Quadrotor safety system offers protective interference against rotor mishaps

Quadrotor safety system offers protective interference against rotor mishaps

Drone watchers are talking about a neat idea that has emerged from a prototype by researchers from Australia's University of Queensland, in Brisbane, Australia. They have worked on a rotor safety system for small UAVs (quadrotors).

They call their solution the Safety Rotor and it delivers a solution to guard against the risk of accidents involving the spinning blades. Stop those rotors! Their solution obeys.

Spinning hoops, electromagnetic braking, feature in this solution.

"A cage around the propellers spins more slowly than the propellers and is constantly on the lookout for biological material approaching the blades," said John Biggs in TechCrunch.

The blades are enclosed by a hoop, passively rotating around the same axis as the blades. Any object interfering with the hoop results in a decrease in speed at which the hoop is spinning.

IEEE Spectrum's Evan Ackerman: "It's a simple idea: A plastic hoop is added to the system that spins around the rotor plane, such that anything that would make contact with the rotor must make contact with the hoop first. And if the hoop senses a contact, it puts the brakes on the rotor, slowing it enough that it'll turn needing a finger into needing a band-aid."

A safety circuit decelerates all rotors. As a result, the blades turn harmless by the time the object—such as a hand— would make contact or else change the motion of the craft away from the object to avoid collision. Blades are stopped from spinning, in less than 0.06 of a second from the time that the finger touches the hoop, said New Atlas.

The hoop that is fitted around the blades is made of rigid or semi-rigid material. Its rotation speed is fast enough to effectively form an enclosed shell around the blades, but not too fast to be considered an additional hazard. A sensor measures the rotation speed of the hoop and any slowdown in rotation triggers the immediate braking of all rotors.

UniQuest provided details on features, and said that "The hoop that is fitted around the blades is made of rigid or semi-rigid material. Its rotation speed is fast enough to effectively form an enclosed shell around the blades, but not too fast to be considered an additional hazard. A sensor measures the rotation speed of the hoop and any slowdown in rotation triggers the immediate braking of all rotors."

A video that presents their Safety Rotor notes that high-speed rotors can be dangerous; even small rotors can injure people. Injuries may be serious. They may range from lacerations to even amputations and loss of vision. The video presenter said drones operating around suburbs and population centers should be cause for concern.

But wait. Who would be so daft to put one's hand directly in front of the spinning blades? That's not the problem.

Evan Ackerman in IEEE Spectrum: "Not running into people with your drone is generally good advice, but the problems tend to happen when for whatever reason the drone escapes from your control. Maybe it's your fault, maybe it's the drone's fault, but either way, those spinny bits can cause serious damage."

Typical rotors spin at 4000-8000 RPM. The protective method that the researchers propose re-uses existing structures. They said their solution can be easily retrofitted in existing quadrotors.

They give a detailed account of their solution and testing results in their ICRA 2018 paper, "The Safety Rotor—an Electromechanical Rotor Safety System for Drones" by P Pounds and W Deer. The team was led by Dr. Paul Pounds, said Ben Coxworth in New Atlas.

According to UniQuest, the safety rotor came out of Pounds' Robotics Design Laboratory in the School of Information Technology and Electrical Engineering. (UniQuest Pty Limited is a university commercialization entity, managing the intellectual property of The University of Queensland.)

Coxworth referred to "those fast-spinning and potentially skin-slicing rotor blades."

What's next? Pounds' team recently presented Safety Rotor at the 2018 International Conference on Robotics and Automation, and is now looking for partners interested in commercializing the system, Coxworth said.

Ackerman commented that their quadrotor-safety system managed to be "highly effective, reliable, lightweight, and cheap all at the same time."

UniQuest, meanwhile, noted the system uses low-cost off-the-shelf components combined with a low-cost plastic manufacturing process.

More information: uniquest.com.au/safety-rotor-r … ircraft-systems-rpas

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May 29, 2018
It might be wise to stop the opposite rotor at the same time to maintain stablity/balance of the drone during the incident.

May 29, 2018
"A sensor measures the rotation speed of the hoop and any slowdown in rotation triggers the immediate braking of all rotors."


That's going to make maneuvering the copter mighty difficult, because the free-spinning hoop is a gyroscope and will change its relative motion when the quadcopter changes direction or orientation.

For example, if a gust of wind throws the copter sideways, swinging one way causes the cage to appear to speed up, while going the other way causes the cage to appear to slow down. As the copter swings and returns back, at some point the system's going to detect the cage slowing down and hit the brakes, then drop out of the sky.

May 29, 2018
"A sensor measures the rotation speed of the hoop and any slowdown in rotation triggers the immediate braking of all rotors."


That's going to make maneuvering the copter mighty difficult, because the free-spinning hoop is a gyroscope and will change its relative motion when the quadcopter changes direction or orientation.

For example, if a gust of wind throws the copter sideways, swinging one way causes the cage to appear to speed up, while going the other way causes the cage to appear to slow down. As the copter swings and returns back, at some point the system's going to detect the cage slowing down and hit the brakes, then drop out of the sky.

I'm pretty sure that by them saying "any slowdown in rotation" means whacking a finger and stopping abruptly or having a major change in speed there, big guy.

May 29, 2018
"I'm pretty sure that by them saying "any slowdown in rotation" means whacking a finger and stopping abruptly or having a major change in speed there, big guy.


The way they're detecting movement is by measuring whether the cage passes the sensor. Measuring a change in speed requires the cage to make a full rotation, so the system can measure the interval.

So, for about 99% of the time, the system does not have any way to know whether the cage has stopped or merely slowed down. It expects to get a pulse at regular intervals, and if the pulse is significantly delayed it must assume the cage has stopped rotating. Waiting a millisecond too long means someone loses fingers.


May 29, 2018
For example, the 60 ms reaction time means that a copter moving at 1 m/s will advance 6 cm by the time the rotors have stopped. That's enough to chop off your fingers, which is why the cage extends further out from the rotor.

Every millisecond of delay means 1 millimeters off of your fingers. If the cage is rotating at some safe speed, let's say 20 revolutions a second, it takes an additional 5 centimeters to detect a missing pulse, so, if the pulse isn't there in time it must be assumed that the cage has stopped.

Detection speed can be improved, but then the cage becomes a hazard in itself. 20 rps is already 1200 RPM which is like sticking your finger in a computer fan. 200 rps (5 mm delay) is 12000 RPM which is like sticking your finger in a weedwhacker.

May 29, 2018
Besides, in certain moves the copter might make, the freely rotating cage will stop relative to the body of the copter, or even reverse rotation, which makes the system drop out of the sky.

Another disadvantage is that in a quadrotor the blades aren't necessarily far enough apart and the cage will hit the other blades, or the body of the quadrotor.

May 29, 2018
"It might be wise to stop the opposite rotor at the same time to maintain stablity/balance of the drone during the incident. "

That is not going to help. Two rotors cannot keep the drone stable and since you just hit something there is basically a fixed point (the contact point) around which the drone will start to pivot.

May 30, 2018
"That is not going to help."


It's actually necessary to do it. The complementary rotor pair is counter-rotating to null out the reaction torque that would cause the quadrotor to spin in place. If you suddenly brake just one rotor, it causes a torque impulse that flicks the copter around like a frisbee.


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