Added new configuration parameter UAVCAN_ESC_IDLT.

This parameter, when enabled, enforces that the UAVCAN ESC driver never outputs zero throttle
while the system is armed. This feature is disabled by default, so the change will not break
the experience of current users.

src/modules/uavcan/actuators/esc.cpp

@@ -39,6 +39,7 @@
 
 #include "esc.hpp"
 #include <systemlib/err.h>
+#include <algorithm>
 
 
 #define MOTOR_BIT(x) (1<<(x))
@@ -110,20 +111,14 @@ void UavcanEscController::update_outputs(float *outputs, unsigned num_outputs)
 	uavcan::equipment::esc::RawCommand msg;
 
 	static const int cmd_max = uavcan::equipment::esc::RawCommand::FieldTypes::cmd::RawValueType::max();
+	const float cmd_min = _run_at_idle_throttle_when_armed ? 1.0F : 0.0F;
 
 	for (unsigned i = 0; i < num_outputs; i++) {
 		if (_armed_mask & MOTOR_BIT(i)) {
 			float scaled = (outputs[i] + 1.0F) * 0.5F * cmd_max;
 
-			// trim negative values back to 0. Previously
-			// we set this to 0.1, which meant motors kept
-			// spinning when armed, but that should be a
-			// policy decision for a specific vehicle
-			// type, as it is not appropriate for all
-			// types of vehicles (eg. fixed wing).
-			if (scaled < 0.0F) {
-				scaled = 0.0F;
-			}
+			// trim negative values back to minimum
+			scaled = std::max(cmd_min, scaled);
 
 			if (scaled > cmd_max) {
 				scaled = cmd_max;

src/modules/uavcan/actuators/esc.hpp

@@ -64,6 +64,8 @@ public:
 	void arm_all_escs(bool arm);
 	void arm_single_esc(int num, bool arm);
 
+	void enable_idle_throttle_when_armed(bool value) { _run_at_idle_throttle_when_armed = value; }
+
 private:
 	/**
 	 * ESC status message reception will be reported via this callback.
@@ -88,6 +90,7 @@ private:
 	TimerCbBinder;
 
 	bool		_armed = false;
+	bool		_run_at_idle_throttle_when_armed = false;
 	esc_status_s	_esc_status = {};
 	orb_advert_t	_esc_status_pub = nullptr;
 

src/modules/uavcan/uavcan_main.cpp

@@ -660,6 +660,12 @@ int UavcanNode::init(uavcan::NodeID node_id)
 		return ret;
 	}
 
+	{
+		std::int32_t idle_throttle_when_armed = 0;
+		(void) param_get(param_find("UAVCAN_ESC_IDLT"), &idle_throttle_when_armed);
+		_esc_controller.enable_idle_throttle_when_armed(idle_throttle_when_armed > 0);
+	}
+
 	ret = _hardpoint_controller.init();
 
 	if (ret < 0) {

src/modules/uavcan/uavcan_params.c

@@ -76,3 +76,12 @@ PARAM_DEFINE_INT32(UAVCAN_NODE_ID, 1);
  * @group UAVCAN
  */
 PARAM_DEFINE_INT32(UAVCAN_BITRATE, 1000000);
+
+/**
+ * UAVCAN ESC will spin at idle throttle when armed, even if the mixer outputs zero setpoints.
+ *
+ * @min 0
+ * @max 1
+ * @group UAVCAN
+ */
+PARAM_DEFINE_INT32(UAVCAN_ESC_IDLT, 0);