Simple xpresso rig problem, continues switching between 270 and -90 degrees


Hi all,

I’m having a problem with a very simple car rig I build. I wanted to add a faux banking system to it. But now the car keeps flipping on a certain part of the track.

I’ve included a link to the file to show the problem.

I have the ‘Car’ being aligned to spline, where the axis is on the rear axis of the car. But looking at the target ‘Steer’ with a target tag. I think this part is causing the flipping somewhere. But how and why I don’t get. I tried playing around with rail splines and up vectors and with priority orders, but to no avail.

Would be great if someone could educate/show me where the problem is.



I have no idea why this happens but I “fixed” it by adding a Clamp node to the Body rotation between the Degree Output and the Body Global Rotation nodes.
Min = 0; Max= 0.2
Hope it helps, really curious how to avoid this from happening at all.


Thanks Nanome for this workaround!

Indeed, still curious how this happens.


Actually still not really working, because it keeps on wobbling on the part of the spline where the problem occurs. Because it will keep varying between 0 and 0.2, while it should be 0 there.


Try this - I didn’t understand what the fracture was doing, so I took it out of the equation (that isn’t the fix), but I moved stuff around and it don’t flip anymore.


Thanks for taking a look at it Jed!

It seems that because you separated the AlignToSpline and the Target tag, it now works correct! I had them on the same null. You have the Target tag on the child null. So probably they interfered with each other.

Thanks :slight_smile:


Didn’t have time to debug it, but in xpresso you are using Global Rotations a lot.
There is no such thing as global rotations really, and their values are not reliable as orientation values. You should better be using the vectors to read orientation values.
If you remove the end input of the Global Rotation B it shouldn’t flip like that, and a replacement setup could be made in its place.


Thanks Simon! Not a lot experience with vectors, but will give it a try