How to change PWM output signal?

[maitham]

I'm trying to change the PWM output using dronecode sdk. I don't need to run a mission or anything, I want to do a static test where I can simply change values. I seem to be running out of options in terms of simply changing pwm outputs within a script in a reliable manner (NSH pwm test works but only for main out). Is there anyway of currently doing this?

[hamishwillee]

I don't think this is possible with the SDK because there is AFAIK no API to support it AND this won't necessarily be supported by default in PX4.

Without having tried this (i.e. maybe not correct) .... to make it work in PX4 you'd have to look at adding a mixer file to map control inputs to outputs - http://dev.px4.io/en/concept/mixing.html
To drive it you would need to send the appropriate MAVLink message (or have an onboard app that does the work for you).

[hamishwillee]

PS The people who might help with this are possibly at Interdrone.

@bkueng Can you comment about PX4 support? As I understand it the mixer is what defines what comes out of the MAIN/AUX outputs - for certain inputs (control group UORB topics?). Does the mapping between MAVLink and those UORB topics exist - ie if you create a mixer and send the appropriate MAVLink message will this work?

[julianoes]

@MaithaM1 this will need some work for the SDK.

In the meantime, if pwm test works, you should try to make pwm test work for the aux output as well. Note that there is a -d argument which should enable you to choose the device, e.g. /dev/pwm_output0 or /dev/pwm_output1.

[julianoes]

There is now the set_actuator call:

MAVSDK/src/mavsdk/plugins/action/include/plugins/action/action.h

Lines 447 to 456 in 68c8041

	/**
	* @brief Send command to set the value of an actuator.
	*
	* Note that the index of the actuator starts at 1 and that the value goes from -1 to 1.
	*
	* This function is blocking. See 'set_actuator_async' for the non-blocking counterpart.
	*
	* @return Result of request.
	*/
	Result set_actuator(int32_t index, float value) const;