SixDOFConstraint: support mLimitsSpringSettings for rotations

[zkrx]

I am applying a SixDOFConstraint to my bodies in order to limit the extent of the rotation among the X and Z axis. I would also like for my bodies to come back to their original rotation (0°) automatically with the help of a spring.

Unfortunately, mLimitsSpringSettings is not supported for rotations on 6DOF, only translations:

When enabled, this makes the limits soft. When the constraint exceeds the limits, a spring force will pull it back. Only soft translation limits are supported, soft rotation limits are not currently supported. 

Are there any plans for supporting this? Or how can I work around this? I tried using a HingeConstraint. I could have exactly what I want one axis at a time, but not on both axis at the same time (or the body gets overconstrained and won't rotate anymore). I also tried using a SwingTwistConstraint, but it does not appear to support soft limits at all.

Cheers!

[jrouwe]

The best way to achieve this is to use a motor. Supply the spring frequency and damping to the MotorSettings object associated with the X and Z axis. Activate the motor with SetMotorState. Drive it to your 0 degree target using SetTargetOrientationCS.

[zkrx]

Thank you for the advice. I managed to implement what I want with a SixDOFConstraint and its associated Motor. When I advance the helicopter, it tilts 20° forward. Same when I move backwards or sideways. It comes back to neutral when I stop. I can freely rotate around Y (yaw) as well.

It runs fine. Here the helicopter starts with an identity rotation:
https://github.com/user-attachments/assets/85c1251b-24ef-47ef-a148-09bdac8f2155

But I start having issues when I want to limit the X or Z rotation axis (with SetLimitedAxis). More precisely when crossing a yaw rotation of 180° around the Y axis. When the helicopter is perfectly flat, I can rotate past the 180° point freely. When the helicopter has a small tilt (X) or roll (Z) angle, then I have hiccups or even cannot cross the 180° point:
https://github.com/user-attachments/assets/ca00e58b-cf01-427c-8c95-141c013efcdc

Could this be a problem within the limits code or am I just doing something silly?

I am using SetTargetOrientationBS to tilt around X and Z, SetTargetAngularVelocityCS to rotate around Y.

Code:

BodyCreationSettings creation_settings(new SphereShape(sphere_radius),
				    position,
				    rotation,
				    EMotionType::Dynamic,
				    layer);

creation_settings.mOverrideMassProperties = EOverrideMassProperties::CalculateInertia;
creation_settings.mMassPropertiesOverride.mMass = 10000;
creation_settings.mLinearDamping = 10.0f;
creation_settings.mAngularDamping = 10.0f;

Body *body = body_interface.CreateBody(creation_settings);

BodyCreationSettings creation_settings2(new SphereShape(0.001f),
				       body->GetPosition(),
				       body->GetRotation(),
				       EMotionType::Dynamic,
				       Layers::IGNORE);
creation_settings2.mAllowedDOFs = EAllowedDOFs::TranslationX | EAllowedDOFs::TranslationY | EAllowedDOFs::TranslationZ;
Body *base = body_interface.CreateBody(creation_settings2);
body_interface.AddBody(base->GetID(), EActivation::Activate);

SixDOFConstraintSettings settings;

settings.SetLimitedAxis(SixDOFConstraintSettings::EAxis::RotationX, DegreesToRadians(-80.0f), DegreesToRadians(80.0f)); // <------ this line creates the issue

settings.mMotorSettings[SixDOFConstraintSettings::EAxis::RotationX] = MotorSettings(1.0f, 0.5f);
settings.mMotorSettings[SixDOFConstraintSettings::EAxis::RotationY] = MotorSettings(1.0f, 0.5f);
settings.mMotorSettings[SixDOFConstraintSettings::EAxis::RotationZ] = MotorSettings(1.0f, 0.5f);

SixDOFConstraint *constraint = static_cast<SixDOFConstraint *>(settings.Create(*base, *body));
constraint->SetMotorState(SixDOFConstraintSettings::EAxis::RotationX, EMotorState::Position);
constraint->SetMotorState(SixDOFConstraintSettings::EAxis::RotationY, EMotorState::Velocity);
constraint->SetMotorState(SixDOFConstraintSettings::EAxis::RotationZ, EMotorState::Position);
constraint->SetTargetOrientationBS(Quat::sIdentity());

physics_system.AddConstraint(constraint);