FAQ

Why was the core of the SDK written in C++?

The aim was to have an API in a language which is cross-platform and has many language bindings. Additionally, the library needs to be lightweight and fast, so it does not slow down for onboard usage at higher rate messaging.

Are multiple vehicles supported?

Yes.

  • The MAVSDK C++ library allows C++ applications to connect to multiple vehicles at a time.
  • Python, Swift, and other language wrappers an only connect to a single vehicle at a time. However you can intantiate multiple copies of wrappers in order to connect to multiple systems.

A maximum of 255 vehicles can be connected.

The maximum number of vehicles is defined by the MAVLink protocol. MAVLink refers to vehicles as "systems", which are comprised of components (for example, a drone with a gimbal and a camera). Each system has a network-unique MAVLink system ID, with a value between 1 and 255 (0 is a "broadcast address"). Each component in a system shares its system id, and has a system-unique component ID, again with a value 1 and 255.

No. MAVSDK only supports MAVLink 2.0.

What sorts of vehicles are supported?

The MAVSDK API is designed for interacting with aircraft. It has primarily been tested for use with multicopters, but also has basic support for fixed wing and VTOL.

The API may "work" with ground-based or other types of vehicles, but some methods will not make sense. This use-case is mostly unsupported and untested.

Does MAVSDK support indoor use?

Indoor use is supported, however, some modes such as mission or position control are not available indoor, unless some additional positioning method is available (e.g. optical flow, visual-inertial odometry, a motion capture system, etc.).

Note that PX4 currently does not support missions in "local coordinates" i.e. meters but only "global coordinates i. e. latitude/longitude.

What UAV flight stacks are supported?

MAVSDK, so far, is optimised for use with the PX4 flight stack and all testing is done against PX4.

While many features should work on other flight stacks there may be implementation differences at the MAVLink microservices level that mean not every API will work. For example, PX4 and ArduPilot implement the parameter protocol differently, and vary slightly in the mission upload/download protocol (e.g. ArduPilot uses the 0 entry as the home position).

The SDK welcomes contributions to better support flight stacks other than PX4. We do however expect contributors to also help with testing and maintenance support for using the SDK with their autopilot.

Are serial connections supported?

Yes. Serial, TCP, and UDP connections are supported, see notes on connection.

Why is libCURL a dependency?

libCURL will be required to download the camera definition file which is referenced in CAMERA_INFORMATION. It might also come in handy whenever any other REST resources are required.

How are plugins added?

Check out C++/Contributing/Plugins.

Can a plugin depend on another one?

Yes - but it should not! The idea is that plugins don't have any coupling between each other which allows for any plugin to be changed or removed without breaking the rest. This will lead to some duplication at places, that's an acceptable trade-off. If the same code is used in many places, it can always be moved to core and get re-used from there.

Over time we have sometimes moved functionality from plugins to the core if it was exposed in multiple plugins (e.g. mission upload/download has been moved to the core so it can be used in the Mission plugin as well as the MissionRaw and Geofence plugins.

Can MAVSDK run on an embedded platform / microcontroller

MAVSDK is generally written a bit higher level, geared towards ARM devices such as a Raspberry Pi, smartphone or faster/better.

As it doesn't actually use too much compute, it could in theory be run on a microcontroller such as an ARM Cortex M4, however, it would require the POSIX APIs for serial and networking communication as well as the C++ standard library for things like std::thread or std::vector.

The recommendation for a microcontroller would be to use the pure C MAVLink headers.

The C++ MAVLink passthrough plugin basically exposes the direct C MAVLink API.

While it would be nice to have access to all MAVLink messages in the language wrappers, there are some technical challenges:

  • Essentially, it would mean that all MAVLink APIs would have to be duplicated by the proto APIs. This would increase the API and code size considerably.
  • Alternatively, the API could be exposed without types, using some sort of runtime access like get_message("ATTITUDE").get_field("pitch").as_float(). This would come with the cost of no type safety and runtime overhead for parsing the strings.

From a MAVSDK project point of view, there is also an advantage of not having a passthrough available in language wrappers; it encourages that required features are contributed back to the open-source project, rather than implemented in private using passthrough, and thus benefitting everyone.

© Dronecode 2017-2020. License: CC BY 4.0            Updated: 2021-04-14 07:04:25

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