AI models running at random speeds

My models are too run in a straight line. some faster and some slower, if thers a way to make this happen guidance would be appreciated.

Thanks

F.e. use define, like:
define speed,skill1;

then in action
my.speed = random(10);
c_move(me, vector(my.speed *time_step,0,0), nullvector, ignore_passable | glide);