What is typically used to start a synchronous motor? rotor construction.

 

There are a few types, so it depends if you are looking to zero in on a particular type?
Before the days of quartz crystal for time keeping, a shaded pole motor was used in miniature applications such as wall clocks, these used a pair of shaded pole or shorted copper turns to create an out of phase magnetic field in the rotor.
As opposed to a normal induction motor that cannot be ran at synchronism, unless like some very large motors (50hp and up) that had a winding on the rotor that was brought out via two slip rings were ran up initially as an induction motor, the slip frequency was detected via the slip rings, and when the slip was within around 5 Hz, a DC voltage was injected into the slip ring rotor, and the motor came up to synchronism.
There is also the Permanent magnet rotor type with AC 3 ph stator.
Max.

 

Hello,

The following page of the EDUCYPEDIA has some link with information for you:
http://educypedia.karadimov.info/electronics/Synchronousmotor.htm

Bertus

 

I just noticed this question is in the "homework help" section, so I hesitate to give you a straight answer. However, I suggest you look up the phrase "squirrel cage" in the context of synchronous motors. You might learn something