The mode of double-driving by differential or balance gear—so called because the power is divided or " balanced" between the two driving-wheels—employs an epicyclic train in which the two primary wheels are each connected directly or indirectly with one of the driving wheels of the tricycle, and also connected with each other through an intermediate loose train. One of the simplest forms of differential gear somewhat resembles an ordinary revers ing train ; one of the two facing wheels is fixed to the hub of one of the driving-wheels, which runs loose on the axle, and the other facing-wheel is fixed on the driving-axle. on the hub of which is fixed the other driving-wheel. Between the two facing-wheels a chain-wheel is mounted loosely on the axle, and this carries loose on a radial axis a bevel pinion-gearing per manently with both facing-wheels.
When the tricycle is running in a straight line, both driving-wheels are driven equally by the chain-wheels, the two facing-wheels meanwhile being drawn round by the intermediate pinion, which at that time is idle.
But when the tricyle travels in a curve, the inner driving-wheel revolves at a slower rate than the outer wheel, and consequently the outer driving-wheel is driven through the bevel. gear at a consequently higher speed, in whichever direction the machine is running, whether forward or backward.
As already described in regard to bicycles, there are two methods of driving a tricycle: Firstly, by rotary action, in which the power is applied either directly to a cranked axle carry ing the driving-wheels, or to a cranked pedal-axle connected with the driving-wheel axle an endless chain or other means; and. secondly, by lever-action, where the ',toyer is applied by reciprocating pedal-levers, from which the motion is communicated to the driving wheel axle through cranks and coupling-rods, or otherwise. The lever-action lends itself most aptly to obtain varying power ; but in speed the rotary action is superior. The reason would seem to be that in the lever-action the direction of force is changed so suddenly that in rapid pedaling a certain amount of back pressure is unavoidable.
Of direct-action or rotary tricycles. the simplest form has two driving-wheels mounted on the end of a cranked axle, and connected to it by clutches, the rider driving the axle direct. This arrangement simplifies the construction and reduces the working parts; but the high position of the center of gravity offers an objection to the stability of the machine.
The swinging, pedals are sometimes hung from the cranked axle, thus lowering the center of gravity, And rendering the machine more stable.
A successful lever-action machine is called the " Omnicycle," which is fitted with a vari able-power gear.
The pedal levers are connected by bands to two expanding setzments connected by clutches to the driving-axle, and to each other by a reversing apparatus, so that the forward movement of the one produces the backward movement of the other, thus the descending pedal raises the other ready for the next stroke.
The frames of tricycles are largely constructed of Nvehiless steel tube, and their contour and general arrangement vary with the different types of machine. Malleable-iron castings have been used in many of the solid parts.
The steering-gear of such tricycles. as have a single steering-wheel is usually the same as that of a bicycle, employing a transverse handle-liar; but another method, using a rack and is frequently adopted. The pillion is fixed to a vertical handle, mounted in bearings, so that it can revolve ; and the rack forms part of a light rod, the free end of which is con nected with an arm fixed on the fork of the steering-wheel.
In each different make of tricycle there is a certain position for the rider's seat, in respect both to the axle of the driving-wheel and also to the pedal crank-axle. so as to permit the rider to exert his power to the best advanta.g,e. The best position for the seat on a front-steer ing, tricycle is generally 11- in, in front of the driving-axle, and 7 in. behind the pedal-axle, this axle, therefore, being 83- in. in front of the driving-axle.
The above-described tricycles are types of those manufactured and used in England, where such machines find much more favor than in the United States.
The only form of tricycle which has been extensively made. and sold in this country is shown in Fig. 6. It is called the Surprise Columbia Tricycle." and has a 32-in. rear driving wheel, operated from the pedals by sprocket-wheels and a connecting chain.
There are two 26-in. front steering-wheels, journaled on the ends of a cross-bar or axle, forming part of the frame, adapted to be adjusted so as to vary the width of the running track as well as to be folded. to still further reduce the width, in order to enable the machine to pass through ordinary doorways. The width is variable, between 34 in. and 29 in. all over.