How we safely put the "variable" in "variable-speed hoists"

A blender is a fine example of a variable-speed machine.  Between mix, whip, puree, and frappe, a number of buttons will make your blender spin at a variety of different speeds. It does this by adjusting the amount of power delivered to the motor.  Less power means a slower speed and - most notably - less torque to spin the blades.

When it comes to hoists, we never want to lose torque - this could cause a heavy load to overcome the motor and begin to fall. To prevent this, we take advantage of vector drives.  Not to be confused with other types of VFDs (variable frequency drives), our vector drives apply full power to the motor at all times during operation. This means that even at zero speed, the motor has full torque to hold and move that heavy load.

How can a motor have full power and also be at zero speed, you say?

A vector drive utilizes another property of AC power - frequency. Remember "AC" means alternating current and standard wall voltage/power in the US operates at 60Hz. This means that 60 times per second, the motor windings get a "signal" to move. A vector drive alters this frequency to change how often the motor windings receive that "signal" to move. Thus when the vector drive outputs the full voltage at 30Hz, the hoist will move at half speed. To stop the hoist (using the motor alone), the vector drive will output the full voltage at 0Hz.  With this kind of control, hoists can move at zero speed, full speed, or anywhere in between without worries of losing torque or dropping that heavy load!