Physics Based Truck Game

Cristineltr · September 14, 2015, 9:56am

Hi,

I am trying to make a physics based truck game.

I only have a little experience in 3D modeling with Zmodeler, I used to do mods for GTA IV and Euro Truck Simulator.

The most important thing right now is to get the physics as close to reality as possible. Everything that moves, twists, bends on a real truck needs to do it in my game.

I imported each part of the truck as a static mesh, I created a pawn and I assembled all the parts in UE4 using constraints.

Update

I finally got my truck moving and steering

Also the constraints are much more stable now, almost rock solid

https://youtube.com/watch?v=iaC9eJ0uO2E

I tweaked the truck to get as close as possible to this one https://www.youtube.com/watch?v=jidbxiZc5g4&feature=youtu.be&t=39s

Next I need to make a proper gearbox and differential

Here are 2 videos showing what I hope to achieve

https://youtube.com/watch?v=p7xygByGzY8

https://youtube.com/watch?v=21L7xs2EisQ

anonymous_user_518c3a4c · September 14, 2015, 12:50pm

Hello, Cristineltr.

That looks really good. Rigs of Rods/Spin Tires style, i totally love that. Would you mind sharing some technical details of the implementation?

Cristineltr · September 14, 2015, 2:22pm

I am extremely inexperienced so I might not explain this right.

I started by importing all the parts of my truck, wheels, axels, suspension parts, frame, cabin etc. as static meshes.

After import I double clicked on each static mesh and a window opened where I created collision for it.

I created a pawn, I double clicked on the pawn and a window opened.

I dragged all the parts of the truck in that window and arranged them so that everything was in his place and I checked the Simulate Physics box for each part.

After this I started to add physics constraints and I joined all the parts together.

Cristineltr · September 15, 2015, 5:32am

TooManyfps;378590:

This looks great.

You can move it on its on power by using the attached snippet on each wheel, if your wheels are just imported meshes and connected with constraints in a very raw way.
You turn your wheel(s) to blueprint, then either put the snippet in each of them, or use blueprint communication and reference them all from one blueprint.
What is does is apply a force to the wheel, but not at the center but with an offset from the center, here 25. The force needs to be adjusted to the wheel rotation in case of steering, going uphill etc.
That works really well and gives the most physically accurate driving to date in UE4. It is basically a torque that you apply. Building things like differential lock etc around it means basically testing if wheels are on the ground etc…there can be a lot of stuff done based on the simply snippet, because it is raw stuff and not some vehicle class etc. It is basically the first building stone to making an own vehicle class in blueprints.
Make sure your wheels have high res collision. If it is too low res, the collision mesh will make the wheel hopple at higher speeds.

Thank you,

When I have some time I am going to give this a try.

For the wheels I hope to use Soft Body Physics to simulate realistic tires when this plug-in Tendr: a real-time, volumetric, soft-body physics plug-in for UE4 - Work in Progress - Unreal Engine Forums will be ready.

anonymous_user_e8c998a7 · September 15, 2015, 6:29am

Good luck to you. Hope you will make nice game.

anonymous_user_518c3a4c · September 17, 2015, 9:34am

Thank you for the reply Wheels look really stable, never happened to achieve this by myself…
Mind sharing how you made the suspension? Couldn’t get constraint to behave as a spring…

Cristineltr · September 17, 2015, 11:21am

Here is a picture with my suspension constrains

To make the wheels and the axles more stable I had to increase their mass a lot.

As you can see in the video below they are not 100% stable you can see the rear axle moving when I go over that box at the beginning

From what I understand this is a problem with PhysX: http://forum.unity3d.com/threads/ape-advanced-physics-engine-for-robust-joints-and-powerful-motors.259889/

BoredEngineer · September 17, 2015, 11:25am

Looks great!
How does it behave at high speed?

I did a similar setup for 10 wheeled truck and wheels kept going crazy at high speeds. The only thing that would make them stable is to completely remove their friction. I’ve decided to simulate friction myself but run into a problem of not being able to calculate wheel load because of this bug:

So I’ve ended up with simulating suspension manually as well.

What kind of collision mesh you use for wheels?

BoredEngineer · September 17, 2015, 11:33am

More specifically the problem is that friction is applied to wheel and then propagates through chain of your constraints to the main body. For this to work correctly you need to scale the mass of connected objects in such a way that it’s as close to 1:1 ratio as possible. One way is to fiddle not with mass but with ‘mass scale’ property. Unfortunately this leads to a setup where 30 ton truck has a 3 ton suspension axles connected to 3 ton wheels.

Cristineltr · September 17, 2015, 11:41am

At high speeds the wheels jump like crazy but I hope to use Soft Body Physics to simulate realistic tires when this plug-in Tendr: a real-time, volumetric, soft-body physics plug-in for UE4 - Work in Progress - Unreal Engine Forums will be ready, so for the moment I don’t try to make very high poly collisions for the wheels.

DuncanT · September 17, 2015, 9:48pm

Some sort of tutorial on this sort of thing would be super cool.

Stocker_00 · September 21, 2015, 5:38am

Duncan, there was a project you could download. which had the basics of this, but now it can’t be downloaded. this was the forum page. I downloaded it months back and learn’t how it was done, thanks to the publisher Polyplant all the credit for the tutorial project is to him. I have just uploaded the rar file to my mediafire account so you and others can download it. Also this project is for engine version 4.7

DuncanT · September 21, 2015, 11:47am

Thanks Sean. I remember reading that thread after the first post what it is now (nothing but pictures) so I was a bit confused as to what was going on. I will be downloading that sometime tomorrow, thank you.

Cristineltr · January 21, 2016, 10:56am

Update

I finally got my truck moving and steering

Also the constraints are much more stable now, almost rock solid

I tweaked the truck to get as close as possible to this one Brass Joe T.S., log truck - YouTube

Next I need to make a proper gearbox and differential

BoredEngineer · January 21, 2016, 12:41pm

Very nice! I like how most of the parts are connected to each other instead of being single solid body. The wheels are turning a little to fast, are you using SetAngularTarget of constraint for steering?
Btw, any tips on getting more stable constraints? From my last experiment with aerosled I got much more stable behavior by adding sockets and adding them to physics constrain parameters.

Cristineltr · January 21, 2016, 3:04pm

All the blueprints that I made were made from watching this 3 Videos Custom Vehicles in Unreal Engine - 2 - Simple Car Using Physics Constraints - YouTube Custom Vehicles in UE4 - 3 - Add A Torque Curve & RPM To Simple Car so it can accelerate - YouTube Custom Physics Vehicles in UE4 - 4 - Setup Rear Suspension On Simple Car - YouTube

I didn’t know how to do any blueprints

Here is how my steering blueprints look like

For the constraint stability one of the most important things were this settings on all the truck parts

And the Constraint Projection Values are set to 0.1 for the Projection Linear Tolerance and 1.0 for Projection Angular Tolerance

Another very important thing is Sub-Stepping. I set 16 steps and Max SubStep Delta Time to 0.016

Initially the Max SubStep Delta Time was set to **0.016667 **which was perfect at 120 FPS but when I dropped the frame rate to **60 FPS **the wheels were getting pushed into the ground and jumping around this problem got fixed by changing the Max SubStep Delta Time to 0.016

BoredEngineer · January 21, 2016, 3:31pm

Interesting, I’ve never tried fiddling with “Should Update Physics Volume” and setting under CCD. Will give it a try.

At first my steering setup was similar to yours, for steering this thing:

But now I’ve changed it a bit. When you enable “limited” on angular constraint, you can call “SetAngularTarget” in degrees for it. The nice thing is that you can change this target in real-time, so when I want to turn right I simply start to slowly increase target yaw degrees and constraint will just hold it in that position. I’ll post screenshot of blueprint when I get home, or you can grab a project from github repo GitHub - BoredEngineer/UE4_Tracked_Vehicles: Custom tracked vehicles for UE4, NOT based on PhysX Vehic, blueprint is called Aerosled.

These are really cool tutorials! Thank you for the link.

BoredEngineer · January 21, 2016, 7:23pm

This is how code looks like:

ProcessSteering() function is called on every Tick event.

Setting on constraints are like this:
https://www.dropbox.com/s/tzfxs0f96ez43g0/ConstraintAngularTargetSteering_Settings.PNG

Cristineltr · January 22, 2016, 6:10am

Thanks, BoredEngineer

I also have a very strange problem when I drive on a diagonal on the map my FPS drops to 1 FPS
I made a picture

The green is the directions where everything is ok no mater the speed and the red is where is the problem

BoredEngineer · January 22, 2016, 9:26am

I’ve never seen such bug before. My guess is that you have a problem with one of the physics settings like “UpdatePhysicsVolume” where it needs to keep recalculating some sort of bounding box, when you drive straight along one of the axis then bounding box keeps it shape. This is just a guess.
Do you have any other blueprint code there except for the steering?