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Vertical Torque Loading
The case of vertical torque is shown in the pictorial here. In this
case the LT360EX is located vertically relative to the ground
surface. In this configuration the mass load is being acted upon
by the acceleration of gravity. The acceleration of gravity is 9.8M/S2,
generally much larger than the rotational acceleration of the LT360EX.
For this reason the mass load capability will be greatly reduced.
The torque load is equal to the product of radial distance and force,
where force is is the product of mass and acceleration.
F = M•A T = R•F = R•M•A M=T/(R•A) |
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Since the
vertical position is changing, gravity is a factor. Depending on the position
of the load, or the rotational direction, the acceleration due to gravity
will add or subtract from the rotational acceleration of the LT360EX.
Based on typical operating parameters of 1 RPM, 1 Meter, and a Flat acceleration
function, the acceleration is about 0.21M/S2. However the acceleration due
to gravity is 9.8M/S2 about 50X larger. The actual acceleration due to gravity
changes around the circle from zero at the bottom or top, to the maximum
at the sides. Since the rotational acceleration is so much smaller than
the effects of gravity, we will simply assume the worst case acceleration
as equal to gravity. Therefore the maximum mass load which can be rotated
is:
LT360EX (100NM), 1Meter
M=T/(R•A) = 100/(1.0•9.8) = 10.2kg = 22 lbs
Note that the mass load capability in the vertical configuration is not
a function of the RPM or acceleration functions of the LT360EX. Gravity
dominates the acceleration entirely. Larger mass loads can be handled by
reducing the radial distance. Reducing the distance by half will double
the mass load capability. This configuration is not very useful for load
rotation due to the limits of gravity. It is comonly used to rotate a lighter
weight boom and microphone for this axis.
From these calculations it should be clear that the centroid of the mass
load must be fairly lightweight or located fairly close to the rotational
center, to avoid creating large torque requirements. In the vertical configuration
acceleration due to gravity is the limiting factor. |
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| Acoustical
Noise |
In most
applications where acoustic measurements are to be performed, the
LT360EX will be used to rotate the device under test to a specific
position, and then the measurement taken while stopped. In this application
the LT360EX is not rotating while the measurement is in progress,
and noise is not a factor. The LT360EX produces virtually no
noise when it is not rotating.
However in some acoustic measurement applications it may be necessary
or desireable to perform measurements while the device is being rotated.
In this situation noise from the LT360EX may or may not be
an issue. |
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Noise is
generated by the stepper motor and drive assembly when the LT360EX
is actively rotating the load. The 1/3 octave noise spectrum is given
in the graph above. The broad spectrum noise is:
50dBspl @ 2M, 1 RPM, ANSI-A Weighted
It should also be noted that a mounting structure and/or rigging can also
produce noise when in motion. This can arise from many sources including:
bearing or wheel squeaks, joint interface squeaking, etc. To minimize
all noise sources bearings should be well lubricated and bolted joints
may need special treatment of rubber pads or similar between the members.
The self noise of the LT360EX itself can be reduced by using an
isolation box surrounding it or similar means. |
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