Can I remove the optical drive in a Lenovo y50 and put in another hard drive?

I don't know that your model of lenovo has a ultra bay for additional gpu or hdd, the answer is no for putting a hdd in the optical drive slot

I have never done this but know someone that has.
There's a caddy available for this for most 2.5" hard drive and SSD. It is only available from Germany as far as I'm aware.
Look at the following Web page.
There are several different sizes so you will have to measure.

http://www.newmodeus.de/en/index.html

Hope this gives you what you want