A Wheeled Vehicle’s wheel meshes will fall off if the vehicle (or more specifically, the root, which would be the vehicle skeletal mesh) is not currently simulating physics, and you decide to Set Simulate Physics to true (while playing / at runtime).
I originally found this problem toying around with a vehicle I made within the 4.8 version of the “Vehicle Advanced” template, but I’ve found this also happens with the vehicle in the 4.9 version of the “Vehicle” template.
Steps to easily see this behavior are as follow:
- Start a new project using the “Vehicle” blueprint template.
- Open the Sedan blueprint.
- Within the main Event Graph, add these nodes:
- Start playing the game. Drive around and toggle the physics. Observe wheel behavior.
I’ve messed around with plenty of settings within the vehicle blueprint itself, the animation blueprint for the vehicle, and the physics asset the skeletal mesh uses. However I wasn’t able to pinpoint what exactly is going on here.
Here are some of the things I’ve tried, and some of the things I’ve noticed:
- The vehicle, when simulating physics, still works completely fine.
- When re-enabling physics, adding on the Set Physics Asset node with the the Force Re Init bool set to true will crash the editor (probably because that doesn’t re initialize the physics asset like I thought it would, but it was worth a try)
- If you are accelerating and/or turning at the moment of re-enabling physics, the wheels will roll off in the direction they are pointing, on what appears to possibly be the spheres used for their collision in the physics asset.
- This is interesting. Open the Sedan blueprint, select the vehicle mesh, and in the details panel search for “No Skeleton Update” which will be under the Skeletal Mesh category. Setting this option to true will prevent the vehicle skeletal mesh from animating, including the wheels (you can see this by turning and noticing the front wheels are not turning). If you drive around and toggle the physics, the wheels won’t fall off. Of course they aren’t animating either.
- The last two observations pretty much leave me stumped. I’m not sure if this is a problem with the physics asset, or the animation blueprint. Maybe both, maybe neither?
Is there any way of fixing this so that when you re-enable physics for the car, the wheels will continue to animate correctly? It would be nice for situations like attaching the vehicle to something in order to transport it somewhere, and then detaching it and allowing it to drive again. Any help with this, especially identifying if this is a bug or not, is much appreciated.