The above view is the complete LEGO CAD model of The Inch Worm
using LEGO Educational Motorized Simple Machine set.
See examples below on how to construct the inch worm using the Cities and Transportation LEGO set.

This is what needs to be built as a base model for the inch worm.  There are variations on style for constructing the arm and placement of the motor.
 

The most important part of the Inch Worm is the pawl and ratchet on each axle.

At this point the motor block Green G instructions are added.
The only difference is that a crown gear is used instead of the 24 tooth spur so that two could be used for ratchets.
Place a 40 tooth gear on the 4 axle. Add a gray connector in an outside hole.

The pawl and ratchet are to be set so that both the front and the back wheels roll only forward.
The middle folds up and the 16 beam connects to the connector in the 40 tooth gear.
As the motor rotates the 40 tooth gear the 16 beam  moves back and forth (actually it is reciprocating motion).
Take care that the axle through the crown gear in the gear box does not come out
of the 40 tooth gear as it would then bind against the beam and stall the motor.
 

See pictures of lots of inch worm.

This page was started to give LEGO Robotics Camp Summer 2005 ideas for building critters.

Inchworm on July 22, 2009

Below are some ideas for the Cities and Transportation sets.

The arm in this picture is constructed with a sixteen beam.
The motor block is similar to the one above however the motor is geared down internally.
There is no 40 tooth gear so the small half beams are used.

 Instead of using such a slow gear train, an 8 tooth gear meshing with a 40 tooth is three times faster.
 An eight beam is used for the rotating part of the arm  while the reciprocating beam is a twelve.
The arms are held in place with connectors and bushings, wheels are added to both sides.

Print version