A drive unit has an output subject to changing loads, where the drive unit consists of fixed and moving parts connected to a power source. The output of the drive unit is controlled in cycles, and for ascertaining the load in a given cycle, the time period required for changing the position of the moving part of the drive unit, or for changing the position of the moving part of the equipment in mechanical contact with the moving part of the drive unit, from one predefined position to another predefined position is measured, whereby the input required in the next cycle is determined according to the time period ascertained in at least one preceding cycle. Where the drive unit is an electric motor, the input required in given cycle is also determined according to electric resistance of the electric motor ascertained in at least one preceding cycle.