Power is the bane of drone pilots. You’d like to fly longer which means a bigger battery. But a bigger battery will weigh more which leads to less flight time. You have to strike a balance and for most consumer drones that balance is about 20 minutes of flight time, more or less. Researchers at Berkeley have a different idea: don’t use a bigger battery, but simply replace the battery in flight.
The idea isn’t completely new. After all, many planes refuel in flight — a technically sophisticated operation, but it occurs every day. The scheme here is to have a primary battery and a secondary battery. When the secondary battery is low, the drone ejects it while running on the primary battery. Another secondary battery flies to the drone and docks with it becoming the new main power source.
In theory, it sounds pretty simple. In practice, though, you really have two drones. The main drone and a smaller one that carries the battery back and forth. Of course, you also need a way for the drones to find each other and dock.
The devil is in the details. Do you put a separate battery on the flying battery or do you let it sip from the payload’s charge? Do you fly batteries away gracefully or just dump them? How do they find each other? All things for a designer to consider. You also don’t want to put two wildly mismatched batteries in parallel, so the design uses some diodes, a FET, and a relay to keep the power source to one battery at a time.