CAN (DroneCAN & Cyphal)

Controller Area Network (CAN) is a robust wired network that allows drone components such as flight controller, ESCs, sensors, and other peripherals, to communicate with each other.

It is particularly recommended on larger vehicles.

综述

CAN it is designed to be democratic and uses differential signaling. For this reason it is very robust even over longer cable lengths (on large vehicles), and avoids a single point of failure. CAN 还允许来自外设的状态反馈，并通过总线方便的进行固件升级。

PX4 支持与 CAN 设备通信的两个软件协议：

• DroneCAN: PX4 推荐大多数常见的设置。 它得到了 PX4 的很好支持，是一个成熟的产品，具有广泛的外围支持，并经过多年的测试。
• Cyphal：PX4 支持是一个“在进行中的工作”。 Cyphal 是一种更新的协议，允许更多的灵活性和配置，尤其是对于较大和较复杂的载具。 它还没有被广泛应用。

INFO

DroneCAN 和 Cyphal 都是早先一个叫做UAVCAN的项目。 在2022年，该项目分为两个部分：原始版本的 UAVCAN (UAVCAN v0) 更名为 DroneCAN，较新的 UAVCAN v1 更名为 Cyphal。 这两项协议之间的差异在Cyphal vs. DroneCAN中作了概述。

PX4不支持KDECAN等无人驾驶飞机的其他CAN软件协议(撰写时)。

布线

CAN 网络的接线对于 DroneCAN 和 Cyphal/CAN 是一样 (实际上对所有的 CAN 网络都一样)。

Devices within a network are connected in a daisy-chain in any order (this differs from UARTs peripherals, where you attach just one component per port).

WARNING

Don't connect each CAN peripheral to a separate CAN port! Unlike UARTs, CAN peripherals are designed to be daisy chained, with additional ports such as CAN2 used for redundancy.

在链的任一端，应该在两个数据线之间连接一个 120Ω 的终端电阻。 飞控和一些 GNSS 模块为了方便使用内置了终端电阻， 因此应该放在链的终端。 否则，你可以使用终端电阻，比如 Zubax Robotics 的这款。如果你有JST - GH压接工具，也可以自己焊接一个。

下图显示了一个 CAN 总线连接飞控到 4 个 CAN 电调和一个 GNSS 的示例。 It includes a redundant bus connected to CAN 2.

图中未显示任何电源接线。 参考制造商的说明，确认组件是否需要单独供电，还是可以通过 CAN 总线供电。

INFO

For more information, see Cyphal/CAN device interconnection (kb.zubax.com). 虽然本文是以 Cyphal 协议为基础编写的，但同样适用于 DroneCAN 硬件和任何其他 CAN 设置。 如需了解更复杂的场景，请参考 论CAN总线拓扑结构与终端匹配。

连接器

Pixhawk标准兼容的 CAN 设备使用 4 引脚的 JST-GH 连接器为 CAN。 在连线接线时，有两个连接器用于输入和输出（飞行控制器除外和一些内置终止的全球导航卫星系统（GNSS）设备除外）； 它仅有一个JST-GH连接器)。

其他(非Pixhawk兼容的)设备可能使用不同的连接器。 然而，只要设备固件支持DroneCAN 或Cyphal，它就可以使用。

冗余

DroneCAN 和 Cyphal/CAN支持使用第二个(冗余) CAN 接口。 这是完全可选的，但会增加连接的强度。

Pixhawk flight controllers come with 2 CAN interfaces; if your peripherals support 2 CAN interfaces as well, it is recommended to wire both up for increased safety.

Flight Controllers with Multiple CAN Ports

Flight Controllers may have up to three independent CAN ports, such as CAN1, CAN2, CAN3 (neither DroneCAN or Cyphal support more than three). Note that you can't have both DroneCAN and Cyphal running on PX4 at the same time.

TIP

You only need one CAN port to support an arbitrary number of CAN devices using a particular CAN protocol. Don't connect each CAN peripheral to a separate CAN port!

Generally you'll daisy all CAN peripherals off a single port, and if there is more than one CAN port, use the second one for redundancy. If three are three ports, you might use the remaining network for devices that support another CAN protocol.

The documentation for your flight controller should indicate which ports are supported/enabled. At runtime you can check what DroneCAN ports are enabled and their status using the following command on the MAVLink Shell (or some other console):

uavcan status

Note that you can also check the number of supported CAN interfaces for a board by searching for CONFIG_BOARD_UAVCAN_INTERFACES in its default.px4board configuration file.

固件

CAN 外围设备可以运行专有或开源固件(请检查制造商指南以确认所需的设置)。

PX4 可以构建在支持的 CAN 硬件上作为开源的 DroneCAN 固件运行。 更多信息请参考 PX4 DroneCAN 固件。

支持和配置

DroneCAN 设置和配置

PX4 DroneCAN 固件

视频

DroneCAN

关于 DroneCAN (UAVCANv0) 的介绍和在 QGroundControl 中设置的实用示例：

Cyphal

无人机的 UAVCAN v1 (Cyphal) - PX4 开发者峰会虚拟2020

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在NXP UAVCAN板上使用UAVCAN v1和PX4入门——2020年PX4开发者峰会线上会议

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UAVCAN：一个高度可靠的发布-订阅协议，用于硬实时车辆内网络 — PX4 开发者虚拟峰会 2019