The 3DR drone was used because it is an extremely durable drone, therefore it can handle being roughed around and crashing several times. It can also be programmed using ArduPilot open source software (e.g. Mission Planner).
A downside to the durability of the drone, is that it is quite heavy. When flying the stock drone around, there was some lag which made it tricky to control and increased the learning curve.
To solve this, we took the drone apart and made some modifications.
The drone body needed weight reductions. A 1 inch hole saw was used to drill holes into the side of the body. These holes were carefully planned out to keep them relatively equally spaced. This got rid of excess material without compromising the structural integrity of the drone.
The plastic bottom of the drone was deemed unnecessary as well. This was cut out using a handsaw at first, which was quite difficult so we ended up using a Dremel tool instead.
Later on, we would end up attaching a metal plate to the bottom for increased structural integrity.