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| Load
Handling |
Probably the
most common question asked by many customers is: how much weight can
it handle? While this question may at first appear quite simple, the
answer is actually more complex than most may initially realize. Loading
conditions are determined by many factors including: horizontal or vertical
orientation, rotational velocity, mass of load, the acceleration function
used, distance from rotational center, and perhaps resistance or torque
loads of external customer rigging or structures.
To illustrate the complex dynamics of this mix of variables, one could say
that a well setup and balanced 1000lb load could be more easily driven than
a poorly setup 100lb load. Therefore the load handling capabilities are
very much a function of how well the user constructs, mounts, and supports
the loads with the LT360EX. |
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Thrust & Radial Static Loading
The drive assembly of the LT360EX is robust and consists of
two heavy aluminum castings mounted between a 125mm (5 Inch) ball
bearing. The axial static thrust load rating for the bearing is 8000
lbs (4000kg). The thrust load rating is bidirectional, and can be
either pulling or pushing. Radial or side loading of bearings is always
much less, probably on the order of several hundred pounds.
The load capability for the two castings depends greatly on how evenly
the load is attached to the castings. If the load is bolted properly
and rigidly to the surfaces, with the weight concentrated in the center
region, the castings should easily handle 1000 lbs or more.
If the load is not attached to the platter and base properly, than
the castings could fracture with smaller load stress. Therefore it
is critically important that any jigs being mounted to the platter
and base provide their own rigid surface strength to avoid excess
stress at the outside edges of the castings. The LT360EX chassis
should never be used as a primary support structure for load
handling. All loading should be applied to the castings with the provided
mounting points. |
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Horizontal Torque Loading
The case of horizontal torque is shown in the pictorial here. This
is probably the most common configuration for setup. In this case
the LT360EX is located on a horizontal surface, or on a ceiling,
and the load is rotated in a horizontal plane with no change in the
vertical axis. |
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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)
Since there is no change in vertical position, gravity is not a factor.
The only acceleration acting on the load is due to the LT360EX.
For the LT360EX model the maximum platter driving torque is 100NM
(Newton•Meters). We will assume that the rotational velocity is
set to 1 RPM, and that the Flat acceleration function is in use.
With these operating conditions the average acceleration for the Flat
acceleration function is about 0.21M/S2 at 1 RPM and 1M. Therefore the
maximum mass load which can be rotated is:
LT360EX, 1Meter, 1RPM, Flat Accel Profile
M=T/(R•A) = 100/(1.0•0.21) = 476kg = 1047 lbs
The mass load capability for other operating conditions can also be calculated
as easily. Reducing the centroid load distance by half will double the
mass load capability. It should be noted that the acceleration is proportional
to the square of RPM. Reducing the RPM by a factor of 2, reduces the acceleration
by a factor of 4. The greatest load handling ability with chopper current
drive is provided for RPM values less than about 2 RPM. At higher RPM
velocities the torque is greatly reduced. This is due to the inductance
of the motor limiting the current. High velocities such as the maximum
12 RPM will only be suitable for driving minimal light torque loads. |
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