This footage is from an x8 drone I built winter quarter of 2024. x8 refers to the fact that there are four pairs of counter-rotating props, for a total of eight. This 8.8 lbs drone produces around 20 lbs of thrust, has a maximum flight time of 20 minutes, and a range of over 4 miles.
In order to achieve better flight times and to reduce cost this drone has a custom-built lithium-ion battery pack. It is a 4s6p battery made from 24 spot-welded 21700 cells for a total of 24,000 mAh of capacity. The challenge with drone batteries is amp output, at maximum power the eight electronic speed controllers can output 400 amps of current, as much as a medium-sized car draws on startup. To provide this much amperage, without experiencing voltage sag, specialized high amperage 21700 cells are needed. The connections between parallel groups also need to be capable of handling high amperage.
The toughest part of this project was the custom frame. With only a few hours of Solidworks experience going in, the learning curve was steep. After many long hours, revisions, and reviews I had a design I was happy with. The rods that make up the frame are 1 cm diameter carbon fiber tubes. These are connected with 3d printed joints at each intersection. Some of the joints are then wrapped in a carbon fiber wet layup for further reinforcement.
