Summary

UPDATE: Check out the new improved version here: http://www.thingiverse.com/thing:1421337 - it includes an option for free spinning wheels that attach to any Cubelet.

These are magnetically attachable wheels for the Cubelets system from Modular Robotics, a construction system for quickly building robots. They are designed to attach to the "Rotate" Cubelet to give robots greater mobility. You will need to reprogram the Cubelets in opposing sides to turn counter-clockwise.

It requires washers, and o-rings to use as the tires. The washers I used have an outer diameter of 1" and an inner diameter of 1/2". The dimensions are in the OpenSCAD file, so you can change them. You can probably get by with an OD 1mm smaller and/or an ID up 5mm larger. A larger ID will give a stronger piece, since it will allow the "pie slices" to overlap the hub more. Check McMaster Carr and see what they have...

The o-rings I used for the medium wheel have an OD of 2 7/8" and an ID of 2 1/2". You can change this in the OpenSCAD file too. RC car tires would probably look cool.

For assembly, print the wheel of your choice and the connector housing. You should use support material when printing the wheel in order to fill in the well for the connector. Fit the washer into the connector housing. Then press the connector housing into the wheel hub. Use glue if you want, but the friction fit is pretty good.

The OpenSCAD file contains a bunch of utilities that can be used to make other Cubelets accessories. I am planning on making a pen holder, for example.

IMPORTANT NOTE REGARDING MAGNETS: The pictures show a version of the connector with 1/8" magnets fitted. These provide a better connection, but are not recommended if you will use the wheels with small children, since the magnets could get loose and be swallowed. So I have uploaded the connector WITHOUT magnets, since this works fine and is safer. If you really want the magnets, you should be able to figure out how to get that version of the connector.

ANOTHER NOTE ABOUT MAGNETS: Should you use the magnets, be aware that there is a correct polarity for installing them. They should be oriented such that they repel the magnets on a regular Cubelet. That way, when you bring them together, the magnets will repel each other, and instead seek out the washer, aligning the connector correctly. If the magnets are installed such that they attract the magnets on the Cubelet, then they will tend to stick magnet-to-magnet, and will require a twist and push to get them into the right orientation.