jack_length=0;
	jack_inc=[22];
	while(jack_inc!=0)
		{
		jack_inc=jack_inc/2;
		move jack1b to y-axis 0 - (jack_length + jack_inc) now;
		if(get GROUND_HEIGHT(get PIECE_XZ(jack1b))<get PIECE_Y(jack1b))
			{
			jack_length=jack_length + jack_inc;
			}
		}
	move jack1b to y-axis 0 now;
	move jack1b to y-axis 0 - jack_length speed JACKS_Y_SPEED;