# 5. Cyphal PWM node

This page is about Cyphal related details such as interface, supported features, registers, configuration and usage examples and software versions. For general information please refer to the 1. General page, for hardware related details including wiring examples please refer to the uNode or Mini v2 pages.

# 5.1. Cyphal interface

This node interacts with the following data types:

Common for any node

Type Message
1 pub uavcan.node.Heartbeat (opens new window)
2 RPC-service uavcan.node.GetInfo.Response (opens new window)
3 RPC-service uavcan.node.ExecuteCommand (opens new window)
4 RPC-service uavcan.register.List (opens new window)
5 RPC-service uavcan.register.Access (opens new window)
6 pub (since hardware v3) uavcan.node.port.List (opens new window)


Electronic speed controller (ESC) service

This node supports the Electronic Speed Controller (ESC) service according to the UDRAL standard (see for details) (opens new window). It uses the following subjects:

Type Message Topic name
1 subscriber reg.udral.service.actuator.common.sp/* (opens new window) setpoint
2 subscriber reg.udral.service.common.Readiness.0.1 (opens new window) readiness
3 publisher reg.udral.service.actuator.common.Feedback.0.1 (opens new window) feedback

Circuit status service

Like any other RaccoonLab node, this node also supports the Circuit status service. It uses the following subjects:

Type Message Topic name
1 pub uavcan.si.sample.voltage.Scalar.1.0 5v
2 pub uavcan.si.sample.voltage.Scalar.1.0 vin
3 pub uavcan.si.sample.temperature.Scalar.1.0 dev_temp

Since uNode doesn't have an internal DC-DC, it doesn't provide Vin voltage.

# 5.2. Cyphal Registers

Register name Note Description
0 id reboot required Node ID
1 control_mode reboot required Control mode (opens new window)
2 ttl_ms Time to live (read about CONTROL_TIMEOUT here (opens new window))
3 pwm1_ch Index of setpoint
4 pwm1_min PWM duration when setpoint is min.
5 pwm1_max PWM duration when setpoint is max.
6 pwm1_def PWM duration when setpoint is not present or device is not engaged.
7 uavcan.pub.feedback1.id Port identifier.
8 uavcan.pub.feedback1.type persistent reg.udral.service.actuator.common.Feedback.0.1
9 pwm2_ch Index of setpoint
10 pwm2_min PWM duration when setpoint is min.
11 pwm2_max PWM duration when setpoint is max.
12 pwm2_def PWM duration when setpoint is not present or device is not engaged.
13 uavcan.pub.feedback2.id Port identifier.
14 uavcan.pub.feedback2.type persistent reg.udral.service.actuator.common.Feedback.0.1
15 pwm3_ch Index of setpoint
16 pwm3_min PWM duration when setpoint is min.
17 pwm3_max PWM duration when setpoint is max.
18 pwm3_def PWM duration when setpoint is not present or device is not engaged.
19 uavcan.pub.feedback3.id Port identifier.
20 uavcan.pub.feedback3.type persistent reg.udral.service.actuator.common.Feedback.0.1
21 pwm4_ch Index of setpoint
22 pwm4_min PWM duration when setpoint is min.
23 pwm4_max PWM duration when setpoint is max.
24 pwm4_def PWM duration when setpoint is not present or device is not engaged.
25 uavcan.pub.feedback4.id Port identifier.
26 uavcan.pub.feedback4.type persistent reg.udral.service.actuator.common.Feedback.0.1
27 uavcan.sub.readiness.id reboot required Port identifier
28 uavcan.sub.readiness.type persistent reg.udral.service.common.Readiness.0.1
29 uavcan.sub.setpoint.id reboot required Port identifier
30 uavcan.sub.setpoint.type persistent reg.udral.service.actuator.common.sp.Vector4.0.1
31 uavcan.pub.crct.5v.id Port identifier
32 uavcan.pub.crct.5v.type persistent uavcan.si.sample.voltage.Scalar.1.0
33 uavcan.pub.crct.vin.id Port identifier
34 uavcan.pub.crct.vin.type persistent uavcan.si.sample.voltage.Scalar.1.0
35 uavcan.pub.crct.temp.id Port identifier
36 uavcan.pub.crct.temp.type persistent uavcan.si.sample.temperature.Scalar.1.0
37 name reboot required Node custom name

Since uNode has only 2 channels, pwm3 and pwm4 have no effect.

You can check examples of yaml files with registers for micro node (opens new window) and mini v2 node (opens new window).

# 5.3. Configuration

Before using in the real application, it is necessary to configure the device. It is recommended to use Yakut (opens new window) cli or Yukon (opens new window) gui.

Please note that for safety reasons, a node configuration should only be carried out with unarmed propellers!

Step 1. Connect the device

Connect the node via sniffer to your PC.

An example of the connection is shown below.


Step 2. Configure the environment

Typically you will need to:

  1. Configure all required environment variables
  2. Compile DSDL based on public regulated data types
  3. Create SLCAN based on CAN sniffer

Please refer to Yakut and Yukon documentation to understand how to do it.

Step 3. Monitor the node

Let's say, you have a Cyphal node correctly connected to a CAN sniffer.

The state of the node can be visualized using Yakut. Run y mon to see the node. The possible command output is:


Alternatively, you can use Yukon. An example of monitor is shown below:


Step 4. Ports configuration

The minimum possible application requires the following ports to be configured:

  • readiness,
  • setpoint.

Auxillary ports are:

  • crct.5v,
  • crct.temp,
  • crct.vin,
  • crct.feedback*,

According to the specification (opens new window) the port IDs should be in the range [0, 6143]. Disabled subjects should have port id 65535.

A fully configured application might look like this:


You can subscribe to the topics to verify the result:

5v voltage feedback
yukon_monitor_5v yukon_monitor_feedback

Step 5. Parameters configuration

The following parameters must be configured through the register interface:

  • id,
  • pwm* registers,
  • ttl_ms,

The value of id register must be unique within the network. It must be withing the range [1; 126].

The register value of ttl_ms must be at least twice more than the setpoint period.

Since right now the setpoint type is Vector4, pwm*_ch registers supports values from 0 to 3. Other values will configure the corresponded pwm pin to the default state. For ESC it is preferred to have min values as 1000, max value as 2000 and default as 1000. For servo these values might be anything within the range [1000, 2000]. It is up to up.

You may also want to configure the auxillary parameters:

  • name.

Step 6. Control the node

After the configuration, you are able to send the setpoint to the device to verify that everything it was successful.

In general, you should engage the device by sending readiness command, and then send a setpoint.

Click here to show Yakut usage example

Let's say, you have configured registers.

First terminal session. Configure the Yakut environment variables and start to periodically send the readiness message to engage the device. Try the following script. Specify NODE_ID as your actual node ID.


DATA_TYPE=$(y r $NODE_ID $REGISTER_BASE.type | tr -d '"')
y pub -T 0.1 $PORT_ID:$DATA_TYPE 3

Another terminal session. Configure the Yakut environment variables and start to periodically send the setpoint command. Try the following script. Specify NODE_ID as your actual node ID and VALUE as desired value of setpoint withing range [0.0, 1.0]:


DATA_TYPE=$(y r $NODE_ID $REGISTER_BASE.type | tr -d '"')

# 5.4. Ardupilot integration

Ardupilot doesn't officially support Cyphal (at the time of writing), so it is expected to use the custom cyphal branch of ardupilot (opens new window), since PR is not merged.

1. Port configuration

The following Ardupilot Cyphal registers should have the same port identifiers as GPS:

Port Type
setpoint reg.udral.service.actuator.common.sp/* (opens new window)
readiness reg.udral.service.common.Readiness.0.1 (opens new window)

2. Channels configuration

3. Verification

Ports and channels configuration (opens new window)

# 5.5. PX4 integration

PX4 sends setpoint and readiness with following values:

  • setpoint port ID is uavcan.pub.esc.0.id,
  • readiness port ID is uavcan.pub.esc.0.id + 1.

These port identifiers of the autopilot should be the same as those of the node.

PX4 sends setpoint within the range [0; 8192]. So, you also need to configure control_mode as 1.

# 5.6. Versions

Micro and mini v2 releases:

Version Date SHA Link Description
v1.2 Feb 23, 2023 b4e042b link (opens new window) Add port.List, add hardware version, extend git hash length to 64 bit, few fixes
v1.1.2 Nov 17, 2022 4f393f4 - Add control mode parameter to be compatible with PX4
v1.0.1 Oct 23, 2022 47a71fd link (opens new window) Initial release