MISCELLANEOUS MECHANISMS 411 
_ free-wheel ” bicycles being well known. In Fig. 671, A is a ratchet 
4 of special form connected to the hub of the driving wheel of the 
e. Cis a ring encircling A and forming part of the sprocket wheel. 
formed on A contain hard steel rollers B, which act as ratchets. 
@ recesses containing the rollers are of variable depth, and the rollers 
are pressed lightly forward towards the shallower ends of the recesses 
by light springs behind them. When C is driven forwards in the direc- 
tion of the arrow, the rollers are rolled up the 
slight inclines on A, and A, B, ard C are locked 
together ; but if C should stop, A will continue 
to move forward, or if A should tend to overrun 
C, it may do so because the rollers are then 
rolled back on the inclines and A is free from C. 
A slight modification of this gear is shown in 
Fig. 672, where the springs are spiral and are partly concealed within 
guide blocks behind the rollers, 
A form of friction ratchet, known as the awtoloc, has been applied in 
a number of ways. One application of this mechanism is shown in 
Fig. 673. A isa fixed case 
or cup which is mounted 
on a pin or stud, which 
also carries the separate 
levers B and E. Between 
the case A and the boss SZ 
H on B there is an an- 
nular space which contains o£, = 
LL“ fone i KER ~ rs 
two lugs FF formed on a7 Z| \ |} 
the lever E. The lever B Wize hee 
lies in the right-hand GENS 
between the lugs FF. Ne 
In the left-hand space Fic. 673. 
between the lugs FF there 
are two balls CC separated by a spiral spring D. The balls CC have 
bearings in a shallow groove in A and also on the boss H of B, but the 
surface of H in contact with the balls is not concentric with A, but is 
shaped so that the annular space containing the spring D and the balls 
CC gets shallower in both directions from the centre line XX. The 
object of the contrivance is to move the lever B through any angle, and 
then lock it in the new position automatically. In the position shown, 
the lever B is locked by the balls CC, which are wedged between A and 
H by the action of the spring D. If the lever E he moved, say upwards, 
the lower lug on E unlocks the lower ball, and the upper lug moves the 
lever B downwards, and as soon as the force actuating E is removed, the 
Spring again wedges the balls between A and H, so that no force applied 
to B will move it. 
Exercises XXV. 
1. A plane reciprocating cam has uniform motion and a stroke of 5 inches. 
The follower reciprocates at right angles to the line of stroke of the cam and in 
the plane of the cam. For the first 4 inch of the forward stroke of the cam the 
follower is at rest at the bottom of its stroke. For the next 2 inches of the 
cam stroke the follower rises 14 inches with uniform acceleration. For the 
