- Manual/Aum/AU ???

ball_force.x = 200 * time_step * (key_cur | key_d - key_cul | key_a);
ball_force.y = 200 * time_step * (key_cuu | key_w - key_cud | key_s);

==

ball_force.x = 200 * time_step * (clamp(key_cur+key_d,0,1)-clamp(key_cul+key_a,0,1));
ball_force.x = 200 * time_step * (clamp(key_cuu+key_w,0,1)-clamp(key_cud+key_s,0,1));