Rotation issues, Gimbal Lock and quaternions in flight mechanics (C++)

[IdoShtivi]

Hi!

I am using UE 5.4.3 and C++.

I am working on a small spaceship project and while working on the flight mechanics I ran into some issues with making the spaceship rotate properly.

My spaceship is a pawn with FloatingMovement component (btw I am not sure if this is the proper way to do it, just felt kinda straight forward). I set up the Enhanced Input system with a steer action that is a Vector2D.
I have a very simple plan for the start: with the WSAD keys held down, the spaceship’s pitch and yaw should update and the spaceship should rotate up / down and to the sides accordingly.

At first I’ve done it with Rotators but very soon I ran into the Gimbal Lock issue when attempting to make a full 360 steer and figured out I should switch to quaternions.
This is how the function that handles input from the user look like:

void APlayerSpaceship::handleSteerInput(const FInputActionValue& value)
{
	const auto input = value.Get<FVector2D>();
 	const auto deltaRot = FRotator(input.Y, input.X, 0).Quaternion();
 	AddActorLocalRotation(deltaRot);
}

I’m curerntly having the following issue:
If I steer at one direction only, everything worksfine. However if I combine sidewise and upwise steering at the same time, instead of just having the pitch and yaw updated, the roll is being changed too.

I attached a video for reference, you can see the rotation values at the top left.

Any idea what makes this happen?

Thanks!

[moke]

The first issue is not a gimbal lock problem; it’s possible that the rotation of other components in your pawn is causing this phenomenon. I wasn’t able to reproduce this issue.

If you want to replicate the gimbal lock problem, you can write the following code:

void APlayerSpaceship::handleSteerInput(const FInputActionValue& value)
{
    const auto input = value.Get<FVector2D>();
    const auto deltaRot = FRotator(input.Y, input.X, 0) + GetActorRotation();
    SetActorRotation(deltaRot);
}

As for the second issue, the change in roll is normal. Due to the gimbal lock problem, Euler angles cannot be simply added together; instead, transformations should be applied using matrices to ensure the rotation matches the visual effect. If you want to learn more, you can look up information related to Euler angles.

[IdoShtivi]

Actually the code snippet that you posted is what I had initially.
The thing is that now I switched to using quaternions instead of Euler angles which did solve the gimbal lock issue. I just don’t understand what causes the roll problem.

[IdoShtivi]

Finally found the solution here:

Prevent rotation around certain axis with Quaternion

This code now fixed my issues:

void APlayerSpaceship::handleSteerInput(const FInputActionValue& value)
{
	const auto input = value.Get<FVector2D>();
	
	const auto currentQuat = GetActorQuat();
	const auto currentRotation = GetActorRotation();
	const auto newQuat =
		FRotator(0, input.X * steeringSpeed, 0).Quaternion() *
		currentQuat *
		FRotator(input.Y * steeringSpeed, 0, 0).Quaternion();

	SetActorRotation(newQuat);
}```