Hello. There is no article how to configure CruiseControl.rb(ccrb) for Rails 3 with RVM on internet so far. That's pity. Let's fix it.

First, install ccrb (just download and unzip from https://github.com/thoughtworks/cruisecontrol.rb/downloads).
Create new ccrb project named 'your_project'.

Then let's open ~/.cruise/projects/your_project/cruise_config.rb with your favorite editor.
Uncomment next line:

project.build_command = './build_my_app.sh'

Add build_by_app.sh to your rails application so full path should be ~/.cruise/projects/your/project/work/build_by_app.sh. 
This file should contain next lines:

#!/bin/bash
# Load RVM into a shell session *as a function*
if [[ -s "$HOME/.rvm/scripts/rvm" ]] ; then
  # First try to load from a user install
  source "$HOME/.rvm/scripts/rvm"
elif [[ -s "/usr/local/rvm/scripts/rvm" ]] ; then
  # Then try to load from a root install
  source "/usr/local/rvm/scripts/rvm"
else
  printf "ERROR: An RVM installation was not found.\n"

fi

bundle install
bundle exec cucumber

Start ccrb and build.