hi when i run these codes, it says empty point, waht is problem?

Code:
 #include <acknex.h> 
#include <default.c>

ENTITY* carbody;
ENTITY* tireleft;


var joinbody;



action mybody()
{
	carbody=me;

    phent_settype (my, PH_RIGID, PH_BOX); 
    phent_setmass (my, 70, PH_BOX); 
    phent_setgroup (my, 2);
    phent_setfriction (my, 20); 
    phent_setdamping (my, 40, 40); 
    phent_setelasticity (my, 50, 20); 

}

action lefttire()
{
	
tireleft=me;
		
	phent_settype (my, PH_RIGID, PH_SPHERE);
	phent_setmass (my, 10, PH_SPHERE);
	phent_setgroup (my, 2);
	phent_setfriction (my, 60);
	phent_setdamping (my, 40, 40);
	phent_setelasticity (my, 50, 20);
    
   joinbody= phcon_add( PH_WHEEL, carbody, my); 
    phcon_setparams1 (joinbody, my.x, vector(0, 0, 1), vector(1, 0, 0)); 
    	phcon_setparams2 (joinbody, vector(-30, 30, 0), nullvector, vector(50000, 100, 0));
}


void main()
{
	
	level_load("test.wmb");
wait(4);
	ph_setgravity (vector(0, 0, -386));

		
	
		while(1)
	{
		if(key_w == 0 & key_s == 0 & key_a == 0 & key_d == 0)
		{
			phcon_setmotor(joinbody, vector(0,50,0), nullvector, nullvector);
		
		}
	

if(key_a == 1&key_d == 0)
		{
			phcon_setmotor(joinbody, vector(-100,50,0), vector(0,0,0), nullvector);

		
		}
		
		wait(1);
}
		
}



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