DC Motors have a limited amount of power that they can output, which means that for a specific amount of work (i.e. lifting a weight over a set distance), the motor can only do it so fast. To ensure the motor will spin at a reasonable speed and draw a reasonable amount of current, the motor load must be below a certain threshold. The motors in their default configuration are too fast for a typical applied load – they are trying to accomplish the work faster than their power limit will allow. So if the motor must lift a certain weight while still staying under the design threshold, mechanical advantage must be used.
This unit will show how gear ratios can be used to adjust mechanical advantage so that the motors can do the work more slowly, within their power limit.