I don't believe there is any simple way to load an ESC with a passive load since the ESC relies on the back EMF from the rotating motor to synchronise the drive pulses.
You can however use a motor driving another motor with shorted windings (ie as a generator) as the load. It's no longer simple, and approaching a true dynamometer test.
Simpler to use a direct passive load on the battery. This can be plain resistive, like light globes or power resistors, or active such as a controlled voltage regulator into a resistive load or a controlled FET Load. If you want a known constant current or power load then it has to be actively controlled.
Originally Posted by chuck75
I cannot help but wonder if there is a way to modify an ESC to work with 3 passive loads to simulate high power conditions that occur in flight. Or, I suppose that a motor with a load other than a flight propeller might be used as a load.