Turned my disk freehub into a fixed gear by replacing my brake rotor with a cog. I precisely centering a cog under the rotor, secured it with two visegrips, and drilled out the rotor bolt holes. I used cutting oil, high quality drill bit, and a variable speed drill.
I can now experience direct drive. (Zac enlightened me about my mistake. Direct drive has no gears and applies to a unicycle, high wheel, and kid's tricycle. Mine is a fix, fixy, or fixed drivetrain.)
On the snow covered neighborhood streets, I eagerly took my first fixed ride. It was different. Started with pedal at 2:00, pushed down and then got lifted up off the seat from the upstroke before I got my other foot clipped in. Unclip one foot to stop and the other keeps turning. Trying to brake with back pressure going downhill felt really weird. Definitely using the leg muscles in a different way.
It is like learning to ride again. As long as I'm maintaining or increasing cadence while seated or standing in a straight line, the fixed felt familiar. Starting, slowing, stopping, and corners felt strange. Imagine how singletrack and ttfs will feel! The endos and crashes will feel the same, successful negotiation of ttfs will be something else. New skills will be needed.