You're probably thinking "a worm gear...big deal". Well actually you're right, it is a big deal. It offers a means of providing well defined and finite motion in Lego builds all wrapped up in a very small package. Better yet, if you have access to a decent 3D printer the cost of printing all you could ever need is truly negligible.
Step 1: The Serendipity Moment
The serendipity moment came with the realization the commonly available miniature N20 gear motors fit easily but snugly into the side of the Lego worm gear blocks and stay put with no additional mounting hardware. This made for a very simple plug and play method of creating motion with the Lego gears. Problem was that the D shaped shaft of the motor would not interface with the cross shaped opening of the worm gear. Sure you could drill out the Lego worm gear and glue the motor into place but that kind of defeats the plug and play potential the system offers. So time to put modern 3D printing to use and create a worm gear with a D-shaped input.
Step 2: Uses
The model shown above which includes a 100 RPM motor, a low voltage PWM generator and a 9V power supply probably represents the worst possible use of this concept as all it created was the world's slowest dune buggy but sadly that's about the extent of my remaining Lego collection. The intended use however was propelling a time lapse camera slider but as of this writing is still awaiting parts coming snail mail.
The reality is however that with motors available anywhere from 10 to 300 rpm this concept offers opportunities in a vast array of projects anywhere from robot armatures to steam shovel models as the motors are easily reversible and the main gear stays put where the worm gear stops. And with the N20 gear motors generally available in the $3-$5 range and coming in a wide variety of speeds combined with easy swapability, this concept offers a wide range of potential very inexpensively.
If you've already got a use in mind, please leave a comment and let us know what you envision.
Thank you for giving my instructable a moment of your time.