how to limit number of character of a post on front page?

Hello ,
I am planning to make a autoblogging website with the help of the plugin WP Robot. I tried WP robot on my local server and it is properly fetching the RSS feeds for me. But problem now is that some of the sites allow me to fetch the full content and which I dont want to appear completely on my front page. I was wondering is there any solution which I can clip my (restrict) the number of characters appearing on my front page. Then after if the user click on read more he/ she will be able to see the full post. Mnually I can add <!–more –> where I need a break. But is it possible to do with some tweaks on my theme for auto-blogging?

Thank you