ok you cant use c_move

At the moment I try with phent_fuction like phent_centralforce and it works so far.
The following is my test script for a movement with physics:
#include <acknex.h>
#include <default.c>
////////////////////////////
VECTOR speed1;
function main()
{
level_load ("Physik.wmb");
wait(2);
ph_setgravity (vector (0, 0, -386));
camera.x = 50;
}
action model()
{
phent_settype (my, PH_RIGID, PH_BOX);
phent_setdamping (my, 80, 80);
while(1)
{
//speed up!//
if (key_i && (speed1.x < 50 && (speed1.x >= 0)))//speed up forwards, if speed1 is 0 or higher
speed1.x += 0.02;
if (key_k && (speed1.x > -10 && (speed1.x <= 0)))//speed up backward, if speed1 is lower than 0
speed1.x -= 0.02;
//break!//
if (key_i && (speed1.x < 0))//break, if speed1 is lower 0
speed1.x += 0.04;
if (key_k && (speed1.x > 0))//break, if speed1 is higher than 0
speed1.x -= 0.04;
if (!key_i && !key_k) speed1.x = 0;
phent_addcentralforce (my, speed1);
//phcon_setmotor//ph_setautodisable//ph_autodisable//ii
wait(1);
}
}