New WIP Car Chassis - Feedback wanted!

Am I doing something wrong? It wont move, and if I ramp the power up it still wont move until the wheel flys of completely.

Try messing around with the glue’s face values.

I’ve added an ABS system for the brakes, updated the gear ratios, and fiddled with the power and friction. I’ve tried to counter the weird extra friction in the hinges with an extra force, which mostly works but needs a little extra tuning. The cars now do 0-60 in 8 seconds and max out at 120, instead of 0-60 in 2 seconds and max out at 100, which only RallyX cars do.
However the cars don’t have enough torque, tractions fine, to get up anything other than a shallow hill. I’m thinking it’s because I’m treating my cars as full size but the default roblox gravity is for cars measured in cm not m?

@NWSpacek @Fractality_alt
Did some tests and cylinders are definitely not real cylinders: At about 120MPH cylinder wheeled cars will start to jump around uncontrollably, but using ball wheels results in a perfectly smooth ride at all speeds.


that’s problematic. would you mind filing a bug report?

I’m guessing its intended behaviour though: It’s as NWSpaceK said, it’s a prism and not a cylinder.

I’ve switched to a sphere wheeled car, but this introduces a new problem: As the wheels tilt with the chassis in turning, the part of the sphere in contact with the road changes, and the radius of the rotation of the wheel effectively becomes smaller. This slows the wheels on one side and speeds the wheels on the other, making the car enter uncontrollable turns when using soft and high suspensions.

Are the wheel axis allowed to change relative to the chassis? If they aren’t, I don’t see how it would asymmetrically change the diameter of the wheels because the radius change would be the same as long as the car is not pitching up or down. You can control how the diameter changes as the car rolls by angling the wheels in and out as well as changing how the axis changes as the suspension deflects with various types of linkages.

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Actually that’s a good point all wheels should tilt by the same amount, maybe it’s just a CoM issue.

Looks like the 6th gear is used to save gas at high speeds, but otherwise has no power advantage

Correct we only deal with rigid bodies in Roblox at the moment. So contact patch has no influence on the friction force

I’m curious which primitive are you using for wheel? Cylinder or sphere?

Both of those are modeled as perfect round in our collision system. But the solver allows some margin of error to maintain the collision with the ground


Yes we have angular damping hard coded in our engine. We are working at exposing this in an API, but i can’t promise anything yet.

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Yup that’s the angular damping from our physics engine… I can tell you exactly the equation we are using:

correctedAngularVel = exp( -0.911328 * deltaTime ) * angularVel

Pretty standard for a physics engine to do this. It imitates air friction. But now that we can have stable mechanism with high angular velocities, this can have a major impact.


That graph was with a cylinder. Spheres produced a straight line iirc.

This is very interesting. This means that even though cylinders are implemented as perfectly round, they have more instabilities than spheres. It’s possible it is due to the fact the contact points are jumping between left and right side of the wheel.

So PGS doesn’t have a concept of line contacts as far as cylinders are concerned? That might explain it.

These are all point contacts.

But depending on the cylinder being inclined slightly left or right, the contact point will wander one way or the other. This might cause the instabilities we are seeing in your graph.

Enable “AreContactPointsShown” in Physics settings, you’ll see the contact point jumping around.

We are thinking about reducing this high angular damping. See this thread:

Also we’ve opened up GT3 for testing with reduced damping:

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