Nested Attributes not Working in Form

[yellowreign]

I have a form that uses two models - badge and badge winners. The user_id and community_id fields are needed for badge_winners which is nested in badges.  I was trying to learn from Ryan Bates' Railscast (http://railscasts.com/episodes/196-nested-model-form-part-1)

The error I'm getting is: 

ActiveRecord::UnknownAttributeError in BadgesController#create

unknown attribute: user_id

app/controllers/badges_controller.rb:42:in `new'

LIne 42 corresponds to this line in :create

@badge = Badge.new(params[:badge])

here's the controller:

  def new

    @badge = Badge.new

    badge_winner = @badge.badge_winners.build

    respond_with(@badge)

  end

  def create

    @badge = Badge.new(params[:badge])

    if @badge.save

      flash[:notice] = "Badge was successfully created."

      redirect_to home_path

    else

      flash[:notice] = "There was a problem creating your badge."

      redirect_to home_path

    end     

  end

Here's the form (both community_id and user_id are populating fine):

<%= form_for(@badge) do |f| %>

    <%= f.label :Description %>

    <%= f.text_area :description %>

    <%= f.fields_for :badge_winners do |builder| %>

         <%= builder.hidden_field :user_id ,:value => user_id %>

         <%= builder.hidden_field :community_id ,:value => community_id %>

    <% end %>

    <%= f.submit "Give Badge" %>

<% end %>

The models (user_id and community_id are fields in the BadgeWinner table):

  class Badge < ActiveRecord::Base

     belongs_to :community

     has_many :badge_winners, :dependent=>:destroy

     accepts_nested_attributes_for :badge_winners

  end

  class BadgeWinner < ActiveRecord::Base

    belongs_to :user

    belongs_to :badge

  end

I'm hoping someone's able to help.  I just know it's a newbie error somewhere.  Thanks in advance for any assistance!