Instructables

Step 9:

Follow the images for this step because it sounds tricky even though it is easy.

15. With the jar sitting on its base like normal, and the motor/lid assembly attached, lay a rubber band over top of the motor.  Using 1 hand hold both sides of the rubber band down, this will put a little downward pressure on the motor.  Now take a second rubber band and fasten it over the first.  - See image.  
Then, take the 2 sides of the first rubber band, which you should still be holding and curl them up and around the 2nd rubber band, then put the toothpick/skewer through the 2 available loops.  -See images if this description is lacking.

16. With the skewer holding the rubber band in place, add a dab of hot glue to the ends of the skewer, over the rubber band to hold it in place.  Then snip off the excess wood.