Modern drones can do much more than simply respond to commands from a remote controller.
To stay stable, understand their movement and avoid nearby objects, drones can combine information from GPS, motion sensors, cameras, optical flow systems and obstacle-detection sensors with onboard flight-control software.
So, how do drones navigate and avoid obstacles?
In simple terms, sensors collect information about the drone and its surroundings, navigation software works out what that information means, and the flight controller adjusts the motors to keep the aircraft moving in the intended direction.
The exact technology varies considerably between different drones. If you’re new to how these toys are controlled, read about how remote control toys work first.
What Is a UAV Drone?
The terms drone and UAV are often used for aircraft that operate without a pilot physically sitting inside them.
UAV stands for unmanned aerial vehicle.
The aircraft itself is only part of the system. A working drone may also rely on a controller, sensors, flight electronics, navigation software and communication equipment.
That matters because navigation is not performed by the frame or motors alone. Several electronic systems work together to keep the aircraft controlled during flight.
How Do Drones Navigate?
Before a drone can follow a route or hold its position, it needs some way to estimate where it is and how it is moving.
Different drones can use combinations of:
- GPS or other satellite positioning
- Gyroscopes
- Accelerometers
- Compass or magnetometer data
- Barometric altitude measurements
- Cameras
- Optical flow sensors
- Rangefinders
- Other positioning sensors
The flight-control system can combine information from several of these sources instead of relying entirely on one sensor.
A simple way to understand the process is:
Sensors collect data → navigation software estimates movement and position → flight controller adjusts the motors
For example, if the drone begins tilting unexpectedly, motion sensors can detect the change and the flight controller can adjust motor speeds to help stabilize it.
GPS adds another layer by providing global position information outdoors when a reliable satellite signal is available.
How Do Drones Avoid Obstacles?
Drone obstacle avoidance starts by detecting objects near the aircraft.
Different drones may use different technologies for this job, including:
- Cameras
- Depth sensors
- Lidar
- Sonar
- Radar-based distance sensors
- Other rangefinding systems
These sensors can estimate how close an object is to the drone.
The flight-control system can then use that information to respond.
Depending on the drone and its software, that response might mean:
stopping before the obstacle, restricting movement toward it, moving around it, or calculating another route.
Not every obstacle-avoidance system has the same capabilities.
A drone with only forward-facing detection cannot monitor its surroundings in the same way as a model with sensors facing several directions.
What Is Optical Flow on a Drone?
Cameras are not only used to record photos and videos.
Some drones use visual information to help estimate movement.
One example is optical flow.
Optical flow looks at changes in the visual scene beneath or around the aircraft to estimate how the drone is moving relative to the surface.
A downward-facing camera may repeatedly observe the ground. As the patterns in the image shift, the flight system can use those changes to estimate movement.
This can help with local positioning, particularly when satellite positioning is unavailable or unreliable.
Is Optical Flow the Same as Obstacle Avoidance?
No.
These two features are related to drone navigation, but they serve different purposes.
Optical flow mainly helps estimate movement relative to a visible surface.
Obstacle avoidance focuses on detecting nearby objects and helping the aircraft respond to them.
A drone can therefore have optical-flow positioning without having full obstacle avoidance, or obstacle-detection hardware without relying on optical flow for positioning.
For example, our compact foldable drone, the Folding UAV with Optical Flow and Dual Camera System, currently lists both optical-flow positioning and four-side obstacle avoidance as separate features.
Another example is the S96 Mini Pocket Drone, which includes an optical-flow version.
How Do Drones Navigate Without GPS?
GPS is useful, but it is not the only way a drone can estimate movement.
So how do drones navigate without GPS?
They can use other sources of information to build a local estimate of their position and motion.
Possible technologies include:
- Optical flow
- Cameras
- Inertial sensors
- Visual-inertial positioning
- External positioning systems
One method is Visual Inertial Odometry, often shortened to VIO.
VIO combines visual information from cameras with measurements from inertial sensors to estimate movement, orientation and local position.
Optical flow can also help determine how the drone is moving relative to the ground.
There is an important difference, though.
GPS can provide a position in a global coordinate system.
A vision-based system may instead know that the drone has moved several metres from its starting point without necessarily knowing its exact geographic location.
So navigation without GPS does not automatically mean global positioning without GPS.
How Do Drones Navigate Autonomously?
Autonomous drone navigation goes beyond simply keeping the aircraft stable.
An autonomous system can estimate its position, follow a planned objective and react to information from its surroundings with less direct input from a pilot.
Depending on the aircraft, this could involve:
- Following a planned route
- Holding a position
- Detecting obstacles
- Stopping before an obstruction
- Adjusting a route around an obstacle
More advanced path-planning systems can use obstacle information when deciding where the aircraft should move next.
Autonomous navigation should not be confused with ordinary remote-controlled flight.
Even a manually controlled drone can use automatic stabilization to keep itself level. That does not necessarily mean the aircraft can independently plan and complete a route.
How Do Drone Sensors Work Together?
A major part of drone navigation is sensor fusion.
Instead of trusting one sensor completely, the flight-control software can compare information from several sources.
Imagine a drone flying outdoors.
GPS may estimate its geographic position.
The gyroscope can measure rotation.
Accelerometers can detect changes in movement.
A barometer may help estimate altitude.
Cameras or optical flow can provide visual movement information.
Obstacle sensors can detect nearby objects.
The software combines useful information from these sources to build a better estimate of what the drone is doing.
That estimate is then used to control the motors.
Can Drones Avoid Every Obstacle?
No.
Obstacle avoidance can reduce risk, but it does not make a drone impossible to crash.
Sensors have limits.
Their performance can depend on factors such as:
- Detection distance
- Direction and field of view
- Object size
- Surface characteristics
- Lighting conditions for camera-based systems
- Flight speed
- Sensor placement
- Software behavior
A sensor can only react to an object it can actually detect.
That is why terms such as optical flow, obstacle avoidance, GPS positioning and autonomous navigation should not be treated as interchangeable features when comparing drones.
If you want to explore different recreational RC vehicles and flying toys, browse our Remote Control Toys collection.
You can also see a different style of flying toy in our 2-in-1 RC Flying Car Drone, which combines ground and flight modes. For a bird-shaped flyer, see our remote control bird.
Frequently Asked Questions
Do all drones use GPS?
No.
Some drones use GPS or other satellite positioning, while others can rely on different combinations of cameras, optical flow, inertial sensors or external positioning systems.
The exact setup depends on the drone.
How do drones know an obstacle is nearby?
Obstacle-detection sensors estimate the distance between the drone and nearby objects.
Depending on the aircraft, this can involve cameras, lidar, sonar, radar or other rangefinding technologies.
The flight-control software can then use that information to stop or adjust the aircraft's movement.
Is optical flow the same as obstacle avoidance?
No.
Optical flow is mainly used to estimate movement using visual information, while obstacle avoidance is designed to detect objects around the aircraft and react to them.
Can drones fly autonomously without GPS?
Some drone systems can perform local navigation without GPS using technologies such as optical flow, visual-inertial positioning or external positioning.
The exact capability depends on the drone's hardware and software.
How do drones navigate indoors?
Indoor navigation can be more difficult because GPS signals may be weak or unavailable.
Some drones can instead use optical flow, cameras, inertial sensors or external positioning systems to estimate local movement and position.
Does obstacle avoidance mean a drone cannot crash?
No.
Obstacle avoidance is an assistance system with limits. Objects outside the sensors' detection area, difficult environmental conditions or other limitations can still lead to collisions.
How Drone Navigation Works in Simple Terms
So, how do drones navigate and avoid obstacles?
The aircraft combines information from different sensors with flight-control software.
GPS can help determine global position.
Motion sensors help track movement and orientation.
Optical flow and cameras can support local positioning.
Obstacle sensors detect nearby objects.
The flight controller then uses that information to adjust the motors and control how the aircraft moves.
The important thing to remember is that navigation, optical flow, GPS positioning and obstacle avoidance are connected technologies, but they are not the same feature.
