It varies from prop to prop.
Its usually either a 6vdc 8vdc or 12vdc motor.
Sad part is most of the time it's not the motor that goes bad, its the control board in the bottom.
Those things have extremely weak power supplies on the board that fail all the time.
For example if a motor goes one direction but wont reverse on its own only if you gently force it then you have a bad power supply on the board.
I have been plagued over the past few months with people ( some on this forum that have sent me they're Gemmy life size animated props only to find out there's nothing I could do to fix them.
Gears can be replaced if stripped, motors can be replaced if burnt or acting jittery ( usually the caps or resistors in line ) but if the motor isn't getting equal voltage in forward and then reverse you have a bad board but even then......it can get even trickier.
I'm actually in the process of fixing a arm on a Michael Myers Rob Zombie newer version right now and I replaced the capacitors on the motor, installed a new motor and inline resistor and even though the voltage was there there wasn't enough current / amps to drive the motor in reverse and the only real way to know if the current is right is to have a 100 percent guaranteed working motor with 100 percent guaranteed working capacitors to know the true load.
Only to find out that all the work was in vain.
I'm a electronics engineer and a mechanical engineer and after having a bunch of these guys apart for repair, I even tried to tackle how to fix the control boards and let me just say for the record ( Jesus on crutches ) that the design of the board and lay out is insaine, they use the tightest packed board with the absolute cheapest parts they can grab and throw together and don't even get me started on the soldering jobs.
I've seen 15yr old hobbies do a better job at soldering, cold soldiers all over the place, so bad that you might get lucky and find a intermittent problem was due to a crappy cold solder.