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Overhung Load
Overhung load is defined as the radial
load on the ouput shaft extension produced by a pulley, chain
sprocket, gear, crank arm, cam or other similar device.
The overhung load can be determined by dividing the output torque
by the radius of the sprocket or pulley.
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OHL
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OHL= |
| Tout |
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| R |
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Example:
10 in-lbs output torque
0.5 in. radius sprocket
| OHL= |
| 10 |
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| 0.5 |
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= 20lbs |
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The basic overhung
load must then be modified as follows:
For chain sprockets, the basic overhung load can be used because
there is usually no initial tension in a chain drive.
The typical gear produces a tangential force and a separating
force. Therefore, the basic overhung load must be multiplied a
a factor of 1.2 to allow for the resolution of these forces.
A flat or V-belt drive employs considerable initial tension in
the belt. This initial tension allows the belt to properly transmit
the load without slipping. However, it must be taken into account
in the overhung load calculation by multiplying the result of
the basic OHL formula by a factor of 1.5 to 2.0.
When the calculated OHL value
exceeds the rated OHL value for the gearmotor, the application
must provide a means of isolating the load via a separate load
shaft and coupling with appropriate supporting hardware. An alternate
method is to mount the load device directly to the gearmotor,
but support the gearmotor via the output shaft and not the gearmotor
case.
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