Just seating at the computer and  thought..    WHAT CONTROLS THE SPEED (RPM) of motor ? the ESC or timer?

Just seating at the computer and  thought..    WHAT CONTROLS THE SPEED (RPM) of motor ? the ESC or timer?

Both - plus the prop and the battery

On a control line stunt setup, you set the speed with the timer.
though in some cases with the castle creations speed controler, you can set rpm response settings, so if the timer asks for a setting between 0% and (?) % it will  run the engine at the preset rpm. I dont use this setting so I am only aware it exists and basically how it works, I think Alan Hahn uses it more, perhaps he will chime in
Ultimatly the timer still sets the called for rpm speed. The timer acts like the radio reciever

As Mark says, it depends!!

With the CC Phoenix ESC, there are 2 basic governor modes, the newer one which is "Set RPM mode" and the other which is called "Simple Governor mode".

The Set RPM mode has 3 set target rpm values, one for the timer throttle settings less than 50%, a second for throttle greater than 50% but less than 99%,  and a third for 100% throttle. So you could set 7000, 8000, 9000 rpm targets, and depending on how you set the timer throttle output, you would get one of those 3 rpms--and nothing in between--except for zero rpm for zero throttle of course!

The Simple governor mode is a bit different. It sets a limited range of rpm values that corresponds to the throttle settings. In addition there is a "high" and "low" setting which sets two different ranges. I use to use this, but I've forgotten exactly how to do it right now.

I use the set rpm mode, it has its pluses and minuses. The plus is that if you know what rpm you want, it is easy. The minus is that you need to know the rpm--there is no adjustment you can do at the field to tweak the values you choose--without having a computer. You could of course use the 3 settings to bracket a range and use the timer to choose one of the 3, in order to zero in on the final value that you want.