I may be over simplifying this, but while you may think you have a variable in another controller, that may not be true.
When an request comes in and is routed to a controller, an instance of the controller is created. If that other controller is not some how instantiated as part of the request then that variable you think is there is not really there.
Models however do exist (at least in database form). So Basically I think you should be trying to get that @project
variable created in your project_updates
controller by extracting some data from your model.
How do you create the @project
variable in the other controller? Most likely you would use the same approach in this controller to create it, then it would be available to your view.