Thoughts on Charging

Maximizing the utility of any electric vehicle means careful consideration for the charge and discharge the battery will experience under normal operation.

An electric weed wacker might see a dozen uses a month, whereas the drones I’m currently designing need to see roughly 150 cycles per month to generate the minimum profit necessary to justify their placement at that particular retailer or vendor. 

One way to mitigate this load is to introduce battery swapping, which could allow you to increase the battery:drone ratio to 2:1 and therefor halving the average usage. In V7.2, the one currently on this site, the battery units weigh 9.7 lbs (4.4 kg) each. This was my solution to the bulky battery problem; one 19.4 lbs battery is cumbersome, but two 9.7 lbs batteries are easy to balance with two hands, like buckets of water. The next drone version, V7.3 reduced the battery mass by 33%, and V8, which I’m outlining currently, will maintain this reduction. My hope is to design a battery unit anyone can easily transport and recharge at a station (CAD screenshots coming). This will allow me to stress test the battery and determine that critical ratio of batteries to drones I mentioned. 

The charging station has existed on paper for a long time, but now I’ve decided to make the first design, which I’ll Introduce alongside the V8 drone to create a more complete vision of how this design will interact in a retail and vendor environment. The needs of the recharging station that I’ve outlined so far are fairly basic and straightforward:

  1. Meant for stationary operation, but not impossible to move.
  2. One size, meant for keeping two drones in constant operation.
  3. Meant for indoor operation in a climate controlled environment, but designed for safe and reliable operation up to ~100 Degrees Fahrenheit (38 C).
  4. IP22 rated, a common minimum safety rating for indoor use, which provides regulatory assurance that fingers wont get pinched or zapped and that the device won’t become unsafe if overhead sprinklers drench it. 
  5. LED indicators (no gaudy LCD screens) for reasons of reliability, visibility, and simplicity. 
  6. USB interface for diagnostics.
  7. A standard internal current limiting circuit.  
  8. A phone/tablet rest.

So with two battery units per drone, a good number of charging slots per unit might be 8, which would allow 2 drones to be discharging 4 batteries (40 min flight time + 10 min loading/unloading) for a total of 50 minutes. 

While 50 minutes isn’t enough to get a decent charge on a large LiPo, 100 minutes can get you anywhere between an 80%-100% charge depending on the charger / battery combo. This is on justification for the extra staged slots. While 4 batteries are in the air, 8 more are charging in the desk unit. So when both drones complete their 50 minute circuit, the 4 batteries that have been on charge the longest are up to bat. The 4 expended batteries from the drone take their empty slot.  

This is another reason flight time is so important to the overall drone delivery experience; not only does it enable more miles traveled, but it also enables a series fo short deliveries in a metropolis to be carried out in quick succession without need of a battery swap.

If this sounds futuristically absurd, consider that a vendor in a city might only be 2.1 miles away from a customer. Currently, road-based delivery services inevitably waste time in traffic and at stoplights (even if made autonomous). A 2.1 mile trip might feature 15 major intersections, each with a ¼-⅓ probability of introducing a 30s-120s stop. A capable drone could complete several such trips in succession, all while consuming less energy from the grid than an electric car, and in fact eliminating that hypothetical car from the roadway to begin with. 

A drone properly designed around a deep cycle battery means the user isn’t required to swap batteries every time a landing and reload occurs. And when a battery swap is needed, even in the heat of rush hour, the Recharge Unit will be designed so that its maximum rate of comfortable recharge exceeds the maximum discharge rate of the drones at that particular network node. 

The Recharge Unit will be critical for a pleasant and efficient user experience. I have designs, but don’t want to devote time to an image capture until the V8 drone is ready to be introduced alongside the Recharge Unit.