Motorized Pan Tilt Heads, What is torque?

It is easier for you to hold a weight near your body. Less torque.It is harder for you to hold a weight extended out from your body. Greater torque.

It is easy to feel the difference.

This is much harder for the motor to hold, and harder to tilt the weight upward. Notice the weight is extended from the camera mounting plate. The weight with the target represents your camera. The center of gravity is the center of the target painted on the weight.

This is easy for the motor to hold,
and easy for the motor to tilt the weight upward. Notice the weight is close to the camera mounting plate. The weight with the target represents your camera. The center of gravity is the center of the target painted on the weight.

It is easier for you to
hold a weight near your body.
1 ft x 5 pounds = 5 ft-lbs
Low torque.

It is harder for you to hold a weight extended out from your body.
3 ft x 5 pounds = 15 ft-lbs
3 times more torque.

This is much harder for the motor to hold, and harder to tilt the weight upward. Notice the weight is extended from the camera mounting plate. The weight with the target represents your camera. The center of gravity is the center of the target painted on the weight.

What is torque?
A force, which tends to produce rotation.
The measurement of torque is based on the fundamental law of the lever.
It is the power needed to twist an arm with a load.
It is measured by multiplying the distance by the weight (foot-pounds).
Torque Formula L (length) x F (force) = T (torque) -or- L x F = T
Example: A 2 foot lever with 200 pounds at the end will produce 400 foot/pounds of torque. http://en.wikipedia.org/wiki/Lever
http://en.wikipedia.org/wiki/Torque

Example

How does torque relate to motor power?
The heaver the load the greater the power needed to move the load.
The further the load is from the rotating axis the more power needed to move the load.
http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm

Is a pound rating all I need to know?
No, the pound rating is a simple way to express the motor strength, but torque is more accurate.
http://www.scienceprog.com/easy-way-to-measure-motor-torque/

What does foot-pounds mean?
Foot-pounds is a torque rating. It is equal to the arm distance times the weight that is being lifted.
With a human arm (see above image) it is measured in feet from your arm pit to the center of the chrome weight
and the "pounds" is the weight of the chrome barbell.
With a pan tilt unit the distance is the measure from the axial to the center of gravity of your camera,
the weight is the camera weight including the lens battery cables etc.
The motor strength needed for lifting or tilting is the number of feet times the number of pounds.

All three images have a line drawn through the tilt axis. This is the point where the measurement is started.
The "center of gravity"* of your camera is the point at the other end of your measurement. This measurement gives you the "foot" part of the foot-pounds for your torque rating.

The "pounds" part is the weight of your camera, lens, weatherproof housing, cable draping down, etc.

This image has a line drawn through the tilt axis

*The center of gravity (or center of mass) of your camera may not be the center of your camera, see;
http://en.wikipedia.org/wiki/Center_of_gravity
In the images above the center of gravity is the center of the target painted on the weight.


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