Give me a day, there's got to be an ultra simple way to do this without any low voltage supply, 555, and optocoupler.
In the mean time, this is not my circuit, I just googled it: (It appears to depend on the current consumption of the motor's main winding, IE, if the motor is turning too slow, the triac gate is turned on and powers the starter coil. This also means when running, if you physically stop/break the motor speed too slow, the start coil will once again be energized until the motor is spinning fast enough. Also, I assume the caps in the circuit are AC, not DC as drawn! I also suspect you would want to add a series resistor, something like 100ohm, on the gate of the triac.)