Emerging sine-wave commutation techniques are advancing UAV efficiencies
Choosing the best form of motor control (ESC) for your drone.
Written by Mark Belbin, R&D at Agile Sensors, UUV developer with Eastern Edge Robotics
According to Gartner Research (2016), the largest inhibitor of drone adoption for commercial use is time in the air. Unmanned Aerial Vehicle (UAV) manufacturers are spending countless hours and financial resources trying to overcome this hurdle. Designing drones with advanced composite materials is expensive, and shoehorning batteries into every nook and cranny is only a band-aid fix that adds extra weight.
One area that is often overlooked, but could easily unlock efficiency gains for UAVs is in the propulsion system – specifically the electronic speed controller or ESC.
There are many options for brushless motor control in the drone industry. Choosing the ideal commutation method for your application may offer more efficiency increases than initially realized. Today there are two traditional methods for motor control: measuring back-EMF; and using Hall effect sensors. Both methods use trapezoidal motor commutation, a former industry standard. Trapezoidal commutation is inefficient for motor commutation and phase switching – which leads to uneven operation and a less efficient use of power. For a drone operator – that means less time in the air and less revenue.
Trapezoidal commutation switches current in the motor phases in six discrete steps. This is inherently inaccurate, having a rotor position margin of error of +/- 30 degrees. These inaccuracies add a torque ripple to the system, which negatively impacts efficiency and torque output of the motor.
However, a third method of motor control that is quickly emerging as the preferred industry choice is field oriented control or FOC. This method controls both the motor’s torque and speed independently through the use of sinusoidal commutation, resulting in strong efficiency gains, smooth control over a wide range of speeds, and increased torque output.
Until recently, FOC was neglected due to its computational complexity. However, advancements in technology have removed these barriers, leading to the rise of sine-wave driven commutation as the top choice for brushless motor applications.
Max Tubman is one of the top UAV pilots in North America. He is the CEO of BFD Systems, a company specialized in building custom UAS for heavy lift commercial operations.
“At BFD Systems we make big multirotors for heavy lift and endurance applications. Up until now we’ve been stuck with the same basic parameters. Heavier weight means bigger motors and more batteries, but the efficiency or lack of, has been a consistent barrier for our customers,” says Tubman.
“With the advancements in FOC motor control we are seeing significant increases in flight times and improvements in flight characteristics. With our larger propeller and motors combinations we are also seeing a major reduction in motor noise which is an added benefit. The screeching whine of back EMF controllers has been replaced with a silent motor and just the whoosh of the air through the propeller.”
In addition, sine-wave ESCs generate maximum torque over a wide range of speeds, as well as offering the benefit of quiet motor operation in comparison to traditional trapezoidal commutation. As UAVs integrate more and more into our daily routines, noise pollution will become a concern that must be monitored. The growth of passenger air travel was a driving factor behind noise-reduction regulations for many airports around the world, and the same can be expected for drone flight – especially as we expand the use of UAVs into more applications.
However, the benefits of FOC are not only limited to UAVs. A variety of brushless-dc motor applications can benefit from this type of control.
For unmanned underwater vehicles, quiet operation of the motor is crucial. Acoustic noise signatures penetrate aquatic environments effortlessly, making motor operation one of the leading causes of disturbance for marine wildlife. In addition, traditional motor control creates a less than ideal operating environment for sonar-based ocean mapping and surveying, as sound signatures collide causing interference.
So whether your drone requires more time in the air, increased torque, smooth sensorless-control, or noise reduction – take a break from researching the next best material composite or endurance battery and find a FOC controller for your commercial UAV application. You won’t be disappointed with the outcomes.