DShot minimum throttle output

Safranek42 · August 18, 2020, 12:32pm

Hi,

I have noticed that using dshot esc the motor is spinning even when the throttle input is zero.
In QGroundControl at the MAVLINK Inspector servo3_raw parameter was always at least 1, even without throttle command. In the code I have found in src/modules/drivers/dshot/dshot.cpp that when setting minimal inputs, it is set as DISARMED_VALUE + 1 . What is the reason of the +1 (e.g. avoiding division by zero)?

The links to the lines where it is added:

github.com

PX4/Firmware/blob/e9e9556130763aa91f593c3f2ef4bbcfa511c8e9/src/drivers/dshot/dshot.cpp#L253



char DShotOutput::_telemetry_device[] {};
px4::atomic_bool DShotOutput::_request_telemetry_init{false};

DShotOutput::DShotOutput() :
	CDev("/dev/dshot"),
	OutputModuleInterface(MODULE_NAME, px4::wq_configurations::hp_default),
	_cycle_perf(perf_alloc(PC_ELAPSED, MODULE_NAME": cycle"))
{
	_mixing_output.setAllDisarmedValues(DISARMED_VALUE);
	_mixing_output.setAllMinValues(DISARMED_VALUE + 1);
	_mixing_output.setAllMaxValues(DSHOT_MAX_THROTTLE);

}

DShotOutput::~DShotOutput()
{
	/* make sure outputs are off */
	up_dshot_arm(false);

	/* clean up the alternate device node */

github.com

PX4/Firmware/blob/e9e9556130763aa91f593c3f2ef4bbcfa511c8e9/src/drivers/dshot/dshot.cpp#L818



void DShotOutput::update_params()
{
	parameter_update_s pupdate;
	_param_sub.update(&pupdate);

	updateParams();

	// we use a minimum value of 1, since 0 is for disarmed
	_mixing_output.setAllMinValues(math::constrain((int)(_param_dshot_min.get() * (float)DSHOT_MAX_THROTTLE),
				       DISARMED_VALUE + 1, DSHOT_MAX_THROTTLE));
}


int
DShotOutput::ioctl(file *filp, int cmd, unsigned long arg)
{
	int ret;

	/* try it as a Capture ioctl next */
	ret = capture_ioctl(filp, cmd, arg);