How do make a 9-18vdc motor more powerful??

Question

I have a 9-18vdc motor from radio shack.My project is to hook a toy wheel onto that shaft. Make the wheel hit a bunch of loose playing cards into the air 7-8 feet high. I have already built a unit that can do it using the same motor and a Duracell 9v battery,but the cards only goes 3ft into the air. Maybe it is the wheel that doesn't have enough grip. i'll try to replace the wheel but what i want to know is

How can i increase the speed of the motor. i don't really know much on the subject so i'm guessing if i got more voltage into the motor then wheel will spin at a higher rate. So how can i increase 9v to 18v? is there a battery that is 18v? Or maybe a new motor?

Answer 1

2- 9v batteries in series = 18v.

Series= from motor to bat 1 neg, bat 1pos to bat 2 neg, bat 2 pos to motor