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.
B is 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.
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.
TANGENT VS. DIRECT SPOKES.
The subject of Tangent vs. 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 touched the outside circumference of the hub in one place, it would make two purely tangent spokes. (See cut.) As, for instance, a b and c d make all together four spokes, a f, b f, d e, and c e. If a spoke runs from any point, a, c, b, or d, to any point on the circumference of the hub between f and e, 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.
