CHAPTER VI.
GRAPHIC ILLUSTRATION OF THE APPLICATION OF POWER TO CYCLES—KINEMATICS.
The manner in which the construction and general arrangement of the driving mechanism, the road surface, and other conditions control the application of power is a curious study. In connection with it I have made an instrument to illustrate the same graphically, which, for the sake of a name, we will call the “Cyclograph,” an engraving of which will be found below.
The Cyclograph.
A frame, A A, is provided with means to attach it to the pedal of any machine. A table, B, supported by springs, E, E, has a vertical movement through the frame A A, and carries a marker, C. The frame carries a drum, D, containing within it mechanism which causes it to revolve regularly upon its axis. The cylindrical surface of this drum, D, is wrapped with a slip of registering paper removable at will. When we wish to take the total foot-pressure, the cyclograph is placed upon the pedal and the foot upon the table. The drum having been wound and supplied with the registering slip, and the marker C with a pencil bearing against the slip, we are ready to throw the trigger and start the drum, by means of a string attached to the trigger, which is held by the rider so that he can start the apparatus at just such time as he desires a record of the pressure.
The following are a few sample sections cut from registering slips illustrating some of the points discovered in these experiments. Only a few strokes of the crank or lever can be shown; it is evident that great space and expense of reproduction would be required to give the entire record for even a small part of a mile. It will be understood, I think, without further explanation, that these curves show the extent and variation of pressure of the foot upon the pedal in order to drive the respective machines under circumstances named and described by the figures and thereafter.
52-inch Ordinary; race-track; getting up steam.
52-inch Ordinary; race-track; speed, eighteen miles per hour.
52-inch Ordinary; race-track; speed, ten miles per hour.
52-inch Ordinary; race-track; speed, ten miles per hour.
52-inch Ordinary; up hill, grade, one foot in twenty-five; speed, about eight miles per hour.
52-inch Ordinary; starting up hill.
52-inch Ordinary; up hill, grade, one foot in ten; stalled at four miles per hour.
52-inch Ordinary; up hill, grade, one foot in twenty-five; curves of both pedals superposed.
52-inch Ordinary; back pedal; down hill, grade, one foot in twelve.
Rear-driver Rover type, 54-gear; up hill, grade, one foot in twenty; speed, nine miles per hour.
Rear-driver Rover type, 54-gear; up hill, grade, one foot in twenty; continuation of No. 10.
Rear-driver Rover type, 54-gear; up hill, grade, one foot in seven; speed, ten miles per hour.
Lever rear-driver, 30-inch wheels, gear about 50; up hill, grade, one foot in twenty; speed, eight miles per hour.
Lever rear-driver, 30-inch wheels, gear about 50; up hill, grade, one foot in twenty; speed, twelve miles per hour.
Lever rear-driver, 30-inch wheels, gear about 50; up hill, grade, one foot in twenty; continuation of No. 14, over top of hill.
A six-inch crank was used upon the machines in these experiments, and the lever action was such as to be comparable to a fifty-inch gear. The height of a point on the curve shows the extent of and variation in power upon the pedal, and the translation from left to right the time. In consequence of the limit of pressure occurring but once in each stroke, the number of undulations determines the speed, since it would show the number of strokes in a given time, and we know the number that make a mile.
The number of pounds’ pressure at any point on a curve is shown by the figures upon the perpendicular line, as, for example, in [No. 1] the apex of the curve just to the right of the scale is about even with the hundred-and-fifty-pound point; this pressure was maintained for a very short space of time, since the curve travels a very short distance to the right at this point; in other words, it is quite sharp at the top.
Stronger springs were used on the Cyclograph in testing the safeties, as I found myself liable to compress them beyond their limit; hence the scales must be closely observed in making comparisons. Among the interesting results noticeable in these experiments I find, for instance, in Nos. [3] and [4], an abnormal deviation in the height of the curves at the same speed upon the same track at nearly the same time, though running in opposite directions. Finding this strange difference of some fifty pounds in pressure, I noticed an almost imperceptible breeze against me in the one, and in my favor in the other, direction.
[No. 12] illustrates how a hundred-and-fifty-pound man gets up a pressure of two hundred and forty pounds presumably by a ninety-pound pull on the handle-bar.
In [No. 9] we see how one hundred and fifty pounds pressure is applied in back-pedalling down a grade of one foot in twelve. That the curve would not be very regular is easily impressed upon the mind of the average rider.
One part of curve (not shown), of peculiar contour, terminated experiment [No. 9] at a rut a little farther down the hill, with dire results to the operator and provoking influence upon the running gear of the ’graph, which has been making some erratic curves of its own, now and then, ever since.
Comparing Nos. [5], [10], and [13], the curve of the lever machine (13) indicates that, while pressure is not so great as in the others, it is held for a longer time, shown by the greater height and sharper tops to the curves of the crank machines.
The short cross-lines about three-fourths up on the left sides of the undulations in Nos. [10], [11], and [12] designate the points at which the crank crosses the perpendicular at the top. There is quite a pressure, and it is a little odd that it should be found at this point; it can only be attributed to ankle-action back of the natural dead centre.
In [No. 6], and to some extent in all the others, observe the jagged appearance in the general advance of the curves, which must be due to vibration: these results were all obtained upon tolerably smooth roads, mostly in Druid Hill Park, Baltimore. [No. 6] was taken upon a road perhaps a little rougher than the track around the lake, but still upon an unusually smooth surface, and it was a surprise, not to say an alarming discovery, that this vibration should occur under such circumstances.
The lake track, upon which results [2] and [3] were found, was in perfect condition, smooth as a surface-plate, and without the customary sprinkling of pebbles so common when dry weather has loosed the settings of these tiny obstructions and suffered them to roll out upon the roadway; yet these figures show the saw-teeth, and I have been unable to find a road smooth enough, or jointed machine frames and springs good enough, to make unwavering symmetrical lines. These little deviations in the curves always seem to show themselves to the extent of several pounds in height in spite of all alleviating conditions, suggesting that we have much to strive for in the construction of the ideal wheel free from all concussion. In order to judge accurately of the total amount of power to turn the wheel, we have to consider the register of both pedals superposed, as in [No. 8], but the curve made upon one generally answers all purposes. The possibilities in this study are unlimited, and, with a perfectly-accurate instrument, it strikes me, the results of much more definite bearing than those acquired in the silly practice of testing machines by the strength of men.
I have refrained from giving any tests as to the comparative power required to drive machines of the same type and of different manufacture, differences being liable to result from a bad condition of the machine, such as the want of oil, or from happening to get hold of an unusually bad sample, making the liability to do injustice too great. The writer does not feel himself called upon to judge of or express differences in quality of workmanship in general, if for no other reason than that by the time the matter goes to press, such merits or defects as he might have discovered may change. Workmanship does change, principles never can; and, what is more, the hypotheses and conclusions in regard to principles, treated of in this or any other book, are always open to contradiction; if injustice is done to any maker of wares in a matter of principle, said maker always has a remedy in defence, and if he can disprove assertions made his justification is complete, whereas if a mistake of fact is recorded, such as the operation of a certain machine, and the machine upon which the alleged fact is based happens to disappear, the party interested is denied a just remedy. There are of course certain criteria of good workmanship, and the same should be touched upon in order to teach the reader how to judge of it; but beyond this no writer should be allowed to go, unless at least he has been paid for advertising competing wares at regular rates.
The cyclograph attached to the revolving pedal shows the total amount of pressure required to do a certain work on a machine; but if it is desired to ascertain the track resistance or the friction of parts alone, it is necessary to so place the instrument as to register the tangential resultant in turning the crank, taking no note of any power thrown away by indirect application; that is, if we wish to register the circular or tangential resultant, the cyclograph is attached by its frame rigidly to the crank or lever of a cycle, and the revolving pedal, which has been detached, is hung upon the spring platform. This last arrangement is used in experimenting to ascertain the extra power available by ankle-motion, as will be shown hereafter.