Definitions and Principles of Inertial
Some types of inertial stabilization:
MECHANICAL INERTIAL STABILIZATION:
Stabilizing a camera in space using the basic principles of inertia. Steadicam,
Tyler Mount, Body Cam, Pogo Cam, Glide Cam, Handy Man, Doggie Cam
BRUTE FORCE GYROSCOPIC INERTIAL STABILIZATION:
(Kenyon and Tyler Gyro mounts) Kenyons are being added to many inertial devices
with excellent success.
FEEDBACK INERTIAL CAMERA STABILIZATION:
Using inertial camera position information to compensate for unwanted movement
from the camera support. (Westcam, Gyrosphere,)
FEEDBACK INERTIAL IMAGE STABILIZATION:
Using inertial camera position information to compensate for unwanted camera
movement by shifting the position of an optical plate within or in front of
the lens. (Dynalens, Arri Image Stabilizer, Canon 2/3" Stabilized Video Lenses,
and better Mini-DV camcorders.)
FEEDBACK INERTIAL VIDEO CHIP IMAGE
STABILIZATION: Using inertial camera position information to shift the image
around on an oversize video chip. Used in cheaper consumer video camcorders
This is mostly a discussion of MECHANICAL
THE BASIC ELEMENTS OF A MECHANICAL
INERTIAL STABILIZATION (Dexter's definitions)
THE CAMERA SYSTEM is connected by
the CONNECTION SYSTEM (CS) to the ISOLATION SYSTEM (IS) which is attached to
the SUPPORT SYSTEM (SS). I suggest that you print out "Heavy Camera Horizontal
Rig", "Low POV Rig", "Industry Standard Examples", and "Handheld Vertical TEE
Rig for Camcorders" and refer to them as you read this discussion. You might
skip by sections that are not clear and return to them later. You might also
down load and study some of the US patents as referenced.
1. THE CAMERA SYSTEM is a group of
camera and counterweight elements rigidly connected and balanced around a CENTER
OF GRAVITY (CG). The camera system elements MUST include the camera and 2 separated
counterweights (CW). These counterweights CAN include extended film magazines,
extended motors, batteries, video assist, viewfinders, video transmitters, one
or more Kenyon Gyros or simple inert counterweights if not one of the above
a. There must be 3 separated weights
to stabilize a camera system in all 3 axes. More than 3 weights DO NOT add stability
and makes a system more difficult to balance about the camera system's CG. (Consider
a long camera or sled as two separate weights.)
b. The camera system components should
be rigidly connected so that the system can't flex under stress from support
system (SS) movement.
c. Weight farther from the CG makes
the system the more stable. The farther a weight is from the CG, the lighter
it can be for the same effect. Limits for size are clearances such as going
through doorways and the operator's body. It is possible to make a device that
is so large that it is so stable that the operator cannot easily control it.
d. Weight near the CG reduces inertial
stability, but if the camera is close to the CG, lighter weights attached at
a distance reduces the total camera system weight. (See Beta Cam/Arri BL Rig)
e. Adjustments to balance the camera
and/or counter weights about the CG should be easy to make. Lightweight dovetails
are ideal for camera. Adjustments should have stops so a camera or counterweight
can't slide off while adjusting. A zoom lens should be securely attached. (See
Center of Gravity Test Rig)
f. To find the CG of a camera or
non-symmetrical counter weight component, balance it on a round pencil on 3
g. Film moving in a magazine can
be compensated for by a movable weight that can be adjusted between shots. This
weight should move in line with the spindles of the magazine to compensate for
the weight of film moving. .
2. THE SUPPORT SYSTEM (SS) consists
of a means to support the weight of the camera and isolation systems (IS) and
is attached to a vehicle or an operator's body. The simplest support is the
human body, but the average human arm is limited to about 8-lb. total camera
system weight held away from the body. (Steadicam Jr. ©. Steadicam Jr.
DV ©, Pogo Cam) Heavier weights can be held comfortably closer to the body,
but heavier camera systems usually need more sophisticated support systems than
the human arm.
a. The support system (SS) [Steadicam © Vest or Body Cam © Backpack] should be securely attached to the
operator so that there is no movement between the two. A vehicle SS should be
securely attached to its vehicle.
b. A means should be provided to "park" the camera system for loading, resting the operator and balancing the
system when removed from the isolation system.
3. The CONNECTION SYSTEM (CS) allows
the camera system to move freely without unwanted torques from the support system
being transmitted to the camera system. The connection system is attached at
or near the CG of the camera system. [Gimbal]
a. The simplest connection between
the camera system and the support system is the human hand. This works well
for some medium weight hand supported devices with extended weights. [Pogo Cam]
Light weigh systems like Steadicam Jr. © need more complicated isolation.
b. Except for hand gripped devices
like Pogo Cam, friction must be minimal at the connection system between the
camera and isolation systems (IS). Bearings allow the camera system to remain
stable and not be influenced by support system movements. A fiber cord from
an above support attached to the camera system's CG works too. (Patented in
Germany in 1927 # 441148) A vertical spike from below resting in a cone in the
camera system at its CG is also very simple and works well. (Patented in the
1936's for the Eymo Camera US Patent #2,036,097)
c. If the camera system is attached
to the isolation system (IS) slightly above the CG of the camera system, gravity
will help keep the camera's horizon level. [Ala Steadicam © US Pat. #4,017,168]
The operator must make slight corrections when starting or stopping a move.
d. If the IS is made of bearings,
they must be in the same plane. If a pan bearing is not level with the tilt
bearings, the unit will fall to one side on its own.
4. The ISOLATION SYSTEM (IS) absorbs
the relative motion between the support system and the camera system. This can
be a combination of arms, cables, levers and springs. [Steadicam © and
Body Cam ©].
a. Steadicam © type systems
use a spring and lever arm to support the camera system weight and isolate the
operator's walking movements from the camera system.
b. Back pack mounted systems such
as the Body Cam © /Body Mount support the camera from over the shoulder
with less strain on the torso at the expense of limited overhead and side to
side clearances. (US Pat. #4,206,983)
The above two devices each have their
advantages and disadvantages. Practice with any device helps overcome disadvantages
and develop appropriate the operator's skills.
c. Helicopter mount systems like
Nelson Tyler's use massive weights and balance every movable element about its
CG to isolate the camera from the helicopter's movements. The vertical post
allows the upper camera section to remain stable in space as the helicopter
body oscillates around the camera system. (A very simplified explanation of
a complex system.) (US Pats. #3,352,521 and #3,457,350)
d. Various camera system designs
can be hung from above with springs or bunji cord to isolate the camera system
from undesired movement of the support. Those and spike from below systems will
be discussed in this site.
5. GUIDANCE SYSTEM (GS). The camera
should be guided close to the CG or symmetrically extended from the camera system
CG as in the Tyler Helicopter Mount and Body Cam ©. If the camera system
is controlled by a force any distance from the CG or not symmetrically in line
with it, the camera system will be pushed unequally out of balance when the
operator tries to control the camera.
The smaller the guidance point is
in relation to the size and weight of the camera system, the less likely the
operator is to over correct intentional moves. I have found a 3/8" diameter
Allen head screw head (of a 1/4" Allen screw) guided by finger tips ideal for
a 4-6 pound human arm supported device. This screw head is also the cone socket
where the camera system is supported from below by a spike sticking up in a
handgrip. A whole hand wrapped around the post of the much heavier Steadicam
© is right for the weight of the Steadicam © camera, post and sled.
6. OTHER FACTORS AND SOLUTIONS
Counter-weights should always be
working parts of the camera system if possible; batteries, monitors, extended
film magazines, motors, extended motors, video transmitters, focus systems etc.
The camera and/or counter-weights must be adjustable about the CG to allow for
balancing the system. Balancing adjustments at camera or the heaviest element
is the most sensitive. If batteries and transmitters are not convenient as part
of the camera system, they can be carried on the operator's body and connected
by cable. Flexible lightweight power, video and control cables should be attached
close to the camera system CG to prevent unwanted torques effecting the camera
Adjusting the camera system's CG
to the attachment point must be easy to do. It helps to keep every component
symmetrical in one plane with the CG and connection system. If you use tube
(or pipe), balance every part about the tube’s center. Modified Speed Rail ©
"Tees" (#5) will do for T shaped devices. Cut a coupler (#70) in two and weld
a half to the side outlet of a tee (#5) to give it enough strength. Speed Rail
© crosses (# 10 or 30A) join the two pipes out of line in a plane and create
an imbalance that is hard to correct. Vibration Dampening Clamps are also useful
and come in most pipe and tubing sizes. Make sure adjustments cannot slip under
Front to back and side to side horizontal
adjustments are easier to make under load than vertical up and down adjustments.
Up and down adjustments can be made easier if the camera is pointed up or down.
(If design allows, such as horizontal TEE rig.) Make each horizontal and vertical
adjustment independent. Make sure that no camera parts can fall off when adjusting
the CG. Consider small movable weights to fine tune larger masses.
The isolation support arms or devices
should be as light and flexible as possible. The weight of an isolation system,
such as a heavy mechanical arm effectively adds weight to the camera system
at the CG of the camera system and reduces inertial stability. A vertical fly
fishing rod bent 180 degrees is the simplest and best example of an ideal support
and isolation system. It is flexible in all directions has almost no mass, but
unfortunately will only support a couple of pounds.
A bunji cord from a high support
is also a simple and very light weight isolation system. It could support a
very heavy camera system from a high ceiling of a sound stage or crane. The
higher the anchor point, the more flexibility the operator has. Primitive, effective
but will not impress the on-lookers even it the film looks great. Expect howls
ERGONOMICS: Any device should be
as operator friendly and interface with the human body as much as possible.
Designs should take into consideration clearances of the operator's limbs and
the most comfortable operator positions for the camera system. Controls and
viewfinder position should be ergonomic. The Tyler Helicopter Mount and Steadicam © are excellent examples.
WIND RESISTANCE AND FRICTION.
If a device is involved with wind resistance moving at higher speeds such as
on a vehicle, consider balancing surface areas to the wind around the CG and
/or support point. Large matte boxes and magazines can be a problem. Use an
effects fan to test for aerodynamic balance.
TETANUS: While the human body/brain
is a million dollar support and guidance system, the human arm will support
only a certain amount of weight before muscles start to fight one another (tetanus)
and add instability. The average non-athlete can hold only about 6 to 8 pounds
out from the body with one hand and not become unstable. Practice and exercise
helps increase this weight limit. Tetanus also increases with general fatigue.
The motions of the operator must
be isolated from the camera system as much as possible. A hand firmly gripping
a lightweight (4lb. to 8lb.) camera system at a support point can transmit the
operator's body movements to the camera system.
The operator's eye should be isolated
from the light to medium weight device eyepieces so that the operator's head
movements are not transmitted to the camera. This is little problem with helicopter
mounts because they are so heavy that a little pressure from the eye doesn't
effect the camera system.
So the ideal device has its weights
concentrated at its extremities. Every weight is a working part. The camera
system's connecting members weigh little but are very rigid. The camera system
is well isolated from the support system. The control point is at the CG or
symmetrical with it. And the whole thing is ergonomic and easy to adjust balance
about the CG.
VIEWFINDERS: Moving hand held camera
shots require less exact framing than a tripod, crane or dolly mounted camera
shot. The simplest and most reliable viewfinder for an eye level camera is a
wire frame. Video is standard with most systems. Some CRT helmet view finders
gives a good image in bright light but must be gotten used to. Some LCD finders
may still be too dim in bright light and need a neutral density mask to reduce
outside light to the eyes to balance the brightness of the LCD image. Emission
from a CRT close to the eye and brain is a health concern.
VIDEO HELMET DESIGN CONSIDERATIONS
1. The operator should have peripheral
binocular vision below the viewing image so he can maneuver his body safely.
2. The helmet should be as light
as possible and fitted firmly to the head. The weight of the monitor should
be balanced on the other side of the head if possible. This can be done with
3. The image should appear at or
near infinity to allow the operator to shift attention without eye accommodation
(distance focus) from his environment viewed directly below the viewfinder image
and to the image in the video monitor.
4. The monitor should be viewable
in any light.
5. The system should be as compact
THE PROBLEM WITH HELMET FINDERS:
Most people find it impossible to look at two different images at the same time.
Some get sick immediately. A good way to avoid this is to practice shooting
with both eyes open when operating any camera and shifting attention from one
eye to the other. One eyelid can blink closed. While shooting with a regular
camera you can watch for things happening out of the frame seen in the viewfinder.
This takes practice, but is an invaluable skill. Using the helmet finder then
becomes much easier.
APPLICATIONS OF INERTIAL STABILIZATION
TO CAMERA CAR AND MOVING CAMERA SITUATIONS
Balancing the camera weight about
the pivot points of the tripod or remote head increases stability. (See Prof.
Rigging / Inertial Tripod Head)
Keeping the operator's eye away from
the eyepiece is important to reduce motion from the operator's body.
Operator's comfort is important to
allow him to concentrate on framing, focus, performance and judging camera stability.
The ability to pan and tilt to extreme
angles easily should be considered. Although the video tap images are less desirable
than looking at the ground glass, they are worth trying. A parallax color video
camera gives a better image to see detail than a video assist of the ground
A study of the movements of each
support vehicle is important. Each has different motion. A helicopter has an
oscillating rotary motion as the body of the chopper vibrates below the supporting
blades. Balancing the blades is very important. An airplane is very susceptible
to disturbances in the air. It gives a tilt and horizon level disturbances if
shooting to the side. Both have engine vibration to remove. Dollies and land
vehicles have road and track bumps to contend with that tilt the camera if not
inertially mounted. These can be reduced by an inertial head and strong support
to the vehicle frame or close to the wheels if the body flexes.
The human body walks with a front
to back and up and down gate that has to be isolated. The camera and support
system makes smooth walking harder. Fatigue and damage to the body are very
© Copyright 1999-2004 Ron Dexter. All Rights Reserved.