Miniquads and Safety – Rational Analysis Attempt

Miniquad safety is a murky subject. At first glance it seems obvious that a miniquad is a potential dangerous object, perhaps even lethal. A quadcopter traveling in a straight line at the height of  a person’s head has the potential to seriously hurt or kill somebody. There is a fair amount of offline discussion around this topic, but unfortunately most of it is based on speculation and feelings as opposed to reason and hard numbers. This post is an attempt to do the latter.

It’s important to acknowledge that all of us partake in activities that are dangerous to others. Some are arguably necessary; if you have to drive to work, you are a statistical contributor to the roughly forty thousand road deaths that happen in the US on a given year. But what about the unnecessary driving all of us do? From a statistical perspective, going on a recreational 1000-mile road trip has 1/100,000 odds of resulting in one death. This is very significant, because a large amount of driving in the US is of this type. Recreational driving kills at least hundreds of people each year. Nobody is on a crusade against unnecessary driving, just because we are not robots that think about the public good. We are imperfect, selfish, and get emotional about things that are often not the ones that matter most.

I imagine some people may be put off by the comparison with driving. Driving is accepted and part of our culture, like alcohol and guns. Miniquads are not. They are new and scary. Because they are a recent development, there is not enough data to write a paragraph like the above. How many people die per million miniquad flights? We do not know. The close we could get to this number would be by estimating the number of batteries flown every day, and finding records of all people killed by miniquads. I personally have not found any records of deaths caused by miniquads, but that does not mean they have not happened (I would honestly welcome that information).

It is possible that a miniquad is not as dangerous as some people believe. Let’s consider all the things that need to go wrong for someone to be killed by a miniquad. Here is an example scenario:

Miniquad near road

An operator is flying a miniquad near a road, trying to keep some distance (let’s say no closer than 20 feet). If the operator has no intention of going over the road, some type of failure must occur. The most common failures with fpv miniquads are:

  • power train failure (motor, esc)
  • loss of video
  • loss of control

In the first case, most likely the miniquad will drop. Unless it was traveling relatively fast and in the direction of the road, it is very unlikely that it will land on it. In the second case, the operator has the responsibility to deactivate the miniquad right away (or set it into a mode that would stabilize it and climb out of danger). Video loss should not cause the miniquad to hit a road unless the operator makes a mistake.

Loss of control is the most likely reason the miniquad could impact the road. This is largely preventable. Again we do not have data to back this up, but empirically most control losses in radio control are due to various operator mistakes such as flying out of range or having damaged antennas. Interference is also possible, but this mostly happens when several miniquads fly in close proximity and in a hostile RF environment. Out in the open this is still possible but unlikely, especially if the operator is staying well within the known range boundaries and line of sight.

Let’s imagine the operator has taken all possible precautions for this flight, just like a normal aircraft pilot would. The miniquad is in good shape: no damaged antennas, no questionable components. There is a contingency plan for video loss, control loss is unlikely. There is still an unknown chance that something will go wrong and the miniquad will somehow end up hitting the road. I can only speculate as to what could cause this, but let’s say it happens.

We are now in an uncommon scenario: we got unlucky and the quad is hitting the road. What would need to happen for someone to die? The typical miniquad weighs roughly 600 grams. A miniquad impacting a car cannot change its trajectory. What can it do? It could startle the driver, which in turn could lead to an accident. How likely is this? If we want to know, we would have to dive into statistics of traffic accidents and see how many of those were caused by unexpected hazards startling drivers. We would have to know the total number of events in which drivers were startled, and divide the known accidents by that to find the odds of an accident.

Let’s say that 99 out 100 times, when a car gets hit by an object the driver gets startled but no accident happens. It could be more or less, but the point is that an accident is not the most likely scenario when a driver gets startled. How about a fatal accident? That depends highly on the type of road and the road conditions. A miniquad landing on a car in gridlock traffic at rush hour is likely to cause some property damage, but extremely unlikely to result in a death.

Miniquad in park

When flying in a public place such as a park, the worst possible scenario is hitting an unexpected passerby with lethal force. Let’s examine what would need to happen for someone to die or get seriously injured in this case. Once again, the primary suspects are video loss, control loss and powertrain failure.

Most miniquad pilots make a good faith effort to avoid flying in populated areas. However, we don’t always fly in wide open spaces with no obstacles. Parks with trees are one example of a location where people can unexpectedly appear in the trajectory of a miniquad.

The number one mitigation factor for this type of risk is having a spotter continuously scanning the area for unexpected persons. This is not a protection when flying behind obstacles, as neither the spotter nor the operator would see behind, but it does decrease the odds of a collision. The second mitigating factor is a thorough pre-flight inspection of the miniquad to avoid loss of control, and a knowledge of the RF environment to avoid video loss. The third one is a contingency plan (“if I see a person in front of me I will immediately ground the quad and disarm”). The fourth (and arguably most important one) is speed. Because the energy of an object is proportional to the mass as well as the square of the velocity, a quad going 60 mph will impact with four times the energy of the same quad flying 30 mph. When flying in areas where humans are likely to appear, flying fast is flying irresponsibly in the same way driving above the speed limit is irresponsible.

Conclusion: if we as a community want the activity to be safer (not just appear to be safer, which is in itself a goal but not the point of this discussion), we need to think rationally and critically about the risks posed by miniquads. We need to inform ourselves regarding the likelihood of failures, and we have the responsibility to treat our quadcopters like regular aircraft. Flying a poorly maintained miniquad is irresponsible. Planning a flight adequately, thinking of the risks involved and having contingency plans is something all of us should do at all times.




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