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K_J_M

Member Since 26 Feb 2007
Offline Last Active Nov 06 2013 04:50 PM

Posts I've Made

In Topic: Oldschool retro RPG - feedback and ideas needed

03 December 2012 - 11:05 PM

Hi Acharis.

I downloaded your game and gave it a whirl.

And i really like this. Posted Image

Everything ran smoothly and was really easy to pick up and play without instructions.

The only thing i felt was lacking was the sound effects and possibly some music to help generate some more atmosphere.

I contemplated writing something similar a while ago, more along the lines of the 'Ishar' games but instead decided against the step movement idea.

But it works really well in your game.

I can see this working really well on mobile devices.

Might be worth considering porting it to mobiles when you've finished the PC version.

The graphics have a real old school charm about them.

Keep up the good work.

KJM

In Topic: Car Simulation Headaches Part_#2

13 September 2012 - 04:19 PM

Hi.

For my Autocross Racing game i used lateral Pacejka coeficients similar to this curve.

Posted Image


This gives a very forgiving tire with a lot of grip at all slip angles.

I noticed in your second video that your car reaches a maximum slip angle before it loses grip and spins around.
This is classic of a Pacejka curve that peaks at a small slip angle.
once past this peak, the tire has no grip and the car spins around.
Altering your Pacejka curve so it looks similar to mine above should help prevent this and allow for drifting.

You should be able to get variable car handling from using different curves. The Racer sim for instance uses different coefficients for front and rear tires.

But specifically for my game, i just rotate the cars velocity vector by the lateral Pacejka force to give that arcade drifting feel.

It's not physically accurate in any way and i did have to tune various attributes to get the correct feel i was after.

In theory, a physically accurate sim should be able to produce a wide range of handling for a car from an arcade drift feel to a simulation mode, by altering such things as the Pacejka curves, engine power, gear ratio's ect.

But in practice creating an accurate sim is going take a long time to do (particularly because theres very little information available on the subject), so it comes down to priorities.

If your priorities are to get an arcade game written as quickly as possible then i see no reason in hacking together an arcade sim, which is exactly what i did for my game.

If on the other hand you want to write a physically accurate sim and then use that as a basis for games, then it will take a long time to get right.
You could use a third party car physics engine and i know some general purpose physics engines support wheel physics and suspension constraints (Newton physics engine for example) , so that may be an easier route for you.

In Topic: Car Simulation Headaches Part_#2

13 September 2012 - 11:38 AM

"
I would argue with that. In your post #6, the blue arrow IS the real velocity of the tyre, which is perpendicular to the vector from CG to wheel pos, but not to the wheel's heading.
So it WILL generate both long/lat forces. If you do the same calculations for the remaining 3 wheels the sum of all Fx's will be zero if the CG is at the center of the car, so that's why there is no movement of the car body.
"

Thanks for the explanation Bmarci. Posted Image

I see there were flaws in my understanding.

I was assuming that a stationary car spinning on the spot has zero linear velocities and as a result no slip angles could be generated.

But in fact, you show that although the car chassis has no linear velocites, the wheels actually do and therefore the slip angles can be calculated whilst ignoring the angular velocity of the chassis.

Sorry for any confusion pochypoch.

In Topic: Car Simulation Headaches Part_#2

13 September 2012 - 12:27 AM

Thanks for the comments.

Both Long and Lat Pacejka formulas need FZ (load) as one of the inputs.

And a resulting force as output.

The traction circle caps the forces to a maximum limit. I think the Racer sim reduces Longitude forces in favour of Lateral as a way to cap the forces.

But there are several different methods that i've seen.

Since the traction circle limits forces, and these are calculated from Pacejka which requires FZ (load) as an input, the traction circle caclulations are applied after the forces have been calculated.

In Topic: Car Simulation Headaches Part_#2

12 September 2012 - 03:52 PM

Hi.

The Pacejka formula's work in wheel local coordinates.

Longtitude pointing in the direction the wheel rolls in and Lateral at 90 degrees to Longtitude direction.

So,as i understand it, Case 1 Example is correct.

Although i'm no expert, i always understood that a stationary car spinning on the spot with the steering centred produces no longtitude forces from the tires to move the car forwards or backwards. But only lateral forces to slow down the rate of spin.

But, maybe someone with more detailed knowledge than me can give a more accurate explanation.

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