Craft tube bearings for Smartrap

Walk into most any Ace Hardware or hobby store and you'll find an [assortment of hollow tubes in different sizes and metals](http://shop.hobbylobby.com/products/7/32-brass-tube-101378/)

I've chosen to update my Smartrap to use these craft tubes as smooth rods. I find they have a number of advantages over the conventional solid smooth rods. They are:

* smoother than conventional rods offered by hardware stores
* cheaper than rods made specially for linear motion
* readily availabl