My kids have been tearing apart a number of different gadgets, from RC cars, to toys, to coffee makers.
There are a variety of cool little motors and lights in these devices that we would like to use on oddball projects. (For serious projects, I prefer to spec out the component and purchase it directly)
So far, I've been using a variable voltage DC power supply to guess the right voltage based on what seems to be the correct speed, brightness, etc... without burning the item out.
Is there any scientific or mathematical technique that can be used to know when you are at a correct level of current or voltage for a given device, or does it simply depend on the specifications of the device?