Cyphal communicator

Cyphal communicator is a ROS package that connects the Cyphal HITL autopilot interface and a simulator interface (based on ROS, ArduPilot JSON, etc).

Purpose

The Cyphal communicator is primailry intended for ArduPilot/PX4 Cyphal HITL simulation, but it can be used for other purposes as well.

Minimal technical requirements

• Communicator node: ROS-noetic, ubuntu 20.04
• Autopilot hardware: CUAV V5+
• CAN-sniffer: handle at least 2500 CAN frames/sec

Content

• 1. Communicator Cyphal and ROS Interfaces
  • 1.1. Minimal quadcopter interface
  • 1.2. Extended interface
• 2. PX4 Cyphal interface
• 3. Disign
• 4. Redundancy
• 5. Installation
• 6. Running
• 7. Usage example

1. Communicator Cyphal and ROS Interfaces

Cyphal interface on the communicator node can be illustrated with Yukon gui tool as shown below:

Here green topics are publishers, red topics are subscribers, gray topics are RPC-services.

1.1. Minimal quadcopter interface

The following Cyphal interface is supported for a minimal quadrotor application:

1. Actuator

Cyphal interface:

Interface	Communicator's Port	Message
udral/actuator	sub.setpoint sub.readiness pub.feedback	udral.service.actuator.common.sp.Vector31 reg.udral.service.common.Readiness zubax.telega.CompactFeedback

ROS-interface for necessary setpoint and readiness:

flowchart LR

setpoint[ setpoint, reg.udral.service.actuator.common.sp.Vector8] --> F(SetpointCyphalToRos) --> actuators_raw[ /uav/actuators_raw, sensor_msgs/Joy]
readiness[ readiness, reg.udral.service.common.Readiness] --> R(ReadinessCyphalToRos) --> arm[ /uav/arm, std_msgs::Bool]

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ROS-interface for auxilliary ESC feedback:

flowchart LR
esc_status[ /uav/esc_status, mavros_msgs/ESCTelemetryItem] --> EscStatusRosToCyphal(EscStatusRosToCyphal)
EscStatusRosToCyphal --> esc_feedback_0[ esc_feedback_0, zubax.telega.CompactFeedback]
EscStatusRosToCyphal --> esc_feedback_n[ ...]
EscStatusRosToCyphal --> esc_feedback_7[ esc_feedback_7, zubax.telega.CompactFeedback]

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2. IMU

Cyphal interface:

Interface	Communicator's Port	Message
imu	pub.accelerometer pub.gyro	uavcan.si.sample.acceleration.Vector3 uavcan.si.sample.angular_velocity.Vector3

ROS-interface:

flowchart LR

imu[ /uav/imu, sensor_msgs/Imu] --> F(ImuRosToCyphal)
F(ImuRosToCyphal) --> gyro[ gyro, uavcan.si.sample.angular_velocity.Vector3]
F(ImuRosToCyphal) --> accel[ accel, uavcan.si.sample.acceleration.Vector3]

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3. Magnetometer

Cyphal interface:

Interface	Communicator's Port	Message
Magnetometer	pub.mag	uavcan.si.sample.magnetic_field_strength.Vector3

ROS-interface:

flowchart LR

imu[ /uav/mag, sensor_msgs/MagneticField] --> F(MagRosToCyphal) --> mag[ mag, uavcan.si.sample.magnetic_field_strength.Vector3]

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4. Barometer

Cyphal interface:

Interface	Communicator's Port	Message
Barometer	pub.pressure pub.temperature	uavcan.si.sample.pressure.Scalar uavcan.si.sample.temperature.Scalar

ROS-interface:

flowchart LR

static_temperature[ /uav/static_temperature, std_msgs/Float32] --> BaroRosToCyphal(BaroRosToCyphal) --> baro_temperature[ baro_temperature, uavcan.si.sample.temperature.Scalar]

static_pressure[ /uav/static_pressure, std_msgs/Float32] --> BaroRosToCyphal --> baro_pressure[ baro_pressure, uavcan.si.sample.pressure.Scalar]

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5. GNSS

Cyphal interface:

Interface	Communicator's Port	Message
udral/gnss	pub.point pub.status pub.sats pub.pdop	reg.udral.physics.kinematics.geodetic.PointStateVarTs uavcan.primitive.scalar.Integer16 uavcan.primitive.scalar.Integer16 uavcan.primitive.scalar.Integer16

ROS-interface:

flowchart LR
yaw[ /uav/yaw, std_msgs/Float32] --> GpsRosToCyphal(GpsRosToCyphal) --> gps_yaw[ gps_yaw, uavcan.si.sample.angle.Scalar]

point[ /uav/gps_point, sensor_msgs/NavSatFix] --> GpsRosToCyphal
GpsRosToCyphal --> gps_status[ gps_status, uavcan.primitive.scalar.Integer16]
GpsRosToCyphal --> gps_point[ gps_point, reg.udral.physics.kinematics.geodetic.PointStateVarTs]

velocity[ /uav/velocity, geometry_msgs/Twist] --> GpsRosToCyphal --> gps_point[ gps_point, reg.udral.physics.kinematics.geodetic.PointStateVarTs]

GpsRosToCyphal --> gps_sats[ gps_sats, uavcan.primitive.scalar.Integer16]
GpsRosToCyphal --> gps_pdop[ gps_pdop, uavcan.primitive.scalar.Integer16]

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1.2. Extended interface

The following Cyphal allows to run VTOL application and add a few auxilliary features:

6. RGB LED

Cyphal interface:

Interface	Communicator's Port	Message
Udral/rgbled	sub.rgbled	reg.udral.physics.optics.HighColor

ROS-interface not supported yet

7. Airspeed (including Differential Pressure)

Cyphal interface:

Interface	Communicator's Port	Message
udral/airspeed	pub.aspd.cas pub.aspd.tas pub.aspd.dpres pub.aspd.temperature	uavcan.si.sample.velocity.Scalar uavcan.si.sample.velocity.Scalar uavcan.si.sample.pressure.Scalar uavcan.si.sample.temperature.Scalar

ROS-interface for Airspeed:

flowchart LR
tas[ /uav/airspeed/tas, std_msgs/Float32] --> AirspeedRosToCyphal(AirspeedRosToCyphal)
cas[ /uav/airspeed/cas, std_msgs/Float32] --> AirspeedRosToCyphal(AirspeedRosToCyphal)
cas[ /uav/static_temperature, std_msgs/Float32] --> AirspeedRosToCyphal(AirspeedRosToCyphal)
AirspeedRosToCyphal --> aspd_tas[ aspd.tas, uavcan.si.sample.velocity.Scalar]
AirspeedRosToCyphal --> aspd_cas[ aspd.cas, uavcan.si.sample.velocity.Scalar]
AirspeedRosToCyphal --> aspd_temp[ aspd.temp, uavcan.si.sample.temperature.Scalar]

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ROS-interface for Differential Pressure:

flowchart LR
dpres[ /uav/raw_air_data, std_msgs/Float32] --> DiffPressureRosToCyphal(DiffPressureRosToCyphal)
DiffPressureRosToCyphal --> aspd_dpres[ aspd.dpres, uavcan.si.sample.pressure.Scalar]

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8. Battery

Cyphal interface:

Interface	Communicator's Port	Message	Rate
Udral/Battery	pub.energy_source pub.battery_status pub.battery_parameters	reg.udral.physics.electricity.SourceTs reg.udral.service.battery.Status reg.udral.service.battery.Parameters	1...100 ~1 ~0.2

ROS-interface:

flowchart LR
battery[ /uav/battery, sensor_msgs/BatteryState] --> BatteryRosToCyphal(BatteryRosToCyphal)
BatteryRosToCyphal --> energy_source[ energy_source, reg.udral.physics.electricity.SourceTs]
BatteryRosToCyphal --> battery_status[ battery_status, reg.udral.service.battery.Status]
BatteryRosToCyphal --> battery_parameters[ battery_parameters, reg.udral.service.battery.Parameters]

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9. Rangefinder

Cyphal interface:

Interface	Communicator's Port	Message	Rate
Rangefinder	pub.range	uavcan.si.sample.length.Scalar

ROS-interface:

flowchart LR
tas[ /uav/height, std_msgs/Float32] --> RangefinderRosToCyphal(RangefinderRosToCyphal)
RangefinderRosToCyphal --> aspd_tas[ aspd.tas, uavcan.si.sample.length.Scalar]

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2. PX4 Cyphal interface

The actual Cyphal interface on the PX4 node configured in VTOL octoplane coaxial can be illustrated with Yukon gui tool:

Here green topics are publishers, red topics are subscribers, gray topics are RPC-services. A few topics disabled topics are not shown to make an image more compact.

1. Actuator

Cyphal interface:

Interface	PX4's Port	Message
udral/actuator	pub.udral.esc.0 pub.udral.readiness.0 sub.udral.feedback.0 ... sub.udral.feedback.7	udral.service.actuator.common.sp.Vector31 reg.udral.service.common.Readiness zubax.telega.CompactFeedback .

Related PX4 parameters:

Name	Description
UCAN1_ESC_PUB	Cyphal ESC publication port ID
UCAN1_READ_PUB	Cyphal ESC readiness publication port ID
UCAN1_FB0_SUB	Cyphal ESC 0 zubax feedback port ID
...	...
UCAN1_FB7_SUB	Cyphal ESC 7 zubax feedback port ID

On PX4 side actuators logic is implemented within UavcanEscController, ReadinessPublisher and UavcanEscFeedbackSubscriber drivers.

2. IMU

Cyphal interface:

Interface	PX4's Port	Message
imu	sub.udral.imu.0 sub.udral.imu.accel.0 sub.udral.imu.gyro.0	uavcan.primitive.array.Real16.1.0 uavcan.si.sample.acceleration.Vector3 uavcan.si.sample.angular_velocity.Vector3

Related PX4 parameters:

Name	Description
UCAN1_IMU_SUB	Udral IMU 0 subscription port ID
UCAN1_ACCEL_SUB	Udral Accelerometer 0 subscription port ID
UCAN1_GYRO_SUB	Udral Gyroscope 0 subscription port ID

On PX4 side IMU logic is implemented within UavcanAccelerometerSubscriber and UavcanGyroscopeSubscriber drivers.

3. Magnetometer

Cyphal interface:

Interface	Communicator's Port	Message
Magnetometer	sub.udral.mag.0	uavcan.si.sample.magnetic_field_strength.Vector3

Related PX4 parameters:

Name	Description
UCAN1_MAG_SUB	Udral Magnetometer 0 subscription port ID

On PX4 side IMU logic is implemented within UavcanMagnetometerSubscriber driver.

4. Barometer

Cyphal interface:

Interface	Communicator's Port	Message
Barometer	sub.baro.pressure.0 sub.baro.temperature.0	uavcan.si.sample.pressure.Scalar uavcan.si.sample.temperature.Scalar

Related PX4 parameters:

Name	Description
UCAN1_BAROP0_SUB	Barometer 0 pressure subscription ID
UCAN1_BAROT0_SUB	Barometer 0 temperature subscription ID

On PX4 side IMU logic is implemented within UavcanBarometerSubscriber driver.

5. GNSS

Cyphal interface:

Interface	Communicator's Port	Message
udral/gnss	sub.gps.point.0 sub.gps.status.0 sub.gps.sats.0 sub.gps.pdop.0	reg.udral.physics.kinematics.geodetic.PointStateVarTs uavcan.primitive.scalar.Integer16 uavcan.primitive.scalar.Integer16 uavcan.primitive.scalar.Integer16

Related PX4 parameters:

Name	Description
UCAN1_GPS0_SUB	GPS 0 subscription port ID
UCAN1_GPSPD0_SUB	GPS 0 pdop subscription port ID
UCAN1_GPSSA0_SUB	GPS 0 sats subscription port ID
UCAN1_GPSST0_SUB	GPS 0 status subscription port ID

On PX4 side GNSS logic is implemented within UavcanGnssSubscriber driver.

6. RGB LED

Cyphal interface:

Interface	Communicator's Port	Message
Udral/rgbled	pub.udral.rgbled.0	reg.udral.physics.optics.HighColor

Related PX4 parameters:

Name	Description
UCAN1_RGBLED_PUB	Cyphal RGB Controller port ID

On PX4 side RGB LED logic is implemented within RGBControllerPublisher driver.

7. Airspeed (including Differential Pressure)

Cyphal interface:

Interface	Communicator's Port	Message
udral/airspeed	sub.udral.aspd.cas.0 sub.udral.aspd.tas.0 sub.udral.aspd.dpres.0 sub.udral.aspd.temperature.0	uavcan.si.sample.velocity.Scalar uavcan.si.sample.velocity.Scalar uavcan.si.sample.pressure.Scalar uavcan.si.sample.temperature.Scalar

Name	Description
UCAN1_ATAS0_SUB	Udral Airspeed TAS 0 subscription port ID
UCAN1_ACAS0_SUB	Udral Airspeed CAS 0 subscription port ID
UCAN1_ATEM0_SUB	Udral Airspeed Temperature 0 subscription port ID

On PX4 side Airspeed logic is implemented within UavcanAirspeedSubscriber driver.

Name	Description
UCAN1_DPRES0_SUB	UDRAL Differential pressure 0 subscription ID
UCAN1_DPRES1_SUB	UDRAL Differential pressure 0 subscription ID

On PX4 side Differential Pressure logic is implemented within UavcanDiffPressureSubscriber driver.

8. Battery

Cyphal interface:

Interface	Communicator's Port	Message	Rate
Udral/Battery	sub.udral.energy_source.0 sub.udral.battery_status.0 sub.udral.battery_parameters.0	reg.udral.physics.electricity.SourceTs reg.udral.service.battery.Status reg.udral.service.battery.Parameters	1...100 ~1 ~0.2

Related PX4 parameters:

Name	Description
UCAN1_BMS_BP_SUB	UDRAL battery paramteters source subscription ID
UCAN1_BMS_BS_SUB	UDRAL battery status source subscription ID
UCAN1_BMS_ESC_SUB	UDRAL battery energy source subscription ID

On PX4 side Battery logic is implemented within UavcanBmsSubscriber driver.

9. Rangefinder

Cyphal interface:

Interface	PX4's Port	Message
Rangefinder	sub.udral.range.0	uavcan.si.sample.length.Scalar

On PX4 side Rangefinder logic is implemented within RangefinderSubscriber driver.

3. Design

The package is designed to support a new type of simulator or autopilot interface just in case.

It has an autopilot interface that is represented with Cyphal HITL at the moment. It supports both PX4 and ArduPilot.

It has ROS (noetic) interface for UAV HITL simulator. It is suitable for PX4 (mainly mainteined) and ArduPilot (not well tested though).

In the main file, the application converts data from one interface to another and vice versa.

The structural relationship between the interfaces is shown in the figure below:

+-------+-------+-------+-------+-------+-------+-------+------+------+
|          Application entry point (src/main.c) .cfile                |
+-------+-------+-------+-------+-------+-------+-------+------+------+
           |                                    |
+------+-------+------+   +------+-------+------+-------+-------+-----+
| Autopilot interface |   |            Simulator interface            |
+------+-------+------+   +------+-------+------+-------+-------+-----+
           |                         |                      |
+------+-------+------+   +------+------+------+   +--------+---------+
|     Cyphal HITL     |   |   ROS interface    |   |    AP_JSON       |
| autopilot interface |   | UAV HITL simulator |   |     Gazebo       |
| (PX4 and ArduPilot) |   |  (PX4/ArduPilot)   |   | (ArduPilot only) |
+------+-------+------+   +------+------+------+   +--------+---------+

AP_JSON interface is not supported at the moment.

It is considered to migrate on ROS 2 later, so a new simulator interface may appear.

4. Redundancy

Cyphal/CAN communication allows to provide a few options of redundancy implementation.

Firstly, it allows multiple instances of sensors to be used. While the number of UART/I2C sensors connected to an autopilot is limited by the number of physical connectors on the autopilot, you are free to use multiple sensors on the CAN-bus: 2 GNSS sensors, 2 airspeed sensors, multiple rangefinders and navigation lights distributed around the vehicle and controlled by the autopilot - these are perfectly fine.

At the moment, the cyphal communicator and the custom branch of PX4-Autopilot supports 2 airspeed (differential pressure) sensors to demonstate this possibility and test it. You are free to extend it by adding an additional subject.

Secondly, redundancy can be provided by designing an UAV with more motors than the minimum required for flight. If one motor fails, the remaining motors can compensate for the loss of thrust, allowing the vehicle to maintain stability and control. One common approach is to build a hexacopter (six motors) or an octocopter (eight motors) instead of a quadcopter (four motors). With additional motors, the quadcopter can continue to fly even if one or more motors fail.

At the moment, Cyphal communicator as well as Cyphal/UDRAL are limited by 31 motors, though this number can be increased by using an additional control group or extending UDRAL specification. PX4 are limited by 16 motors, that is enough for most of the applications.

As an example, HITL simulator supports octocopter airframe to demostrate this possibility.

Thirdly, the redundancy can be provided by using an additional physical interface (transport layer). It can be second or third CAN-bus, or even another interface such as Cyphal/Serial or Cyphal/UDP.

The cyphal communicator allows to use multiple interfaces. By default it is based on vitual CAN-interface with name slcan0. You can specify another number of the interface and run an additional instance. PX4 capabilities are based on the specific hardware, but modern versions of the hardware typically have 2 CAN-buses.

5. Installation

Before running the communicator, you need to do 3 things:

1. Create virtual CAN. It is expected that you are using CAN-sniffer device such as UAVCAN sniffer and programmer. An example of script that creates SLCAN is scripts/create_slcan.sh. This script automatically detect a connected device and create slcan0 port. You should create virtual CAN once after each sniffer connection to your PC.
2. Configure environment variables. This step is required for setting subjects port id and few pathes. As an example, you can run source scripts/config.sh. You should call this script in each shell session.

After these steps you are able to run the communicator.

6. Running

You should connect a CAN-sniffer to an autopilot as shown below:

You should create slcan0.

Then run the communicator using the launch file:

roslaunch cyphal_communicator cyphal_communicator.launch

7. Usage example

Below you can see an example of using the cyphal_communicator in conjunction with a VTOL dynamics simulator.

8. LICENSE

The Cyphal Communicator project is licensed under the GNU General Public License, version 3