ArcadeVehiclePhysics 0.1V

Made by Ben McInnes Email: hello[at]benmcinnes.com Twitter: @BSMcInnes

A repo for creating an arcade-inspired physics system for vehicles in Unity.

The repo use and test case is a car, but the scripts could be used for other vehicle types as well. The scripts involved in the project could be used for several types of vehicles if need be but the use and test case has been that of a car.

This is a side project and, while I have a lot of ideas on how to improve this, I'll be coming back to it when I have some free time. If you have any feedback or thoughts, please contact me via email or on twitter.

If you use this repo, I would love to see what you make!

Information

This project was built and tested for use with a controller. In the interest of keeping the dependencies light, I have used Unity's default Input manager.

I would highly recommend Sinput by Sophie Houlden

Credits

The awesome Muscle Car model was created by Asuza

Dependencies

ArcadeVehiclePhysics.package

• Unity Cinemachine
• PostProcessing Stack

NOTE: You may need to upgrade your version of Cinemachine depending on the version of Unity you are using.

Sample Scene

• TextMeshPro
• Probuilder - For Level geometry

Unity Version

This project was built and tested in Unity 2018.4.5f1 LTS Once the project is further along, it will be tested in different versions in order to make sure there are no issues. Contact me at [email protected] if you run into any issues.

References

The following talks have influenced my approach to vehicle physics:

• It IS Rocket Science! The Physics of Rocket League Detailed
• Supercharged! Vehicle Physics in 'Skylanders'
• The Science of Off-Roading: 'Uncharted 4's' 4x4

Components

The implementation has been broken up into small, single responsibility scripts. This way you can pick and choose what you are interested in using. I hope this more modular approach will allow designers to build a larger variety of vehicle types.

Car Physics (CP)

For the best results (but please consider the performance costs) it is advised to change the Unity default physics settings to the following:

Physics (Edit -> Project Settings -> Physics) Default Solver Iterations: 12 Default Solver Velocity Iterations: 12

Time (Edit -> Project Settings -> Time) Fixed Timestep = 0.01666667 (60Hz)

CpMain

This is the main hub for the state and data about the vehicle. All the other components reference and update it.

CpInput

Gets the acceleration and steeting inputs from the player. Abilities check for their own inputs which is not ideal but it is done for simplicity.

TODO:

1. Make sure that all inputs are handled from within CpInput. Abilities should register themselves to CpInput when added to the vehicle and deregister when removed.

CpAcceleration

This script contains two approaches to applying acceleration to the vehicle, and also calculates the speed data of the vehicle. You're welcome to use whichever approach best suits your workflow or project.

The first approach scales of the applied force, depending on the current velocity of the vehicle. This is simpler to implement, but less intuitive to design for unless you are well aquainted with physics.

The second approach uses a Velocity-Time curve to calculate what force should be applied. This is more complicated to calculate, but far more designer friendly. The goal of this project is to be more design-centric, so I prefer this approach. It is outlined in the Skylanders GDC talk mentioned above, but here are the steps:

The Process works using reverse evaluation of the given Velocity-Time AnimationCurve.

1. Binary search using current forward speed to find the time value on the graph.
2. Add one time step onto that time value and evaluate the graph to get the new velocity.
3. Calculate a = (Vf - Vi)/deltaTime
4. Return the new force to apply (Must use ForceMode.Acceleration to ignore mass)

The designer only has to create a Vel-Time graph which outlines the behaviour they want out of the vehicle, eg. they can set the Animation Curve to go from 0 - 100km in 5 seconds and that is exactly how it will respond.

NOTE: To be able to reverse it has to be factored into the Velocity-Time graph.

CpTurning

Turning is implemented by applying a Torque to the Rigidbody around the Y-Axis. The torque is applied using Forcemode.VelocityChange so that angular velocity is affected directly, and the mass is ignored.

A speed factor is applied to the turning force so that the vehicle cannot turn at full force if it is standing still. An offset can be added to this speed factor to adjust how quickly the max turn force is achieved.

TODO:

1. Use an AnimationCurve to scale torque so that the designer has more visual control.
2. Test implementation of the Vel-Force curve mentioned in the CP_Acceleration component

CpColliderData

Uses the colliders of the vehicle to determine the average normal of the surface the vehicle is on.

This is useful for:

• applying angular stability forces.
• checking if the vehicle is on the ground but not on its wheels.

CpDrag

Adjusts the drag and angular drag of the vehicles rigidbody. The drag values can easily be adjusted depending on various scenarios.

NOTE: The collider physics material used has no friction and so currently, drag is the force that slows the vehicle down.

CpLateralFriction

Implemented based on understanding of the Rocket League Talk.

Lateral friction is how much the tyres will slip sideways. This implementation is simple and aims to give the player good control while driving, but some skid when it comes to land at an angle. Otherwise it can be quite jarring if the car stops dead.

When grounded, the side speed is calculated and the force required to cancel that movement is applied as an Forcemode.Impulse.

To make the vehicle slide more or less, the designer can adjust the base tyre stickiness.

• 0 - The tyres have no grip
• 1 - The tyres stick perfectly

NOTE: Currently, at very high speeds this functionality does not work correctly.

TODO:

1. Apply surface normal factor to the lateral friction calculations so that the tyres are more slippery on angled surfaces

CpStabilityForces

Implemented based on understanding of the Rocket League Talk.

The player loses some degree of control when the vehicle is airborn or rolling. The stability forces are used to get the vehicle into a controllable state as soon as possible.

"Linear" Stability

• Applied when between 1 and 3 tyres are grounded.
• Applies a downward force from each wheel position.
• Snaps the wheels down to the ground so that the player can be in control again as soon as possible.

"Angular" Stability

• Only applied when the vehicle colliders are in contact with the ground but the wheels aren't grounded
• Calculates the angle between the AverageSurfaceNormal and the Vehicles local up direction
• Applies a roll torque to try to align the car Up with the surface normal to get the car back onto it's wheels.

The angular stability only calculates the roll torque as trying to stabilise multiple axis can be unpredictable. -Rocket League Talk

CpWheels

Keeps a list of the physics wheel transforms. Each wheel raycasts downward in order to get the surface normal and whether the wheel is grounded or not.

At this point in time the height of the physics rig is set by a pair of capsule colliders. This is definitely a weakness in the framework and needs some iteration.

TODO:

1. Experiment with using physics based suspension but need to determine the trade off between control and being able to handle wheel collisions more accurately
2. Look into using Physics.ComputePenetration to handle collisions with sub suspension height objects. Similar to how it is handled in the Unchartered 4x4 talk.

Car Visuals (CV)

While researching various approaches to building vehicle systems, I found that the general consensus is that it is better to seperate the phyiscs rig from that of the visual rig.

Pros

• Less parameter tuning
• More consistent control and more accessible
• Quicker iteration time on visual changes
• Can fake the physics reactions so that most players wouldnt notice

Cons

• Loss of procedural, more reactive animation
• Have to maintain seperate physics and visual rig

CvWheels

Controls where the wheel models are placed and the tire particles

CvBodyMovement

Fakes the effect of momentum/intertia on the car. It rolls the vehicle's body depending on the side speed/steering input and pitches it depending on the accel input and forward speed.

Can easily tweak the amount of angle from the input and speed.

Camera System - Cinemachine-based system

The camera system is quite basic at the moment. There are two virtual cameras, one follows the vehicle from behind while grounded and focuses slightly ahead of where the vehicle is heading. The second follows the player in air, and focuses in the direction of movement. It does not rotate, so that if the vehicle is spinning in the air the camera remains stable and manageable.

Car Abilities (CA)

Now that the Physics and Visual rigs have been discussed (and set up on your side), it is time to give the vehicle some abilities. I mean, it is for a video game after all...

Still experimenting with the best way to implement this, but ideally the abilities should be modular and as self contained as possible. If you have some ideas/feedback on how to better keep this decoupled, please let me know!

CaAirControl

Allows player to turn the vehicle in the air. Implementation is the same as CP_Turning.

CaJump

The force is applied as an Impulse at the center of mass so that the vehicle jumps directly upwards without any rotation. Press the input down to charge the jump to a max force and jump on release.

CaDrift

Allows the vehicle to slide. This is done by reducing the TyreStickiness which decreases the corrective side Impulses in the CP_LateralFiction script. The TyreStickiness is reduced along the DriftCurve set by the designer. The duration in and out of the drift can be set by the designer and this scales the movement up and down the Drift Curve.

To reduce the amount of forward speed lost when coming out of a drift, the corrective side impulse is applied as a forward acceleration.

CaBoost

While boosting an extra forward force is applied to the vehicle. There is a limited amount of time you can boost and it recharges while not boosting.

End Note

This is a work in progress. If you try it out, please let me know if you have any feedback on how I can improve this system. You can contact me at [email protected]