sry for taking this thread, but my problem is akin.
I write the code, that Ryu posted and use it for my physics.

temp.x = -1000;
temp.y = 0;
if(key_w == 1) { temp.x = camera.pan; }
if(key_s == 1) { temp.x = camera.pan + 180; }
if(key_a == 1) { temp.x = camera.pan + 90; }
if(key_d == 1) { temp.x = camera.pan - 90; }
if(temp.x != -1000) { temp.y = 15 * time_step; }
ball_speed.x = fcos(temp.x,temp.y);
ball_speed.y = fsin(temp.x,temp.y);
ball_speed.z = 0;
phent_addcentralforce(ball, ball_speed);

But the Ball don't move...
What I writed wrong?

The code is in the while of the main function.

I use A7 Commercial