drag=(k1*accAccumX)+(k2*(accAccumX*accAccumX));
grandVelX=accAccumX*(-drag);
[SOLVED] Physics 2D drag problem
Author
Hi, I'm having difficulties with drag.
My coefficients are set to:
k1=.5
k2=.5
My equation to integrate the drag looks like this:
Ah, I made that error once too :-) I assume that accAccumX is either a vector or the vertical part of a vector - in other words it can have both negative and positive value! The trouble lies here: (accAccumX*accAccumX) since + * + and - * - is always positive, your drag will work in the same direction no matter how the body moves. All you need to do is say (accAccumX*abs(accAccumX)), making sure one of the terms is always positive. Then your drag will work in the opposite way of the body's movement.
Cheers,
Mike
Cheers,
Mike
Author
I'm starting to get the feeling that setting a maximum velocity as a result of drag isn't going to be simple.
Author
Whoops, didn't see your answer. I think that might do it!
PS. you've been a lot of help :D
PS. you've been a lot of help :D
Author
By Jove, I think I've got it! Since it's a force I need to add it not multiply it to the acceleration.
The correct code looks like this:
k1=.09;
k2=.01;
drag=(k1*accAccumX)+(k2*(accAccumX*Math.abs(accAccumX)));
accAccumX+=(-drag);
grandVelX=accAccumX;
Again, thanks! I would have still been stuck on direction otherwise.
James
The correct code looks like this:
k1=.09;
k2=.01;
drag=(k1*accAccumX)+(k2*(accAccumX*Math.abs(accAccumX)));
accAccumX+=(-drag);
grandVelX=accAccumX;
Again, thanks! I would have still been stuck on direction otherwise.
James
Glad you got it working. That math.abs() thing had me ripping my hair out too :-)
Here's what my drag equation looks like. It works on force-level and only depends on an air friction coefficient, particle area, and particle velocity squared.
Cheers,
Mike
Here's what my drag equation looks like. It works on force-level and only depends on an air friction coefficient, particle area, and particle velocity squared.
Force += -AirFriction*Area*Velocity*Abs(Velocity)Cheers,
Mike
Quote:Original post by NotTheCommonDose
I'm starting to get the feeling that setting a maximum velocity as a result of drag isn't going to be simple.
It's not simple but not too hard either:
Write the equations of motion:
F = a - k*v;
v = integral(F)
=>
a - k*v = dv/dt;
Or as a diff equation:
dv/(a - kv) = k*dt
Thus you get v = vmax*(1 - exp(-k*t))
You want v ~= vmax (equal to some degree) => 0.99vmax = vmax(1-exp(-k*t)) for some t you want: Solve for k to get the constant that will give you a certain maximum velocity, reached within the required time.
From here
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