Thanks both. The motor will be a non-sensored brushless outrunner something along these lines:
http://www.rapidrcmodels.com/turnigy-d35365-1450kv-brushless-outrunner-motor-306-p.asp

Sensored would be the way to go, but the motors and ESCs are both more pricey. They usually have a trio of sensors set around the armature at 120 degrees to provide RPM feedback to the ESC.

 

Thanks both. The motor will be a non-sensored brushless outrunner something along these lines:
http://www.rapidrcmodels.com/turnigy-d35365-1450kv-brushless-outrunner-motor-306-p.asp

Sensored would be the way to go, but the motors and ESCs are both more pricey. They usually have a trio of sensors set around the armature at 120 degrees to provide RPM feedback to the ESC.

Well, if the motor already has sensors, then you might as well make a "Y" splice on one of them and feed it to the missing pulse detector circuit whose diagram I already posted, substituting the hall sensor. Assuming that the sensor's signal level is digital (completely on and completely off) and it's 5V, of course. If it's not 5V then you'd have to make a small signal translator circuit, and if it's not digital (could be sinusoidal) then you'd have to feed its output to a comparator so as to "digitalize" the signal.