New Rotocaster Omni-Directional Wheel

While these are often used on robots with three wheels where all three rotate at different rates allowing the robot to go in any direction,

Three-Wheeled Omni-Wheel Prototype by Xander Soldaat at Bot Bench (click on image to see more)

There are several different options that one can consider. LEGO purists may consider making their own omni-directional wheel designs out of only official LEGO parts. Another option is to purchase manufactured omni-directional wheels. These come in two classes: those that are designed to be LEGO compatible, and those that are not LEGO compatible. In the latter case, one would have to construct some kind of coupling mechanism to enable the wheel to connect to LEGO parts.

Here are some of the options that I have found.

Omni-Directional Wheels Constructed from LEGO Parts

Omni-Directional LEGO Wheels by Xander at Bot Bench
These wheels use the LEGO pulley to get a six-fold symmetry. Each “wheel” uses 12 LEGO wheels. For archiving purposes, here are three pictures. Please visit Xander at Bot Bench for larger images and more details.

Omni-Directional LEGO Wheels by Xander Soldaat at Bot Bench

Details of Omni-Directional LEGO Wheels by Xander Soldaat at Bot Bench

Details of Omni-Directional LEGO Wheels by Xander Soldaat at Bot Bench

This amazing tank by Peer Kreuger also sports omni-directional wheels made from LEGO parts

LEGO Tank with LEGO Omni-Directional Wheels

The Omni Bot v2 by jason701802 also sports omni-directional wheels

Omni Bot v2 by jason701802

LEGO-compatible Manufactured Omni-Directional Wheels

This LEGO-compatible wheel is made by the School of Robotics

School of Robotics Omni-Directional Wheels

Rotacaster makes a LEGO-compatible omni-directional wheel:

Rotacaster Robot Wheel (LEGO-compatible)

Rotacaster is also coming out with a new design

New Rotocaster Omni-Directional Wheel

Rotacaster also produces several non-LEGO compatible designs.

Tetrix also makes LEGO-compatible Omni-Directional Wheels

Tetrix Omni-Directional Wheels

General Manufactured Omni-Directional Wheels

Mecanum Omni-Wheel Designed by Bengt Ilon in 1973 at the Mecanum AB Company

Mecanum Wheel

Mecanum Omni-Directional Wheel

Vex Omni-Directional Wheel

Vex Omni-Directional Wheel

Damon WH-01 Omni Directional Wheel (hexagon hole)
(Outer Diameter:60mm, Inner Diameter:11mm, Material: Nylon)

Damon WH-01 Omni-Directional Wheel

Kornylak Omni-Directional Wheel

Kornylak Omni-Directional Wheel

Kornylak Transwheel

Kornylak Transwheel

Kornylak Omni-Directional Wheel

Kornylak Omni-Directional Wheel

There are several ways to find the Center of Mass of the motor.  The most straightforward way is to hang the motor from an axle placed in one of the holes.  The motor will orient itself so that the Center of Mass lies directly below the axle.  By hanging a mass on a string from the axle, the Center of Mass must lie somewhere along the line defined by the string. 

After performing this experiment, I placed a small piece of Scotch tape over the string so that I can keep track of where that line is.  I then cut the string off of the axle.

Now to find the precise point, we simply perform the experiment again, but place the axle through a different hole.  This gives us a second line.  Since the Center of Mass must be on both the first line and the second line, it is located at the intersection of these two lines.

The Center of Mass is very close to being aligned with the holes on the motor.  Below is an MLCAD image of the NXT motor (from Philo).  I have overlayed a Cartesian coordinate system that corresponds to that used to define the 3-D image file.  The origin of this system is at the center of the axle hole on the motors drive axis.  This is perfect for me since I will be rotating the motor and trying to compute the position of the Center of Mass after the motor has rotated through some arbitrary angle.

This image not only helps with identifying the Center of Mass of the NXT motor, but also in understanding the dimensions of the NXT motor overall.

Kevin Knuth
Albany NY