| I need to add something to my comment. I can't edit it, so here it is. One of the reasons for which a parachute can be considered to be inadequate in terms of failure tolerance for drones comes from the long list of failure modes generated when one goes through the DFMEA process. If, for example, you have a bird strike that takes out one or more propellers (or motors) you could have a situation where the drone is spinning out of control. Don't laugh, I've had this kind of thing happen. In fact, I had a hawk attack and destroy a 2.4 meter drone. Tumbling/spinning can happen for other reasons. One or more motor controllers fail. Software bug. Flight computer failure. Propeller fatigue causing the loss of a blade. Motor/controller overheats. FOD. Etc. Under those conditions a simple parachute deployment design will result in a parachute wrapping around the drone. In other words, it would be useless. OK. We need a more reliable method to deploy the parachute. Maybe we also need three parachutes instead of one. A typical method will shoot the parachute out with some force, perhaps using a strong spring, explosive charge or compressed CO2. The idea being to get the parachute out quickly and as far as possible from anything that could entangle it. You could have a couple of meters of rope before the parachute cords. This would allow for some entanglement without necessarily affecting the parachute. Here's the problem: Now you need layers of safety and failure tolerance for the parachute deployment mechanism. You cannot even consider using a simple mechanism at all. Why? Imagine the simple parachute mechanism launching the parachute at full force in the warehouse, while people are working around it. Depending on scale, you could seriously hurt or even kill someone. And this is how we descend down a road that can make failure tolerance very expensive. As I said, this can be very hard to justify in commercial products. Simple example of a design we completed a couple of decades ago. A failure-tolerant coolant recirculation pump. I won't get into the entire design. We had to have a custom motor made that effectively consisted of two motors built on the same shaft. You could not simply use couplers to link to single motors together because then the coupler becomes a single point of failure element. A solid shaft was deemed to be the most secure option, hence the custom motor. These kinds of decisions are not cheap. Particularly when you are making less than, say, 10K units. |