Cycling art, energy, and locomotion

by Robert P. Scott

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 entire dependence 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 very similar 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.

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 England upon 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 frame b b, which is connected loosely, not rigidly, to the drum. By this arrangement the pressure is distributed evenly upon the three rollers d, 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 in this 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.”