# Two ways to make Box2D cars

I am showing you two ways to make cars with Box2d, with source codes included

These are examples I found on the web – I will make my ones later – you can find interesting in order to make cars using Box2D.

Top Down Car Simulation

Making a top down game in Box2D is not that different than making a side view game… you just don’t have to set gravity.

Here it is a top-down racing game

And this is the script to handle it

Truck car game

This is a truck car game, this concept was very popular a couple of years ago.

The truck is made using various joints, such as revolute joints and prismatic joints.

Here it is the source code:

• Simple and Perfect! Thanks Emanuele, i search this entire last week!

• Eliott Robson

WOW, Always wanted to know how to do this! How would i go about using images rather than squares so i could design a motorbike or something?

• Pretty neat.

• Awesome, I have an idea for a top-down auto game and had no idea where to start. Thanks!

• Very cool examples! Can’t wait to see some more.

• In the first example the car moves as though in water. The centre of rotation at the car is exposed on the centre? I tried to do such, the truth not with Box2D, and the centre of rotation of the car put between back wheels: http://xitri.com/2008/07/09/flash-programming-drive-a-car.html

• Great post, emanuele!

• Peter

:o :o Awesomeeeeeeeee… I searched for this for a while ago but gave up, now I found it xD

• Hey… why is the y scale -1 in the second example? The values look so small also..

• dVyper

These examples are absolutely amazing! Good work :)

• Hi ,
in the truck game demo you have the add wheel function and you set there wheel1.
the question is how do I reset the wheel1.angle?

If I use wheel1.GetAngle I can only see it but can’t set it and if I try with wheel1.angle=0; or wheel1.rotation=0; doens’t work.. please help
thanks!
you’re awesome!

• Xorox

Hi Emanuel, great example, as always.. i have a question, how would you introduce a handbrake to your topview car simulation ?

• T

great examples! I was wondering if you could make an updated version for the new 2.1a version of Box2d – as it looks like GetXForm (and xforms altogether) are now gone from the library!

• iAN

GetXForm() is replaced by GetTransform() in 2.1a

• Nice tutorial.
But when i copy the source code, i cant run it,
here’s the error I’ve recieve:

1046: Type was not found or was not a compile-time constant: Input.

1180: Call to a possibly undefined method Input.

1120: Access of undefined property FRateLimiter.

I don’t know that input variable.;-(

can any one knows this case?
and what if i want my movieclip to be the image on stage?

• saravanan

Hi guys second tutorial not working how said its awesome

• saravanan

please explain how to use this code pls give zip format help me

• Rodrigo

Hey Emanuele. I’m hacing trouble understanding this code:
spring1.SetMaxMotorForce(30+Math.abs(800*Math.pow(spring1.GetJointTranslation(), 2)));
spring1.SetMotorSpeed((spring1.GetMotorSpeed() – 10 * spring1.GetJointTranslation()) * (5)/Constantes.RATIO);
spring2.SetMaxMotorForce(30+Math.abs(800*Math.pow(spring2.GetJointTranslation(), 2)));
spring2.SetMotorSpeed( -4 * Math.pow(spring2.GetJointTranslation(), 1));

I changed the density of my car and the torque applied to the wheels… and they started dancing all over the place when going to fast. Any ideas?

Rod

• drobs

very nice tutorial, has helped alot, but I also have the same problem as eanjo.
have been looking around the web for a few days now and just can’t find it ..

so if someone could help me out, it would be greatly appreciated.

drobs

• Pingback: Physics Test()

• Rodrigo

I don’t think I’m doing this right. I took the topdown simulation and created a new project on FlashDevelop. It worked like a charm, except for one thing: The car dances all over the place. I mean, really.. I steer left and accelerate, and it goes like right and starts spinning arround the main body’s mass center.

I think the problem is in killOrthogonalVelocity. Any ideas?

• Indy

Hi,

Great tutorial. Any advice on how you would handle allowing the car to skid a little on different frictional surfaces?

Regards

i

• Indy

Hi,

Looking at the side car with 2 wheels, I dont see anything in the code which makes the axles appear as they do. i.e. they appear to be 2 shapes per axel, with one cylinder moving inside another cylinder? All I can see in the code is one rectangle formed as an oriented box – per axle.

Any ideas?

Regards

i

• Mike

I’m getting the same issues as eanjo.

1046: Type was not found or was not a compile-time constant: Input.
1180: Call to a possibly undefined method Input.
1120: Access of undefined property FRateLimiter.

Any body know how to fix this. Thanks!

• Mike

Does any body know what my errors are? (read comment above) I’m in Flash CS5 running Box2d 2.0.2

• Randomman159

I am also getting these errors, and i went through half a dozen different versions of Box2d. The one with the least errors were the Box2d 2.0.*, so basically what you are using. To get rid of the errors i just removed the FRateLimiter line of code, and replaced all the ‘input’ with a class i made, but you could simply have boolean values for whether keys are pressed, and check those booleans (instead of checking through a class).

• vikram

Really Nice Emanuele! Your tutorials are really helpful for the freshers who want to enter into the gaming field. I am a live example for this. Actually I learned a lot from your tutorials. Your tutorials made me win my first interview.

I have a small problem now! I am creating a dirt bike type game. I created the bike and some platforms. I created a bridge. When the bike is moving on the bridge, it just going into the bridge after traveling through 2 links.

• lacas82

How to do this lines in java?:

var sidewaysAxis = targetBody.GetXForm().R.col2.Copy();
sidewaysAxis.Multiply(b2Math.b2Dot(velocity,sidewaysAxis))

Theres is nothing R.col2 in there…

• Pingback: Cocos2d Box2d Car | Applausible Blog()

• Hi great work!

Quick question, in order to synchronize this simulation over network, which variables do I need to send over to my clients? :)

• corporalik

Hi,
please, is there a simplified version of top-down car? this sample is too hard for newbie.

• Pingback: Drakon - place » Box2D bike()

• A great starting point! The side view truck game is great!
There are not a lot of articles on skinning and matching scaling, but I have figured it out.
I have added editable vehicles and track and am working on scoring and sound. Lots of fun.
The prismatic joints sure are finicky and the whole update camera using velocity thing never worked out for me, so I used the location of the vehicle as my offset for all layers. Torque had to be increased to 50 to get over the big hills and make actual jumps and if you put a tall skinny rectangle at each end of the main body rectangle it will not end up on it’s back as much.

• NEVENA ALEKSIEVA

Hi Emanuele, great tutorials, I’m an actionscript developer and I’m doing my masters degree at the moment. We have an asignment (coursework) with the original Box2d engine (written in C++), so I decided to use the second example as part of the coursework, rewrote it from AS3 to C++, used the testbed and it does not look right, axles are not fitting within the cart properly, I could email an snapshot if it will help. Thanks

• NEVENA ALEKSIEVA

ps – I know it has to do with flash coordinate system being upsidedown, do I then have to scale all graphics.y with -1?
Cheers

• Philippe

Hello Emanuele,
First thanks for all the good work.
I just posted an updated version of the top-down car you had made with version 2 on the box2d forum,
the car does not move!
I guess I just forgot something essential, but I don’t see what?
Would you please have a try.
(source code is for flashdevelop, should be easy to compile and run),
then please feel free to use it for an update of this post.
(I’m using this to drive a car inside a flat 3d environment).
Thanks,
Philippe

• Philippe

Found solution,
I had forgotten the fact you said that dynamic bodydefs have to be declared as such explicitely, (type=b2Body.b2_dynamicBody).
I have posted the corrected working code on the Box2D forum thread.
Thanks,
Philippe

• Bob

Hello dear friend.I have this mistake;
1046: Type was not found or was not a compile-time constant: Input.

• aitken85

In the update function, what do the numbers represent that are passed into these two methods:

```spring2.SetMaxMotorForce(...); spring2.SetMotorSpeed(...);```

My car must be a lot heavier, as your current values don’t allow my “springs” to push back up. Just wondering if there’s easy way to find out what values I should use instead trial-and-error x1000.

Cheer, Chris.

• Pingback: Couch Multiplayer | Emotely Blog()

• Leo

Great Grat tutorial Emanuele. Stavo cercando di contattarti tramite email ma non funziona il bottone contact.

Ciao

• very interesting, we can rock in flash.

• Hardik

Hello Sir
Thanks for such a good post.
I want the same thing but in cocos2d with box2d.I dont want to use flash.
Can you help me with the same working model

• Silver Moon

Hello

I have few questions , regarding the first example of a car :

1. Why does the car stop moving when up/down button is released. Since ApplyForce is being used , isnt he car supposed to keep moving once its starts moving ?

2. What is keeping the wheels attached to the car. When car gains speed , the wheels dont hang out of the car, how is this being done ?

Regards
Silver

• Sohan

great tutorial,

I have ported this code in iphone,but my wheels are not moving when I accelerate.

if I remove the lines

(Spring1)->SetMaxMotorForce( );
(Spring1)->SetMotorSpeed();

(Spring2)->SetMaxMotorForce( );
(Spring2)->SetMotorSpeed();

it works,but not as smooth as it runs here,can you tell me where I am going wrong and what are actually these parameters effects.

• Dhivakar

Hi Emananuel,

Ur work here is amazing, in the second example the truck goes upside down when i cross the obstacles. do u have any idea how to have a truck or a car in 2D side scrolling game which doesn’t go upside down when it cross an obstacle?

• thanks, very useful tutorial :)

• Eliya

Emanuel

My work web security is warning me that your site contains malicious code. This happened on my blog as well, you should check your site to make sure you haven’t been hacked, and install a security plugin.

• Davina

Hi Emananuel,

I’m having a problem… What box2d version is this tutorial using? Because the version I am using doesn’t have b2XForm… What’s the alternative in the newer version?

Thank you.

• Shekhar Suman

Does anybody know what does this line do…

var sidewaysAxis = targetBody.GetXForm().R.col2.Copy();

btw Great Tutorial.

• Jrog

The side-view vehicle code appears to be copied in its entirety from a 2008 post on the Box2D forum entitled “box lying on cycle jitters”:
http://www.box2d.org/forum/viewtopic.php?f=8&t=1669

There’s nothing wrong with building on the work of others, but simply copying and neglecting to give credit is poor form.

• PDM

Hi emmanuele,

I’m using Box2d 2.1a and I made a side view car using techniques in this post.
Everything looks fine, but when it comes to applying torque to the car some problems occur.

* it takes too long to start spinning and when it spins , can’t stop.
(there is no setMassFromShapes() function in Box2D 2.1a, I wonder whether this could be the problem)

* when I use the world.clearForces() the car doesn’t spin at all.

• vkreal

PDM,

Did you figure out your issue?

• Tyler

Do you think a game like this is possible with Stencyl ?

• PDM

No vkreal, couldn’t find a solution.

• PDM

It seems too much inertia.

• Marius

Hi,
i want to make a sideviewed racing game in javascript and canvas. your second tutorial is basically what i want to do but in javascript. it would be an nice base for me so what do i have to do to convert your actionscript in javascript to use it with box2dweb? im not familiar with actionscript. my main problem is the typecast at spring1. Hope you can help me.

PS: Sorry for my bad English.

• Vaughan

Thanks so much, superb example and exactly what we’re after…in Nape though. Do you have any recommendations of how to do this using Nape – have tried everything but can’t quite map this example to its joints. Or perhaps you might do a Nape example sometime :)

• Wow, I’ll have to add Box2d to some of my games! I’m impressed with how much you can achieve with so little code.

• Pingback: Box2d c++ can't see b2PolygonShape | DL-UAT()

• Nancy

So, your tutorials are great. One thing I absolutely stuck on. I am blown away by how I can’t figure this out.

I made a structure that looks like an equal sign. Two bodies, exact same size with a single prismatic joint that pushes up the top one, like a spring. The top body floats above it, but i cannot, for the life of me, figure out how to narrow the distance between the objects. There is no ‘length’ parameter for prismatic joint.

I tried positioning the top body lower in space. (it just gets pushed up)
I tried making it weigh more. (it just increases in density until it breaks through the ground)
I tried changing the settings on the prismatic joint, translation, angles, limits, everything.