VHDL robot design not working

To make LED connect to RD_LED, just assign it outside of a process. Or if you want to make it a variable, just assign LED above if counter = 50000 then.., and asign RD_led (as a variable) where it is now. Variables can store values between clocks if you put things in the right order.

For DC, because it is set a value and nothing else, Quartus will probably just assume it is a constant. But making it a generic might be a good idea. Generics are created like ports, in the generic section:

entity my_ent is
  generic (
    DC    : integer;
  );
  port (
  );
end entity my_ent;

Then when you do the instantiation, you give it a value.

my_inst : entity work.my_ent
generic map (
  DC => 32678,
)
port map (
...
);

Inside your entity, you just treat generics like constants.