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97 lines
5.0 KiB
Markdown
97 lines
5.0 KiB
Markdown
# CAN
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[Controller Area Network (CAN)](https://en.wikipedia.org/wiki/CAN_bus) is a robust wired network that allows drone components such as flight controller, ESCs, sensors, and other peripherals, to communicate with each other.
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Because it is designed to be democratic and uses differential signaling, it is very robust even over longer cable lengths (on large vehicles), and avoids a single point of failure.
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CAN also allows status feedback from peripherals and convenient firmware upgrades over the bus.
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PX4 supports two software protocols for communicating with CAN devices:
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- [DroneCAN](../dronecan/index.md): PX4 recommends this for most common setups.
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It is well supported by PX4, is a mature product with extensive peripheral support, and has had years of testing.
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- [Cyphal](https://opencyphal.org): PX4 support is a "work in progress".
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Cyphal is a much newer protocol which allows more flexibility and configuration, especially on larger and more complex vehicles.
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It has not yet seen significant adoption.
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::: info
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Both DroneCAN and Cyphal originate from an earlier project named UAVCAN.
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In 2022 the project split into two: the original version of UAVCAN (UAVCAN v0) was renamed to DroneCAN, and the newer UAVCAN v1 was renamed Cyphal.
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The differences between the two protocols are outlined in [Cyphal vs. DroneCAN](https://forum.opencyphal.org/t/cyphal-vs-dronecan/1814).
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:::
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:::warning
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PX4 does not support other CAN software protocols for drones such as KDECAN (at time of writing).
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:::
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## Wiring
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The wiring for CAN networks is the same for both DroneCAN and Cyphal/CAN (in fact, for all CAN networks).
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Devices are connected in a chain in any order.
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At either end of the chain, a 120Ω termination resistor should be connected between the two data lines.
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Flight controllers and some GNSS modules have built in termination resistors for convenience, thus should be placed at opposite ends of the chain.
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Otherwise, you can use a termination resistor such as [this one from Zubax Robotics](https://shop.zubax.com/products/uavcan-micro-termination-plug?variant=6007985111069), or solder one yourself if you have access to a JST-GH crimper.
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The following diagram shows an example of a CAN bus connecting a flight controller to 4 CAN ESCs and a GNSS.
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The diagram does not show any power wiring.
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Refer to your manufacturer instructions to confirm whether components require separate power or can be powered from the CAN bus itself.
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For more information, see [Cyphal/CAN device interconnection](https://wiki.zubax.com/public/cyphal/CyphalCAN-device-interconnection?pageId=2195476) (kb.zubax.com).
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While the article is written with the Cyphal protocol in mind, it applies equally to DroneCAN hardware and any other CAN setup.
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For more advanced scenarios, consult with [On CAN bus topology and termination](https://forum.opencyphal.org/t/on-can-bus-topology-and-termination/1685).
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### Connectors
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Pixhawk standard compatible CAN devices use 4 pin JST-GH connectors for CAN.
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Two connectors are used for input and output when wiring in a chain (except for flight controllers and some GNSS devices with builtin termination, which only have a single JST-GH connector).
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Other (non-Pixhawk compatible) devices may use different connectors.
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However, as long as the device firmware supports DroneCAN or Cyphal, it can be used.
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### Redundancy
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DroneCAN and Cyphal/CAN support using a second (redundant) CAN interface.
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This is completely optional but increases the robustness of the connection.
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All 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.
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## Firmware
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CAN peripherals may run proprietary or open source firmware (check manufacturer guides to confirm the required setup).
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PX4 can be built to run as open-source DroneCAN firmware on supported CAN hardware.
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See [PX4 DroneCAN Firmware](../dronecan/px4_cannode_fw.md) for more information.
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## Support and Configuration
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[DroneCAN Setup and Configuration](../dronecan/index.md)
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[PX4 DroneCAN Firmware](../dronecan/px4_cannode_fw.md)
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## Videos
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### DroneCAN
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Intro to DroneCAN (UAVCANv0) and practical example with setup in QGroundControl:
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<lite-youtube videoid="IZMTq9fTiOM" title="Intro to DroneCAN (UAVCANv0) and practical example with setup in QGroundControl"/>
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### Cyphal
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UAVCAN v1 for drones (Cyphal) — PX4 Developer Summit Virtual 2020
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<lite-youtube videoid="6Bvtn_g8liU" title="UAVCAN v1 for drones — PX4 Developer Summit Virtual 2020"/>
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---
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Getting started using UAVCAN v1 with PX4 on the NXP UAVCAN Board — PX4 Developer Summit Virtual 2020
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<lite-youtube videoid="MwdHwjaXYKs" title="Getting started using UAVCAN v1 with PX4 on the NXP UAVCAN Board"/>
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---
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UAVCAN: a highly dependable publish-subscribe protocol for hard real-time intra-vehicular networking — PX4 Developer Summit Virtual 2019
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<lite-youtube videoid="MBtROivYPik" title="UAVCAN: a highly dependable publish-subscribe protocol for hard ..."/>
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