Woah now, flag this thred for misinformation...
You all have it quite wrong except for Wendigo.
Rotation was changed quite a while ago to be controlled properly by the rail speed controler. In the current build there is some wonky-ness that causes the rail to lock up if you don't do it in this exact manner:
1: place your rotar and dock your ship core to it.
2: place a button directly behind the rotor, activate it and get that puppy spinning.
3: place a rail speed controler and link it to the rail rotor. Select the controler with "C" and click on the rail rotor with "V"
4: place 8 or so activation blocks and link then to the controler. Selecting the speed controler with "C" and clicking on each of the individual activation block with "V"
At this point, with all the activation block off, the rotor will be stopped. As you turn them on one by one the rotor will speed up. Turn on blocks, or add more blocks until you reach your desired speed. The more activation blocks you have the more you can control the speed of the rotor.
So now that first button you placed no longer controls the rotor. All it does it send out a pulse each time the rotor turns. You can now use that button to make clocks and stuff.
Hope that helps