Most configurations such as quadcopters, don't offer any intrinsic redundancy (in spite of having 4 motors). The failure of a single motor will prevent the quadcopter of maintaining level and yaw-locked flight. Some enhanced control algorithms are being developed to provide level and controlled descent in case of single motor failure. Naturally, yaw control is lost, but the on-board inertial sensors and magnetometer are capable of keeping track of the orientation, therefore knowing how to distribute throttle by the surviving motors.
My current goal is to make, and go through the challenges of creating a parachute device that can be deployed in the quadcopter in case of loss of power or freefall.
Right now, I have the physical parachute, that I have built a few months ago, but never had the chance of testing.
As such the first test that I have defined is to carry the parachute on the underbelly of the quadcopter, and hold it through a release mechanism. Even though is well below the expected payload, I have added a cilinder filled with AA batteries, in order to fulfill 250 grams of weight:
The release mechanism is basically a 9 gram servo attached to a plate having a slit through which the edge of rubberband that holds the parachute, is held. A link bar connected to the servo holds the edge of the rubber band. Once the servo is moved, the link bar is moved outside of the slit, and the rubberband is free, therefore releasing the parachute:
The first test can be found here:
The release mechanism worked flawlessly in the two tests that were performed. In the first test the parachute didn't open at all, but also the limited altitude of 8 meters at which the quadcopter was hovering did not allow the necessary airspeed to build up.
In the second test the parachute was dropped higher, and there are already signs of the parachute starting to open.
Finally some canopy inflation tests :)
ExperimentalAirlines - https://www.youtube.com/channel/UClkL_Hmktyh9R_FzwSPjXmA