Calculating 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.

OHL= Tout R Example: 10 in-lbs output torque 0.5 in. radius sprocket OHL= 10 0.5 = 20lbs Overhung Load Calculator Load Device Sprocket Gear Pulley Output Torque (in-lbs) Radius (in) OHL Value (lbs)

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.