Fix FW transition throttle glitch for tilting rotor quadplanes #29696

priseborough · 2025-04-04T22:09:45Z

This is a fix for the instant forward motor(s) throttle drop that can occur when a quadplane with tilting rotors completes the transition from VTOL to FW flight. This issue was reported here #28957

This fix:

Extends the functionality of the set_throttle_min function such that the rate that the lower limit releases can be controlled by a TECS_THR_ERATE parameter and the throttle out previous value used by the TECS throttle rate limiter can also be optionally reset. If TECS_THR_ERATE is <=0 the legacy behaviour will be observed, ie the minimum throttle will be held for one TECS frame after the function is called.

Adds a function to the motors library that enables the raw normalised throttle demand to be obtained for a specified motor index.

Adds a function to the SRV_Channels library that enables the slew rate limiter state to be set for a specified channel function.

Adds a function to the tiltrotor class that provides the mean throttle of all tilting motors.

When the transition into FW flight is ready to complete it checks for a throttle demand from tilting rotors or if not available the forward motor throttle demand. The TECS minimum throttle and SRV_Channels forward throttle are both set to this value.

Testing on a multirotor VTOL with forrward tilting motors shows that the TECS throttle lower limit is set and releases at the specified 0.2 rate.

Here's a before and after for a SITL test using the -v Plane -f quadplane-tilthvec option

Before - the throttles of the tilting motors step to 0 before increasing

After - the throttles of the tilting motors ramp down smoothly

Decay the lower limit to -1 with the rate controlled by a user adjustable parameter. Allow the set_throttle_min function to reset the the output slew rate limiter.

…nishes When quadplane FW transition finishes, get the throttle of the motors used for forwrd flight and reset the TECS minimum throttle ramp and the servo channel slew limiter to prevent a sudden drop in motor throttle that upset the vehicle.

…le limits" This reverts commit b9f7238.

priseborough · 2025-04-06T22:23:58Z

@tridge - I need help with setting up compiler directives to manage flash space

libraries/AP_TECS/AP_TECS.cpp

tridge

thanks for this @priseborough !

ArduPlane/tiltrotor.cpp

libraries/AP_TECS/AP_TECS.cpp

tridge · 2025-04-07T22:32:44Z

@priseborough also please note this PR which allows the existing throttle slew limit to apply to tilted motors:
#28960
we may want both mechanisms. The advantage of the other PR is it works for non-TECS modes

priseborough · 2025-04-08T10:22:53Z

@priseborough also please note this PR which allows the existing throttle slew limit to apply to tilted motors: #28960 we may want both mechanisms. The advantage of the other PR is it works for non-TECS modes

I think we need both. That PR deals with issues before transition completes, this one with what was happening immediately after for tiltrotor setups. Note that the reset of servo throttle channel slew limiters should also help for non TECS modes after transition completes.

IamPete1

This looks good. #29011 Would handle the smoothing of the throttle outputs. But you would still need to workout the average throttle for the TECS re-set.

libraries/SRV_Channel/SRV_Channel_aux.cpp

IamPete1 · 2025-04-08T20:32:19Z

libraries/AP_TECS/AP_TECS.cpp

-    // 31 previously used by TECS_LAND_PTRIM
+    // 31 previously used by AP_Int8 TECS_LAND_PTRIM which was removed in November 2022
+
+    // @Param: THR_ERATE


Do we need a new param? Can't we use the existing plane throttle slew limit?

It needs to be slower based on flight testing where the tilting rotors were energising the front wing in a tandem wing configuration.

OK, should we default to 0 meaning use the existing slew limit? Or at least we should use the larger of this and the existing slew limit. Someone may have set a very slow slew limit already.

ArduPlane/tiltrotor.cpp

This reverts commit 34c0595.

priseborough · 2025-04-11T11:49:33Z

In the process of cleaning it up and updating in response to review comments a single frame glitch in the servo demands has been introduced. I'll remove the needs rework flag when the cause of this has been resolved.

This prevents a single frame glitch in throttle that can result if the TECS throttle is fetched before the next TECS update.

priseborough · 2025-04-13T04:31:10Z

The reason for the glitch in servo demand after incorporating review comments was af73ffb

The current throttle state also has to be reset to avoid a glitch if the TECS throttle demand is fetched before the next TECS update cycle.

I've added a patch that adds the set of current throttle state.

priseborough · 2025-04-13T04:36:26Z

@IamPete1 and @tridge using the conversion form thrust to throttle applied to thrust demand is not exactly the same as retrieving the raw throttle demand.

If I revert commits 3ad8f32 and 8d227d9 I get the following ESC demands for vectoring quad SITL test

Using the thrust to throttle scaling I get a small dip at the time of the reset, indicating that motors->thr_lin.thrust_to_actuator does not produce the same result as motors->get_raw_motor_throttle.

I worked out why this was happening. The motors library throttle to thrust and vice-versa transformations operate with throttle in the range from spin min to spin max. Plane does not do this so the throttle returned by thr_lin.thrust_to_actuator needed to be mapped to the range from spin min to spin max. Doing this removed the throttle glitch.

priseborough · 2025-04-23T07:16:40Z

@tridge and@IamPete1 I've tagged it for the next dev call.

priseborough · 2025-04-24T07:38:09Z

It has been flight tested on a ARACE tiltrotor at commit 1204cba

Here are a couple of the forward transitions from the flight:

Transition in AUTO - no sudden dips in forward throttle on completion

Transition from QLOITER to CRUISE - no sudden dips in forward throttle on completion

IamPete1 · 2025-04-25T18:10:30Z

ArduPlane/quadplane.cpp

+            // and set the throttle channel slew rate limiter to prevent a sudden drop in throttle
+            plane.TECS_controller.set_throttle_min(throttle, true);
+            SRV_Channels::set_slew_last_scaled_output(SRV_Channel::k_throttle, throttle);
+            SRV_Channels::set_output_scaled(SRV_Channel::k_throttle, throttle);


I think we also need to do the same for k_throttleLeft and k_throttleRight.

IamPete1 · 2025-04-25T18:11:55Z

ArduPlane/quadplane.cpp

+            SRV_Channels::set_slew_last_scaled_output(SRV_Channel::k_throttle, throttle);
+            SRV_Channels::set_output_scaled(SRV_Channel::k_throttle, throttle);


k_throttleLeft and k_throttleRight again. Might be worth making a helper function.

IamPete1 · 2025-04-25T18:13:28Z

ArduPlane/tiltrotor.cpp

+// throttle of forward flight motors including any tilting motors
+bool Tiltrotor::get_forward_throttle(float &throttle) const
+{
+    if (!_is_vectored) {


Suggested change

if (!_is_vectored) {

if (!enabled() || !_is_vectored) {

IamPete1 · 2025-04-25T18:13:50Z

ArduPlane/quadplane.cpp

+            if (!plane.quadplane.tiltrotor.get_forward_throttle(throttle)) {
+                throttle = 0.01f * SRV_Channels::get_output_scaled(SRV_Channel::k_throttle);
+            }
+            // Reset the TECS minimum throttle to match throttle of forward thrust motors


Should we be doing this reset for none tiltrotors?

IamPete1 · 2025-04-25T18:15:14Z

ArduPlane/tiltrotor.cpp

+    for (uint8_t i = 0; i < AP_MOTORS_MAX_NUM_MOTORS; ++i) {
+        if (is_motor_tilting(i)) {
+            float thrust;
+            const float throttle_range = motors->thr_lin.get_spin_max() - motors->thr_lin.get_spin_min();


This could go outside the loop.

And early return false for !is_positive(throttle_range)

IamPete1 · 2025-04-25T18:20:22Z

ArduPlane/tiltrotor.cpp

+            if (motors->get_thrust(i, thrust) && is_positive(throttle_range)) {
+                throttle_sum += (motors->thr_lin.thrust_to_actuator(thrust) - motors->thr_lin.get_spin_min()) / throttle_range;


Maybe that function to get the actuator output would be better, get_thrust is removing the thrust linearisation and then you have to put it back again here. You could also calculate it from the PWM output using PWM min and max.

Sorry if I gave bad advice on this previously.

IamPete1 · 2025-04-25T18:22:19Z

libraries/AP_TECS/AP_TECS.cpp

-    // 31 previously used by TECS_LAND_PTRIM
+    // 31 previously used by AP_Int8 TECS_LAND_PTRIM which was removed in November 2022
+
+    // @Param: THR_ERATE


OK, should we default to 0 meaning use the existing slew limit? Or at least we should use the larger of this and the existing slew limit. Someone may have set a very slow slew limit already.

IamPete1 · 2025-04-25T18:27:35Z

ArduPlane/quadplane.cpp

            transition_state = TRANSITION_DONE;
            in_forced_transition = false;
            transition_start_ms = 0;
            transition_low_airspeed_ms = 0;
+            float throttle;
+            if (!plane.quadplane.tiltrotor.get_forward_throttle(throttle)) {
+                throttle = 0.01f * SRV_Channels::get_output_scaled(SRV_Channel::k_throttle);


The 0.01 here looks incorrect? The scaled output is 0 to 100, so that makes it 0 to 1, but then it is directly set back to the output on 1614, so it would be 100 times too small?

IamPete1 · 2025-04-25T18:27:54Z

ArduPlane/quadplane.cpp

@@ -1478,6 +1478,15 @@ void SLT_Transition::update()
    // the tilt will decrease rapidly)
    if (quadplane.tiltrotor.fully_fwd() && transition_state != TRANSITION_AIRSPEED_WAIT) {
        if (transition_state == TRANSITION_TIMER) {
+            float throttle;
+            if (!plane.quadplane.tiltrotor.get_forward_throttle(throttle)) {
+                throttle = 0.01f * (float)plane.aparm.throttle_cruise;


0.01 and then setting it back on 1489.

priseborough requested a review from IamPete1 April 6, 2025 21:17

priseborough added 7 commits April 7, 2025 08:19

SRV_Channel: Add function to reset slew rate limiter state

38d3d60

AP_Motors: Add function to get raw motor throttle

34c0595

AP_TECS: Rework the external setting of throttle lower limit

cd153ae

Decay the lower limit to -1 with the rate controlled by a user adjustable parameter. Allow the set_throttle_min function to reset the the output slew rate limiter.

Plane: Add accessor function for tiltrotor equivalent forward throttle

59c54d2

AP_TECS: Add debug logging of external upper and lower throttle limits

493e881

Revert "AP_TECS: Add debug logging of external upper and lower thrott…

47a8d89

…le limits" This reverts commit b9f7238.

priseborough force-pushed the pr-plane-tilt-throttle-fix branch from 15f9261 to 47a8d89 Compare April 6, 2025 22:20

priseborough mentioned this pull request Apr 6, 2025

Plane: quadplane tilt rate issues #28957

Open

priseborough self-assigned this Apr 6, 2025

priseborough added Plane VTOL-Plane labels Apr 6, 2025

priseborough requested a review from tridge April 6, 2025 22:25

Georacer suggested changes Apr 7, 2025

View reviewed changes

libraries/AP_TECS/AP_TECS.cpp Outdated Show resolved Hide resolved

tridge requested changes Apr 7, 2025

View reviewed changes

ArduPlane/tiltrotor.cpp Outdated Show resolved Hide resolved

libraries/AP_TECS/AP_TECS.cpp Show resolved Hide resolved

priseborough added 2 commits April 8, 2025 19:57

AP_TECS: reset _last_throttle_dem for rate limiter state

af73ffb

AP_TECS: Add comment indicating previous use of a parameter slot

095121d

IamPete1 reviewed Apr 8, 2025

View reviewed changes

priseborough added 3 commits April 11, 2025 19:40

Plane: non functional change from review comment

876e77e

Revert "AP_Motors: Add function to get raw motor throttle"

3ad8f32

This reverts commit 34c0595.

Plane: Use inverse throttle map instead of call to raw motor throttle

8d227d9

priseborough force-pushed the pr-plane-tilt-throttle-fix branch from c991bd9 to 8d227d9 Compare April 11, 2025 10:48

priseborough added the NeedRework label Apr 11, 2025

AP_TECS: Reset current throttle when setting minimum value

e3ccf62

This prevents a single frame glitch in throttle that can result if the TECS throttle is fetched before the next TECS update.

priseborough removed the NeedRework label Apr 13, 2025

Plane: Take spin min and max into account when converting thrust to thr

1204cba

priseborough added DevCallEU DevCallTopic and removed DevCallEU labels Apr 23, 2025

IamPete1 reviewed Apr 25, 2025

View reviewed changes

tridge added the SpringValley label Apr 26, 2025

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Fix FW transition throttle glitch for tilting rotor quadplanes #29696

Fix FW transition throttle glitch for tilting rotor quadplanes #29696

priseborough commented Apr 4, 2025 •

edited

Loading

priseborough commented Apr 6, 2025

tridge left a comment

tridge commented Apr 7, 2025 •

edited

Loading

priseborough commented Apr 8, 2025

IamPete1 left a comment

IamPete1 Apr 8, 2025

priseborough Apr 11, 2025

IamPete1 Apr 25, 2025

priseborough commented Apr 11, 2025 •

edited

Loading

priseborough commented Apr 13, 2025

priseborough commented Apr 13, 2025 •

edited

Loading

priseborough commented Apr 23, 2025

priseborough commented Apr 24, 2025

IamPete1 Apr 25, 2025

IamPete1 Apr 25, 2025

IamPete1 Apr 25, 2025

IamPete1 Apr 25, 2025

IamPete1 Apr 25, 2025

IamPete1 Apr 25, 2025

IamPete1 Apr 25, 2025

IamPete1 Apr 25, 2025

IamPete1 Apr 25, 2025

IamPete1 Apr 25, 2025

		SRV_Channels::set_slew_last_scaled_output(SRV_Channel::k_throttle, throttle);
		SRV_Channels::set_output_scaled(SRV_Channel::k_throttle, throttle);

		if (motors->get_thrust(i, thrust) && is_positive(throttle_range)) {
		throttle_sum += (motors->thr_lin.thrust_to_actuator(thrust) - motors->thr_lin.get_spin_min()) / throttle_range;

Fix FW transition throttle glitch for tilting rotor quadplanes #29696

Are you sure you want to change the base?

Fix FW transition throttle glitch for tilting rotor quadplanes #29696

Conversation

priseborough commented Apr 4, 2025 • edited Loading

priseborough commented Apr 6, 2025

tridge left a comment

Choose a reason for hiding this comment

tridge commented Apr 7, 2025 • edited Loading

priseborough commented Apr 8, 2025

IamPete1 left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

priseborough commented Apr 11, 2025 • edited Loading

priseborough commented Apr 13, 2025

priseborough commented Apr 13, 2025 • edited Loading

priseborough commented Apr 23, 2025

priseborough commented Apr 24, 2025

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

priseborough commented Apr 4, 2025 •

edited

Loading

tridge commented Apr 7, 2025 •

edited

Loading

priseborough commented Apr 11, 2025 •

edited

Loading

priseborough commented Apr 13, 2025 •

edited

Loading