Bell Crank
Bell Crank
Bell Crank
APPARATUSBell crank lever apparatus, slotted weights, spring balance and pointer.
THEORY-
A bell crank is a type of crank that changes motion through an angle. The name
comes from its first use, changing the vertical pull on a rope to a horizontal pull on
the striker of a bell, used for calling servants in upper class British households. The
fixed point of the lever about which it moves is known as the fulcrum.
The bell crank consists of an "L" shaped crank pivoted where the two arms of the L
meet. Moving rods (or ropes) are attached to the ends of the L arms. When one is
pulled, the L rotates around the pivot point, pulling on the other arm.
Changing the length of the arms changes the mechanical advantage of the system.
Many applications do not change the direction of motion, but instead to amplify a
force "in line", which a bell crank can do in a limited space. There is a tradeoff
between range of motion, linearity of motion, and size. The greater the angle
traversed by the crank, the more non-linear the motion becomes (the more the
motion ratio changes).
According to law of moments When an object is balanced (in equilibrium) the sum of the clockwise
moments is equal to the sum of the anticlockwise moments.
Applications
Aircraft
Bellcranks are often used in aircraft control systems to connect the pilot's controls
to the control surfaces. For example: on light aircraft, the rudder often has a
bellcrank whose pivot point is the rudder hinge. A cable connects the pilot's rudder
pedal to one side of the bellcrank. When the pilot pushes on the rudder pedal, the
rudder rotates on its hinge. The opposite rudder pedal is connected to the other end
of the bellcrank to rotate the rudder in the opposite direction.
Automotive
Here in this experiment we have to check the moment of a force about the various
point on the lever and that moment must be equal to the spring force multiplied by
the fixed distance d. The distance d in this experiment is fixed and equal to seven
inch.
So we have to verify
Moment, M = W * D = s * d
PROCEDURE1)
2)
3)
4)
5)
6)
OBSERVATIONSS.no
Weight
Distance
Moment
W kg
D inches
M=WxD
Spring
force
S(kg)
Calculat
ed value
of S
%error
(S1S)/S1
S1=WD/
d
X 100
1.5
1.28
21.8
1.17
17.2
0.75
11
8.25
1.16
14.5
W D
d
(N)
%Error =
S ' S
100
S'
RESULTFrom the values obtained above, its clear that the observed and calculated values
obtained for the value of spring force are nearly equal and within the permissible
experimental error limits.
Hence the Law of Moments has been verified