When using lower or more realistic gravity, vehicles using constraints normally hinge constraints or ball and socket constraints commonly runs into problems with bumps that don’t actually exist in real time. This problem happens with both cylindrical and sphere tires, there has not been a found fix with this problem yet.
Examples of the problem:
Expected behavior
The car should drive smoothly on single parts or smooth turns using multiple parts.
Regularly experienced this on my own chassis and game as well. I presume it is a physics solving error related to having several parts overlapping/sudden orientation changes.
Still should be worked on, however.
I also experience this issue quite frequently, and it can be quite annoying and intruding to the process of making cars.
This problem, at least for me, is increasingly frequent and extreme. I could see this being related to microscopic elevation differences in parts? (This has been a problem with Roblox as well, for example: large race tracks will have parts shift out of nowhere when you play the game - creating a sometimes large difference)
This definitely needs to be worked on.
This has been a long-living bug that is and has been super annoying and happens super bad with flat terrain. Regardless of if the terrain bumpiness is another issue, I really hope this gets fixed. A big win for physics stability and reliability
Instead of decreasing gravity does decreasing the Density of the vehicle make a difference?
What’s the Density of your wheels?
Are your suspension mechanism parts similar densities? If they aren’t then Roblox physics can have issues with the joints.
I have a track at my Suspension Test game that allows me to drive my F1 car at about 233 studs per second in the straight sections and I haven’t noticed this issue (although it does in the banked corners which were very roughly constructed, but I haven’t actually tested in in a long time).
Density of any part of the vehicle makes no difference unless you make it astronomically heavy - in which case the vehicle handles more like a container ship than a car and isn’t even worth the effort.
If you decrease density, the violence of the bumps increases and can even flip you.
Additionally, there are few, if any, of these issues on straights. It’s mostly on corners, flat or banked. if you’re turning, you’re probably going to see it at one point or another.
I can attest to this being a common issue, especially during turns that require many parts. It seems like in the intersection where parts collide with each other – although there is no discernable gap – the wheels of the car will collide anyway due to some fault of how the Roblox physics engine works. This effect can be tested by making a road up of very short parts. Unioning a group of parts and setting the collision method to “Box” has fixed this for me but with the downside of inaccurate collisions.
I’ve never had issues with Density when I make the wheels the most dense part of the vehicle and make the Mass of the chassis/car fairly low. It helped me get higher traction without the ‘container ship’ feel.
I did a test with 2048 stud long x 128 wide parts, set up in a 4096 stud square (so 2 Parts x 32 Parts in the square) and definitely noticed the same issue.
Pretty sure it’s close to what @Crimson_Insel mentioned, but it isn’t the microscopic Y elevation, it’s the Orientation of long Parts getting offset by 1/100ths of a degree when floating point error causes them to be different between building in Studio and testing/playing.
(Yes! You can actually enter .0001 stud increments in the Position Property of the Part (or .001 degrees in the Orientation) and see a difference when you hit enter while watching at the edges of Parts.)
the question is, what makes you think your wheels are perfectly round?
In our cases, the collision hit box is a cylinder or a ball (more likely, and is what I have as well).
That would definitely explain it. I have seen stuff like that on large race tracks, particularly on straights made of multiple parts!
Thanks for the explanation. I do think Roblox can take a look at that and experiment with how to remove that error, to try and solve this problem.
To add onto said point, they are the roundest things we have readily available with accurate collision.
Along with that, this glitch mostly occurs when turning, not when travelling in a straight line - which leads me to believe it is the track, and not necessarily the cars (this glitch happens with Tank Chassis, custom Hinge Chassis, and even A-Chassis).
If you look at the 3rd clip its only one part that is in contact with the tires and there is bumps
Hi RealDevPerfect,
I’d like to take a look at this problem. Can you provide me a repro place with either or both cars and one of the tracks you use?
Thanks
Here are two examples; one with multiple parts and another with terrain
terrain_bounce_repro.rbxl (53.4 KB)
multipart_bounce_repro.rbxl (54.3 KB)
the problem goes away once you change cylinder wheels to the ones with a flat surface, meaning the cause of the effect is indeed the approximation of the cylinder’s surface (seemingly ignored by the collision solver)
therefore, either use high-poly cylindrical meshes for your wheels modelled in Blender, or make a full suspension model as shown in the Racing template, where each of the wheels has its motor and a damping system
also notice, there is indeed some degree of randomness both in collision solver and center of mass calculation - it allows objects to fall and distribute more naturally each time they collide with surfaces; otherwise, all movements would have become strictly deterministic, and various unstable systems became either stuck or looping infinitely (such as a rolling coin which never loses momentum, for example)