PX4 PWM Output

Configure PWM outputs for servo motors and ESC control

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Libraries:
UAV Toolbox Support Package for PX4 Autopilots / PX4 Utility Blocks

Description

The PX4 PWM Output block helps you to configure the PWM output from the PX4 flight controller board. The block accepts time value (in microseconds) that represents the ON period of PWM signal for a particular channel, and passes the same to the corresponding PWM channels on the board.

The PX4 PWM Output block also accepts signals for arming the flight controller and enabling failsafe conditions.

Note

A limitation is observed when the PX4 PWM Output block is deployed on the Pixhawk 1 board and if you select Use default startup script (rcS) as the startup script option for the PX4 Autopilot during the Select System Startup Script in PX4 step of the Hardware Setup process. Then, if you use rcS as the startup script for Pixhawk 1, the PWM block will not work. This limitation is not present for Pixhawk 2.1 (Cube), Pixracer, and Pixhawk 4 boards. The PWM block works after deployment on these Autopilots even when rcS is used as the startup script.

During Connected I/O simulation, this block writes data to the peripherals of the hardware.

Examples

Getting Started with PWM Blocks for PX4 Autopilots

Use the PX4 PWM Output block to generate signals on the PWM pins of a Pixhawk Series controller, and verify the PWM values.

Open Model

Ports

Input

Arm — Arm the PX4 flight controller

0 (default) | 1

Enable signal for arming the PX4 flight controller.

Data Types: Boolean

Set failsafe — Enforce failsafe for PX4 flight controller

0 (default) | 1

Enforce failsafe values even though the failsafe conditions might or might not have occurred. You can specify the failsafe values in the Configuration Parameters dialog box in Simulink.

Note

If you are using PX4 firmware 1.12.3, the value at Set failsafe input port is not valid if you use AUX channels for PWM.

Data Types: Boolean

Ch x — Inputs that accept PWM ON values

0 (default) | 1

Connect the Ch x inputs to signals that represent PWM ON values (in microseconds)

Dependencies

The required Ch inputs are selected using the PWM Channels parameter.

Data Types: uint16

Output

Port_1 — Error status while processing PWM commands

0 (default) | 16-bit value

Obtain the error status of the PWM operations in the block. The error status corresponds to a 16-bit representation of the various possible errors.

An output value of 0 indicates a successful PWM operation (no errors). A non-zero output indicates the different errors that you can interpret based on the 16-bit value.

To interpret the errors (if any), connect the Port_1 output to a Display block that has the Format value set as binary (Stored Integer), and run the model in External mode.

Port_1 (error status) connected to a Display block and viewed in External mode

Use the following table to interpret the 16-bit error status as obtained from the output of PX4 PWM Output block:

LSB of the 16-bit field that is set to 1 (as it will appear in a Display block in case of errors)	Error
1	Failed to open the PWM device (Main/AUX)
2	Failed to obtain the number of servo motors
3	Failed to Arm the PWM device
4	Failed to Disarm the PWM device
5	Failed to set the PWM frequency
6	Failed to select the PWM channel that is configured as input
7	Failed to set the failsafe values on the selected channels (values that are defined in the Main PWM or AUX PWM panes in the Configuration Parameters dialog box)
8	Failed to set the disarmed values on the selected channels (values that are defined in the Main PWM or AUX PWM panes in the Configuration Parameters dialog box)
9	Failed to interpret the Set failsafe input
10	Failed to interpret the Force terminate failsafe mode input
11	Failed to set the PWM motor values
12	Failed to reset the PWM motor values
13	Failed to close the PWM device (Main/AUX)
For example: If the 16-bit error status shows [0000 0000 0010 0000], the bit 6 is set, and the error is that the block failed to select PWM channel that is configured as input. The possible reason can be that you did not select all the channels that belong to a particular group. If the 16-bit error status shows [0000 0100 0010 0000], the bits 6 and 11 are set. The errors are that the block failed to select the PWM channel that is configured as input, and it also failed to set the PWM motor values.

Dependencies

This output appears only if you have selected the Output error status parameter.

Data Types: uint16

Parameters

Main tab

Select PWM Device — Channel category to identify the channels that you are going to select

Main (default) | Aux

Select the category (Main or AUX) to identify and select the corresponding channels. After you select this category, you can select the channels in the parameter list, for Main and AUX, separately.

PWM Channels — Channels to which you want to send the PWM ON time values

Channel numbers

Select the channels to which you want to send the values for PWM ON time (the channels to which you connect servo motors or ESC). The Ch inputs to the block appear based on the selection in this parameter list.

Note

Ensure that you select all the channels that belong to the same channel group. If you need to connect to PWM channels that are in different groups, select all channels in all the desired groups. Only one PX4 PWM Output block per channel category (Main or AUX) is allowed in the entire Simulink model.

Tip

To identify the channel groups in the Pixhawk Series flight controller board, use QGroundControl application on your host computer:

1. Open QGroundControl.

2. Connect the Pixhawk Series flight controller board to the USB port of the host computer.

3. In QGroundControl, go to Mavlink Console, and do the following:

   • To identify the Main channels and their groups, enter the command pwm info.

   • To identify the Aux channels and their groups, enter the command pwm info -d /dev/pwm_output1

Advanced tab

Force terminate failsafe mode — Set the failsafe as permanent and non-recoverable

off (default) | on

If this parameter is enabled, and if an actual failsafe condition occurs, the failsafe values are permanently set. In this case, sending a disable signal (0) at the Set failsafe input, will not have any impact.

Note

If you are using PX4 firmware 1.10.2, the enabling of Force terminate failsafe mode parameter is not valid if you use AUX channels for PWM.

Output error status — Enable the error status as the output

off (default)

Enable the error status of the block as the output. This output is a 16-bit binary value that you can interpret to analyze the errors.

Version History

Introduced in R2018b