Next Level Drone Safety: M300 RTK Three Propeller Emergency Landing

An extra line of safety for your peace of mind

By DJI Enterprise DJI Enterprise
September 4, 2020

When you see it for the first time, the new Three Propeller Emergency Landing Mode looks both impressive and also somewhat odd. The mode puts the drone into a rapid spin, where it begins rotating between two and three times per second. That’s right, the entire drone spins while flying until it’s back on the ground. 

And in that rotation is its salvation. The rapid spinning allows the motors to distribute their thrust more evenly beneath the drone, allowing it to maintain relative stability. Because the arm with the non-functioning motor is never in one place for long, it’s impossible for the drone to start dropping at that arm. In fact, once the spinning is underway the Matrice 300 RTK is a bit like a gyroscope or a flywheel. 

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And while it looks pretty unusual, this is actually quite remarkable: The Matrice 300 RTK is able to do what has historically been impossible for a quadcopter: Fly with three motors. 

Sounds amazing, right? It is. Just watch. 

Motor Failure and Stabilization

"Three Propeller Emergency Landing Mode"

If you’ve been around quadcopters for any time, you’ll know the harsh truth: If one motor fails your UAS is going to drop out of the sky. And not with a gentle flutter, either. Your drone is going down, pretty much as fast as gravity can pull it toward the ground. The end of that fall – the crash – is not going to be pretty. 

That distant but very real risk of failure is why some people have traditionally opted for hexacopters like the Matrice 600 platform. When one of its six motors fails, a drone can still be brought safely back to the ground by a decent pilot. But not when there are just four motors. Then, even the best pilot imaginable can’t save it from the inevitable. 

 

“Normally speaking, if you lose the thrust of one propeller – the three remaining propellers cannot provide the drone with enough thrust,” explains DJI’s Freda Peng, a Senior Product and Solution manager with DJI. “And those three propellers cannot maintain the drone in stable flight.” 

While that kind of risk might be acceptable for a home-built unit or an inexpensive consumer quadcopter, it’s another situation in the world of enterprise drones. With higher-end sensors, like the H20 Series, LiDAR, and high-powered optical zooms, the stakes are much higher. These drones are expensive machines with pricey extras – such as Real-Time Kinematic (RTK) technology for greater spatial accuracy. They are also in constant demand on industrial job sites, where downtime just isn’t an option. 

Odds of failure low

Of course, DJI products are built to last. And the odds of having a malfunction with a propulsion system are very low. In fact, DJI engineers have calculated that the odds of a motor or ESC failure are around 0.01 per cent. Those are pretty low odds.

But failures can happen – especially when drones are operating in the rough-and-tumble environments that define many industrial jobs. As a result, DJI decided that it would be useful to add a critical feature to its new Matrice 300 RTK platform. Using software in conjunction with its flight control board, the Matrice 300 RTK has a lifesaving feature.

How It Works

On any drone, the flight controller is working all the time. One of its key tasks is to ensure stable flight. It does this by constantly checking onboard sensors to ensure the drone is level – and also by constantly monitoring the RPMs of all motors. In conjunction with the Electronic Speed Controllers or ESCs, it is continuously speeding up and slowing down the motors to ensure that the drone is always rock steady in the air. These system checks take place several hundred times each second, with minute adjustments constantly taking place. 

With the Matrice 300 RTK, the flight controller and other specialized software algorithms now do something entirely new and unprecedented for a DJI quadcopter: If they sense that the drone has lost power in a motor, or that a motor is rotating enough below speed to cause a stability problem, the flight controller takes over. It puts the drone into an emergency survival mode designed to bring the machine down safely – or to allow the pilot to manually guide the Matrice 300 RTK to a safer location for a landing.

 

Fast First Responder

You could think of this hardware and software package, in some ways, as a First Responder. The flight control board can detect a motor anomaly in less than 100 milliseconds. An additional 100 milliseconds buffer is allowed to avoid false fault detection before automatically transitioning into the Three Propeller Emergency Landing Mode. Any longer than 200 milliseconds and the drone’s angular speed would be too high to control – a major obstacle in controlled three propeller emergency landing. The M300 RTK’s upgraded flight control algorithms have all but eliminated any lag before the software takes over to put the drone into its life-saving spin. 

Not surprisingly, there’s some drift that occurs as a result of all of that rotational energy. The Matrice 300 RTK could drift some 30 meters before it’s brought down to the ground. It doesn’t actually land while spinning, however. The pilot uses a special joystick command to cut the engines once the Matrice 300 RTK is very close to the ground – and hopefully a softer surface like grass. 

“We continue to test and optimize,” says Peng. “So engineers will continue to update this feature.” 

Controlled Landing

An Matrice 300 RTK First

According to DJI’s Freda Peng, this feature had been planned for the Matrice 300 RTK from the beginning. Though definitely an engineering challenge, DJI knew this was a feature that customers would welcome – especially on a higher-end enterprise model.

At the moment, this feature is available only on the Matrice 300 RTK. Peng says it’s possible it will make its way to other DJI products, but the focus for now is on the Matrice 300 RTK.

DJI has written a White Paper which outlines in greater detail how the process works. You can find that here

Remarkable

It’s amazing to see how this feature has gone from a concept to an engineering reality. It will be even more amazing as we get some reports of this actually saving a Matrice 300 RTK in the workplace.

The odds are low that a Three Propeller Landing will ever be needed by most Matrice 300 RTK users. But for those rare occasions when something does go terribly wrong...this autonomous feature can make it right. 

Learn more about the safety features packed into the M300 RTK. 

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