This is pretty good (from U.S. Tsubaki). It's only on-line (no PDF), but you might be able to request a copy from them:
http://chain-guide.com/toc.html
There is some gear engineering reference info near the back of this Boston Gear catalog:
http://www.bostongear.com/litportal/...%20PAGESsm.pdf
If you want reference material on gearing, power transmission or general mechanics and machining, try searching on one of those terms in Google Books. The trick is to then do an advanced search and select FULL VIEW. That will get you all the old books that are out of copyright, and you can download them. I've found dozens of great books. Not a whole lot has happened to gearing over the last 80 years or so that would apply to our robots, except we've all but forgotten how to make the big ones and the machinery to do it. If you don't believe me, go to this link, and scroll through ALL the pictures - the gears are toward the bottom.
http://www.practicalmachinist.com/vb...d.php?t=148241
Hare's a book that might be useful:
http://books.google.com/books?id=T-k...sms&as_br r=1