To attach the flippers to the motors, we will use a snap on motor hub. 

Zip ties or twist ties work great as a method of attachment.

Mark the position of the motor hub against your flipper.

Poke two holes through flipper using something pointy. 

Use zip-ties or twist-ties to hold flipper to motor hub.

Repeat the process for the second flipper.

Depending on your design, you may need to trim the edges of the flipper so that's it's not quite as long.

This step is important to allow the motors to spin all the way around and not get stuck. 

Once these flippers are to your satisfaction, it's time to get them moving!

Let's add some electronics...