Iso-elastic
Encyclopedia
In engineering, iso-elastic refers to a system of elastic
and tensile
parts (springs and pulleys) which are arranged in a configuration which serves to isolate physical motion at one end from affecting the same motion at the other end.
This type of device must be able to maintain angular direction and load-bearing over a large range of motion.
The most prominent use of an iso-elastic system is in the supporting armature of a Steadicam
.
The Steadicam arm is used to isolate a film or video camera from the operator's movements.
Steadicam arms all work in a fashion similar to a spring lamp since each arm has 2 sections (similar to and labelled like a human arm), both the upper and fore-arm sections consist of a parallelogram
with diagonal iso-elastic cable-pulley-spring system. The iso-elastic system is tensioned to counteract the weight of the camera and steadicam
sled. This tensioning allows the camera and operator to move vertically and independently of each other. For example as the operator runs, the bouncing of his body is absorbed by the springs, keeping the camera steady. The arm also has unsprung hinge
s at both ends of each arm allowing it to bend in the horizontal plane (just like your elbow, not like a spring lamp).
To understand how an iso-elastic system works, we must first understand how springs work. The tension
(elastic force) in a spring is proportional to its extension according to Hooke's law
. This means that if a weight is hung on a spring it will oscillate with simple harmonic motion
. This is because when the weight is above the balance point, the spring's tension is reduced so the weight falls due to gravity, and when the weight is below the balance point the spring's tension will pull it back upwards.
If a simple spring system were used in a steadicam, then if the operator moved vertically, the camera would execute simple harmonic motion, and bounce up and down. Instead, an iso-elastic system is employed.
The springs used are large, stiff springs with a high modulus of elasticity, and they are highly tensioned. A compound pulley
system is then used so that the large force exerted by the spring can be divided by a factor of (say) five. The cable exiting the pulley system will have a moderate tension on it, but most importantly, when the cable is drawn in or out, and the extension of the spring changes by only a fifth of that distance, so that the tension force of the spring will not change much. The result is that the spring-pulley system can produce a fairly constant tension in the cable over a large range of movement.
The almost constant force exerted by an iso-elastic system is employed in the armature of a steadicam, to counteract the constant force of gravity on the camera's and mount's mass
. The result is that the weight
of the camera is almost exactly balanced by the tension force throughout the entire range of vertical movement, so even when the operator jumps vertically, the camera will retain its vertical position due to inertia
, but remain balanced, just with the armature at a different angle.
As a result the camera doesn't bounce up to the 'balanced' position after a move, for example when the operator steps up onto a curb from the road. This allows the camera to be more isolated and independent of the operator's moves. The operator can of course deliberately move the camera up or down, if desired.
Elasticity (physics)
In physics, elasticity is the physical property of a material that returns to its original shape after the stress that made it deform or distort is removed. The relative amount of deformation is called the strain....
and tensile
Tension (mechanics)
In physics, tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. It is the opposite of compression. As tension is the magnitude of a force, it is measured in newtons and is always measured parallel to the string on which it applies...
parts (springs and pulleys) which are arranged in a configuration which serves to isolate physical motion at one end from affecting the same motion at the other end.
This type of device must be able to maintain angular direction and load-bearing over a large range of motion.
The most prominent use of an iso-elastic system is in the supporting armature of a Steadicam
Steadicam
A Steadicam is a stabilizing mount for a motion picture camera that mechanically isolates it from the operator's movement, allowing a smooth shot even when moving quickly over an uneven surface...
.
The Steadicam arm is used to isolate a film or video camera from the operator's movements.
Steadicam arms all work in a fashion similar to a spring lamp since each arm has 2 sections (similar to and labelled like a human arm), both the upper and fore-arm sections consist of a parallelogram
Parallelogram
In Euclidean geometry, a parallelogram is a convex quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of equal measure...
with diagonal iso-elastic cable-pulley-spring system. The iso-elastic system is tensioned to counteract the weight of the camera and steadicam
Steadicam
A Steadicam is a stabilizing mount for a motion picture camera that mechanically isolates it from the operator's movement, allowing a smooth shot even when moving quickly over an uneven surface...
sled. This tensioning allows the camera and operator to move vertically and independently of each other. For example as the operator runs, the bouncing of his body is absorbed by the springs, keeping the camera steady. The arm also has unsprung hinge
Hinge
A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components...
s at both ends of each arm allowing it to bend in the horizontal plane (just like your elbow, not like a spring lamp).
To understand how an iso-elastic system works, we must first understand how springs work. The tension
Tension (mechanics)
In physics, tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. It is the opposite of compression. As tension is the magnitude of a force, it is measured in newtons and is always measured parallel to the string on which it applies...
(elastic force) in a spring is proportional to its extension according to Hooke's law
Hooke's law
In mechanics, and physics, Hooke's law of elasticity is an approximation that states that the extension of a spring is in direct proportion with the load applied to it. Many materials obey this law as long as the load does not exceed the material's elastic limit. Materials for which Hooke's law...
. This means that if a weight is hung on a spring it will oscillate with simple harmonic motion
Simple harmonic motion
Simple harmonic motion can serve as a mathematical model of a variety of motions, such as the oscillation of a spring. Additionally, other phenomena can be approximated by simple harmonic motion, including the motion of a simple pendulum and molecular vibration....
. This is because when the weight is above the balance point, the spring's tension is reduced so the weight falls due to gravity, and when the weight is below the balance point the spring's tension will pull it back upwards.
If a simple spring system were used in a steadicam, then if the operator moved vertically, the camera would execute simple harmonic motion, and bounce up and down. Instead, an iso-elastic system is employed.
The springs used are large, stiff springs with a high modulus of elasticity, and they are highly tensioned. A compound pulley
Pulley
A pulley, also called a sheave or a drum, is a mechanism composed of a wheel on an axle or shaft that may have a groove between two flanges around its circumference. A rope, cable, belt, or chain usually runs over the wheel and inside the groove, if present...
system is then used so that the large force exerted by the spring can be divided by a factor of (say) five. The cable exiting the pulley system will have a moderate tension on it, but most importantly, when the cable is drawn in or out, and the extension of the spring changes by only a fifth of that distance, so that the tension force of the spring will not change much. The result is that the spring-pulley system can produce a fairly constant tension in the cable over a large range of movement.
The almost constant force exerted by an iso-elastic system is employed in the armature of a steadicam, to counteract the constant force of gravity on the camera's and mount's mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
. The result is that the weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...
of the camera is almost exactly balanced by the tension force throughout the entire range of vertical movement, so even when the operator jumps vertically, the camera will retain its vertical position due to inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
, but remain balanced, just with the armature at a different angle.
As a result the camera doesn't bounce up to the 'balanced' position after a move, for example when the operator steps up onto a curb from the road. This allows the camera to be more isolated and independent of the operator's moves. The operator can of course deliberately move the camera up or down, if desired.