangent, whereas the necessary increase in length of the direct spoke is almost imperceptible.
Tangent spokes.
Tangent spokes.
One point must not be forgotten in this matter, which redounds to the credit of the absolute direct spoke. It is that the driving strain passes through every spoke from the hub to the rim, whereas, in a tangent or partial tangent spoke, the strain is resisted by only one-half of the entire number. This defectis partially remedied by the late plan of soldering the spokes together at the points of crossing, this binding together being what really makes the tangent spokes so strong in resisting buckling, to which they were very liable before the soldering process was used. I am inclined to think that the midway or partial tangent hubs are the best, as they seem to combine all of the possible advantages, but the plan of crossing the spokes just once is, in the light of my experience, very bad, as it seems to combine the faults of both with the advantages of neither; they should be more nearly full tangent than direct if varied from the midway position at all. The small eighteen- or even thirty-inch wheel is good enough, if well made, with either direct or tangent hubs, especially in the one not used as a driver.
Old bone-shaker wheel.
Old bone-shaker wheel.
The soldering of the spokes together, and other difficulties in the way of screwing them into tangent hubs, has led makers to adopt the plan of screwing them into the rim; this seems unavoidable, but is not very desirable, if for no other reason than that the wheel getting wet, the screw threads are apt to rust off and strip. With brass, aluminum, or bronze nipples,however, this difficulty can be to a great extent overcome.
Tangent wheels are as old as the industry of cycling. Starley, of Coventry, is said to have experimented and shown, many years ago, that a tangent wheel with silk spokes would resist the revolving strain on the hub equal to a direct wire spoke, and theScientific Americangave an illustration of a tangent hub in their issue of September 1, 1877.
The cross bar in the old bone-shaker made practically two tangent spokes, and pulled from the rim, so to speak, as will be noticed in our essay on hobbies.