A Comprehensive Guide to Drone Motor Control Solutions

 

In a drone's core control system, the motor drive algorithm plays a crucial role-not only in flight stability and responsiveness, but also in endurance, noise levels, and overall cost structure. The two current mainstream control methods - FOC (field oriented control) and traditional square wave control (six-step commutation) - have different focuses in different levels of drone platforms. This article will analyze the differences and adaptation logic of these two solutions from four dimensions: principle, performance, application and development trend.

 

FOC control: pursuit of ultimate precision and efficiency

FOC (Field-Oriented Control) achieves precise electromagnetic torque control by converting three-phase current into magnetic field components (I_d and I_q) in a rectangular coordinate system. Its core advantages are:

· Sine wave drive: The current waveform is smoother and the harmonic distortion is less than 5%;

· wide speed ratio: supports 1:1000 speed regulation, covering from low-speed hovering to high-speed sudden flight;

· Extremely low torque fluctuation: torque output is more linear and flight is more stable;

· Fast response: A control loop of up to 50μs enables rapid torque adjustments.

 

Square wave control: simple, fast, cost-effective

Square wave control uses a fixed 120° commutation strategy and mainly relies on Hall sensors to determine the rotor position. The control method is more direct but has limited accuracy:

· Trapezoidal wave excitation: current harmonic distortion rate is as high as 20-30%;

· Limited speed range: the common ratio is 1:50;

· Torque ripple: noticeable vibration or sudden changes during hover or directional shifts.

· Hardware simplicity: No encoder is needed, resulting in low computational load and reduced cost.

 

Taking a certain model of consumer-grade drone (using FOC) and entry-level platform (using square wave) as examples, the key indicators are as follows:

Metric	FOC solution (high-end)	Square wave solution (basic)
Hover stability	±0.1 m	±0.5 m
Battery life	46 minutes	22 minutes
Noise Level	55dB	68dB
Wind disturbance response time	8 ms	35 ms
Motor temperature rise	+18℃	+32℃
Per-motor cost	$25	$8

 

 

Different types of UAVs have different requirements for power systems , so there are also obvious differences in the choice of control strategies.

 

Consumer drones: pursuit of stability and silence

Brands such as DJI and Autel generally adopt FOC solutions:

· High-precision hovering: FOC can reduce the difficulty of PID parameter adjustment and improve positioning stability;

· Better battery life: High-efficiency drive can improve the energy utilization rate of the whole machine by 8-12%;

· Silent flight: Sine wave drive reduces high frequency noise by 6-10dB.

 

FPV Racing Drones: Prioritizing Burst Power

In products that pursue speed and controllability, such as flying drones, square wave control is more cost-effective:

· Fast response: the response delay at full power output is only 0.2ms;

· Lightweight: Eliminating components like encoders significantly reduces system weight.

· Cost advantage: The overall drive system budget can be compressed to one-third of FOC.

 

Industrial drones: stability and precision first

In tasks such as agricultural spraying, inspection and mapping, extremely high control accuracy is required, and FOC is almost standard:

· Strong anti-disturbance: The motor output is more stable and can significantly suppress conductive vibration;

· Longer life: Reduce mechanical shock and increase bearing life by 3 to 5 times;

· Precise variable control: The speed regulation accuracy can be controlled within ±5RPM.

 

Hybrid Control Is Emerging as a New Trend

Some manufacturers have introduced flight status recognition mechanisms to achieve real-time switching of different control methods:

· Enable FOC during cruising to improve energy efficiency;

· Switch to square wave control to release instant torque during rapid acceleration/direction change;

· Comprehensive testing shows endurance improvements of around 9% while retaining more than 85% of the maneuverability.

 

Sensorless FOC quickly penetrates the mid-range market

With the help of new observer algorithms (such as sliding mode observer, flux estimation), the control accuracy of sensorless FOC has been significantly improved:

· The speed estimation error is reduced to less than 0.5%;

· Starting torque at zero speed can reach up to 30% of the rated torque.

· The cost per axis has dropped to $12, which is suitable for most mid-range UAV projects.

 

Hardware innovation continues to drive upgrades

· GaN power devices: Increase PWM frequency to 200kHz and reduce current ripple by 60%;

· Integrated driver IC: Such as TI DRV series, which integrates the driver and MCU to simplify the design and reduce costs by 40%.

 

Whether you prioritize FOC's precision and efficiency or the simplicity and cost-effectiveness of square wave control, they are all finding their place in different market dimensions. Current trends show:

· The high-end UAV market has basically achieved full coverage of FOC;

· The mid-range market is rapidly migrating to sensorless FOC;

· Square wave control is gradually concentrating on specific applications such as toys and racing.

 

The final selection should still return to the product itself: what kind of accuracy do you need? What cost can you accept? Do you have clear requirements for battery life and motor life?

 

As motor control strategies evolve and hardware capabilities advance, hybrid solutions combining FOC and square wave control are poised to become the industry standard.